MLECO-3077: Add ASR use case API

* Minor adjustments to doc strings in KWS
* Remove unused score threshold in KWS

Signed-off-by: Richard Burton <richard.burton@arm.com>
Change-Id: Ie1c5bf6f7bdbebb853b6a10cb7ba1c4a1d9a76c9

17 files changed, 495 insertions, 594 deletions

diff --git a/source/use_case/asr/include/AsrResult.hpp b/source/use_case/asr/include/AsrResult.hpp
index b12ed7d..ed826d0 100644
--- a/source/use_case/asr/include/AsrResult.hpp
+++ b/source/use_case/asr/include/AsrResult.hpp
@@ -25,7 +25,7 @@ namespace arm {
 namespace app {
 namespace asr {
 
-    using ResultVec = std::vector < arm::app::ClassificationResult >;
+    using ResultVec = std::vector<arm::app::ClassificationResult>;
 
     /* Structure for holding ASR result. */
     class AsrResult {
diff --git a/source/use_case/asr/include/Wav2LetterModel.hpp b/source/use_case/asr/include/Wav2LetterModel.hpp
index 55395b9..895df2b 100644
--- a/source/use_case/asr/include/Wav2LetterModel.hpp
+++ b/source/use_case/asr/include/Wav2LetterModel.hpp
@@ -36,6 +36,9 @@ namespace app {
         static constexpr uint32_t ms_outputRowsIdx = 2;
         static constexpr uint32_t ms_outputColsIdx = 3;
 
+        static constexpr uint32_t ms_blankTokenIdx   = 28;
+        static constexpr uint32_t ms_numMfccFeatures = 13;
+
     protected:
         /** @brief   Gets the reference to op resolver interface class. */
         const tflite::MicroOpResolver& GetOpResolver() override;
diff --git a/source/use_case/asr/include/Wav2LetterPostprocess.hpp b/source/use_case/asr/include/Wav2LetterPostprocess.hpp
index 29eb548..45defa5 100644
--- a/source/use_case/asr/include/Wav2LetterPostprocess.hpp
+++ b/source/use_case/asr/include/Wav2LetterPostprocess.hpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021 Arm Limited. All rights reserved.
+ * Copyright (c) 2021-2022 Arm Limited. All rights reserved.
  * SPDX-License-Identifier: Apache-2.0
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
@@ -17,93 +17,90 @@
 #ifndef ASR_WAV2LETTER_POSTPROCESS_HPP
 #define ASR_WAV2LETTER_POSTPROCESS_HPP
 
-#include "TensorFlowLiteMicro.hpp" /* TensorFlow headers. */
+#include "TensorFlowLiteMicro.hpp"   /* TensorFlow headers. */
+#include "BaseProcessing.hpp"
+#include "AsrClassifier.hpp"
+#include "AsrResult.hpp"
 #include "log_macros.h"
 
 namespace arm {
 namespace app {
-namespace audio {
-namespace asr {
 
     /**
      * @brief   Helper class to manage tensor post-processing for "wav2letter"
      *          output.
      */
-    class Postprocess {
+    class ASRPostProcess : public BasePostProcess {
     public:
+        bool m_lastIteration = false;   /* Flag to set if processing the last set of data for a clip. */
+
         /**
-         * @brief       Constructor
-         * @param[in]   contextLen      Left and right context length for
-         *                              output tensor.
-         * @param[in]   innerLen        This is the length of the section
-         *                              between left and right context.
-         * @param[in]   blankTokenIdx  Blank token index.
+         * @brief           Constructor
+         * @param[in]       outputTensor       Pointer to the output Tensor.
+         * @param[in]       labels             Vector of string labels to identify each output of the model.
+         * @param[in/out]   result            Vector of classification results to store decoded outputs.
+         * @param[in]       outputContextLen   Left/right context length for output tensor.
+         * @param[in]       blankTokenIdx      Index in the labels that the "Blank token" takes.
+         * @param[in]       reductionAxis      The axis that the logits of each time step is on.
          **/
-        Postprocess(uint32_t contextLen,
-                    uint32_t innerLen,
-                    uint32_t blankTokenIdx);
-
-        Postprocess() = delete;
-        ~Postprocess() = default;
+        ASRPostProcess(AsrClassifier& classifier, TfLiteTensor* outputTensor,
+                const std::vector<std::string>& labels, asr::ResultVec& result,
+                uint32_t outputContextLen,
+                uint32_t blankTokenIdx, uint32_t reductionAxis);
 
         /**
-         * @brief       Erases the required part of the tensor based
-         *              on context lengths set up during initialisation.
-         * @param[in]   tensor          Pointer to the tensor.
-         * @param[in]   axisIdx         Index of the axis on which erase is
-         *                              performed.
-         * @param[in]   lastIteration   Flag to signal this is the
-         *                              last iteration in which case
-         *                              the right context is preserved.
-         * @return      true if successful, false otherwise.
-         */
-        bool Invoke(TfLiteTensor*  tensor,
-                    uint32_t axisIdx,
-                    bool lastIteration = false);
+         * @brief    Should perform post-processing of the result of inference then
+         *           populate ASR result data for any later use.
+         * @return   true if successful, false otherwise.
+         **/
+        bool DoPostProcess() override;
+
+        /** @brief   Gets the output inner length for post-processing. */
+        static uint32_t GetOutputInnerLen(const TfLiteTensor*, uint32_t outputCtxLen);
+
+        /** @brief   Gets the output context length (left/right) for post-processing. */
+        static uint32_t GetOutputContextLen(const Model& model, uint32_t inputCtxLen);
+
+        /** @brief   Gets the number of feature vectors to be computed. */
+        static uint32_t GetNumFeatureVectors(const Model& model);
 
     private:
-        uint32_t    m_contextLen;      /* lengths of left and right contexts. */
-        uint32_t    m_innerLen;        /* Length of inner context. */
-        uint32_t    m_totalLen;        /* Total length of the required axis. */
-        uint32_t    m_countIterations; /* Current number of iterations. */
-        uint32_t    m_blankTokenIdx;   /* Index of the labels blank token. */
+        AsrClassifier& m_classifier;                /* ASR Classifier object. */
+        TfLiteTensor* m_outputTensor;               /* Model output tensor. */
+        const std::vector<std::string>& m_labels;   /* ASR Labels. */
+        asr::ResultVec & m_results;                 /* Results vector for a single inference. */
+        uint32_t m_outputContextLen;                /* lengths of left/right contexts for output. */
+        uint32_t m_outputInnerLen;                  /* Length of output inner context. */
+        uint32_t m_totalLen;                        /* Total length of the required axis. */
+        uint32_t m_countIterations;                 /* Current number of iterations. */
+        uint32_t m_blankTokenIdx;                   /* Index of the labels blank token. */
+        uint32_t m_reductionAxisIdx;                /* Axis containing output logits for a single step. */
+
         /**
-         * @brief       Checks if the tensor and axis index are valid
-         *              inputs to the object - based on how it has been
-         *              initialised.
-         * @return      true if valid, false otherwise.
+         * @brief    Checks if the tensor and axis index are valid
+         *           inputs to the object - based on how it has been initialised.
+         * @return   true if valid, false otherwise.
          */
         bool IsInputValid(TfLiteTensor*  tensor,
-                          const uint32_t axisIdx) const;
+                          uint32_t axisIdx) const;
 
         /**
-         * @brief       Gets the tensor data element size in bytes based
-         *              on the tensor type.
-         * @return      Size in bytes, 0 if not supported.
+         * @brief    Gets the tensor data element size in bytes based
+         *           on the tensor type.
+         * @return   Size in bytes, 0 if not supported.
          */
         static uint32_t GetTensorElementSize(TfLiteTensor* tensor);
 
         /**
-         * @brief       Erases sections from the data assuming row-wise
-         *              arrangement along the context axis.
-         * @return      true if successful, false otherwise.
+         * @brief    Erases sections from the data assuming row-wise
+         *           arrangement along the context axis.
+         * @return   true if successful, false otherwise.
          */
         bool EraseSectionsRowWise(uint8_t* ptrData,
-                                  const uint32_t strideSzBytes,
-                                  const bool lastIteration);
-
-        /**
-         * @brief       Erases sections from the data assuming col-wise
-         *              arrangement along the context axis.
-         * @return      true if successful, false otherwise.
-         */
-        static bool EraseSectionsColWise(const uint8_t* ptrData,
-                                  const uint32_t strideSzBytes,
-                                  const bool lastIteration);
+                                  uint32_t strideSzBytes,
+                                  bool lastIteration);
     };
 
-} /* namespace asr */
-} /* namespace audio */
 } /* namespace app */
 } /* namespace arm */
 
diff --git a/source/use_case/asr/include/Wav2LetterPreprocess.hpp b/source/use_case/asr/include/Wav2LetterPreprocess.hpp
index 13d1589..8c12b3d 100644
--- a/source/use_case/asr/include/Wav2LetterPreprocess.hpp
+++ b/source/use_case/asr/include/Wav2LetterPreprocess.hpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021 Arm Limited. All rights reserved.
+ * Copyright (c) 2021-2022 Arm Limited. All rights reserved.
  * SPDX-License-Identifier: Apache-2.0
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
@@ -21,49 +21,44 @@
 #include "Wav2LetterMfcc.hpp"
 #include "AudioUtils.hpp"
 #include "DataStructures.hpp"
+#include "BaseProcessing.hpp"
 #include "log_macros.h"
 
 namespace arm {
 namespace app {
-namespace audio {
-namespace asr {
 
     /* Class to facilitate pre-processing calculation for Wav2Letter model
      * for ASR. */
-    using AudioWindow = SlidingWindow <const int16_t>;
+    using AudioWindow = audio::SlidingWindow<const int16_t>;
 
-    class Preprocess {
+    class ASRPreProcess : public BasePreProcess {
     public:
         /**
          * @brief       Constructor.
-         * @param[in]   numMfccFeatures   Number of MFCC features per window.
-         * @param[in]   windowLen         Number of elements in a window.
-         * @param[in]   windowStride      Stride (in number of elements) for
-         *                                moving the window.
-         * @param[in]   numMfccVectors    Number of MFCC vectors per window.
+         * @param[in]   inputTensor        Pointer to the TFLite Micro input Tensor.
+         * @param[in]   numMfccFeatures    Number of MFCC features per window.
+         * @param[in]   mfccWindowLen      Number of audio elements to calculate MFCC features per window.
+         * @param[in]   mfccWindowStride   Stride (in number of elements) for moving the MFCC window.
+         * @param[in]   mfccWindowStride   Number of MFCC vectors that need to be calculated
+         *                                 for an inference.
          */
-        Preprocess(
-            uint32_t  numMfccFeatures,
-            uint32_t  windowLen,
-            uint32_t  windowStride,
-            uint32_t  numMfccVectors);
-        Preprocess() = delete;
-        ~Preprocess() = default;
+        ASRPreProcess(TfLiteTensor* inputTensor,
+                uint32_t  numMfccFeatures,
+                uint32_t  audioWindowLen,
+                uint32_t  mfccWindowLen,
+                uint32_t  mfccWindowStride);
 
         /**
          * @brief       Calculates the features required from audio data. This
          *              includes MFCC, first and second order deltas,
          *              normalisation and finally, quantisation. The tensor is
-         *              populated with feature from a given window placed along
+         *              populated with features from a given window placed along
          *              in a single row.
          * @param[in]   audioData      Pointer to the first element of audio data.
          * @param[in]   audioDataLen   Number of elements in the audio data.
-         * @param[in]   tensor         Tensor to be populated.
          * @return      true if successful, false in case of error.
          */
-        bool Invoke(const int16_t * audioData,
-                    uint32_t  audioDataLen,
-                    TfLiteTensor *  tensor);
+        bool DoPreProcess(const void* audioData, size_t audioDataLen) override;
 
     protected:
          /**
@@ -80,32 +75,16 @@ namespace asr {
                                    Array2d<float>& delta2);
 
         /**
-         * @brief       Given a 2D vector of floats, computes the mean.
-         * @param[in]   vec   Vctor of vector of floats.
-         * @return      Mean value.
-         */
-        static float GetMean(Array2d<float>& vec);
-
-        /**
-         * @brief       Given a 2D vector of floats, computes the stddev.
-         * @param[in]   vec    Vector of vector of floats.
-         * @param[in]   mean   Mean value of the vector passed in.
-         * @return      stddev value.
-         */
-        static float GetStdDev(Array2d<float>& vec,
-                               const float mean);
-
-        /**
-         * @brief           Given a 2D vector of floats, normalises it using
-         *                  the mean and the stddev.
+         * @brief           Given a 2D vector of floats, rescale it to have mean of 0 and
+        *                   standard deviation of 1.
          * @param[in,out]   vec   Vector of vector of floats.
          */
-        static void NormaliseVec(Array2d<float>& vec);
+        static void StandardizeVecF32(Array2d<float>& vec);
 
         /**
-         * @brief   Normalises the MFCC and delta buffers.
+         * @brief   Standardizes all the MFCC and delta buffers to have mean 0 and std. dev 1.
          */
-        void Normalise();
+        void Standarize();
 
         /**
          * @brief       Given the quantisation and data type limits, computes
@@ -139,7 +118,7 @@ namespace asr {
          */
         template <typename T>
         bool Quantise(
-                T *             outputBuf,
+                T*              outputBuf,
                 const uint32_t  outputBufSz,
                 const float     quantScale,
                 const int       quantOffset)
@@ -160,15 +139,15 @@ namespace asr {
             const float maxVal = std::numeric_limits<T>::max();
 
             /* Need to transpose while copying and concatenating the tensor. */
-            for (uint32_t j = 0; j < this->m_numFeatVectors; ++j) {
+            for (uint32_t j = 0; j < this->m_numFeatureFrames; ++j) {
                 for (uint32_t i = 0; i < this->m_numMfccFeats; ++i) {
-                    *outputBufMfcc++ = static_cast<T>(Preprocess::GetQuantElem(
+                    *outputBufMfcc++ = static_cast<T>(ASRPreProcess::GetQuantElem(
                             this->m_mfccBuf(i, j), quantScale,
                             quantOffset, minVal, maxVal));
-                    *outputBufD1++ = static_cast<T>(Preprocess::GetQuantElem(
+                    *outputBufD1++ = static_cast<T>(ASRPreProcess::GetQuantElem(
                             this->m_delta1Buf(i, j), quantScale,
                             quantOffset, minVal, maxVal));
-                    *outputBufD2++ = static_cast<T>(Preprocess::GetQuantElem(
+                    *outputBufD2++ = static_cast<T>(ASRPreProcess::GetQuantElem(
                             this->m_delta2Buf(i, j), quantScale,
                             quantOffset, minVal, maxVal));
                 }
@@ -181,23 +160,22 @@ namespace asr {
         }
 
     private:
-        Wav2LetterMFCC      m_mfcc;            /* MFCC instance. */
+        audio::Wav2LetterMFCC   m_mfcc;          /* MFCC instance. */
+        TfLiteTensor*           m_inputTensor;   /* Model input tensor. */
 
         /* Actual buffers to be populated. */
-        Array2d<float>      m_mfccBuf;         /* Contiguous buffer 1D: MFCC */
-        Array2d<float>      m_delta1Buf;       /* Contiguous buffer 1D: Delta 1 */
-        Array2d<float>      m_delta2Buf;       /* Contiguous buffer 1D: Delta 2 */
+        Array2d<float>   m_mfccBuf;              /* Contiguous buffer 1D: MFCC */
+        Array2d<float>   m_delta1Buf;            /* Contiguous buffer 1D: Delta 1 */
+        Array2d<float>   m_delta2Buf;            /* Contiguous buffer 1D: Delta 2 */
 
-        uint32_t            m_windowLen;       /* Window length for MFCC. */
-        uint32_t            m_windowStride;    /* Window stride len for MFCC. */
-        uint32_t            m_numMfccFeats;    /* Number of MFCC features per window. */
-        uint32_t            m_numFeatVectors;  /* Number of m_numMfccFeats. */
-        AudioWindow         m_window;          /* Sliding window. */
+        uint32_t         m_mfccWindowLen;        /* Window length for MFCC. */
+        uint32_t         m_mfccWindowStride;     /* Window stride len for MFCC. */
+        uint32_t         m_numMfccFeats;         /* Number of MFCC features per window. */
+        uint32_t         m_numFeatureFrames;     /* How many sets of m_numMfccFeats. */
+        AudioWindow      m_mfccSlidingWindow;    /* Sliding window to calculate MFCCs. */
 
     };
 
-} /* namespace asr */
-} /* namespace audio */
 } /* namespace app */
 } /* namespace arm */
 
diff --git a/source/use_case/asr/src/MainLoop.cc b/source/use_case/asr/src/MainLoop.cc
index 51b0b18..a1a9540 100644
--- a/source/use_case/asr/src/MainLoop.cc
+++ b/source/use_case/asr/src/MainLoop.cc
@@ -14,15 +14,12 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-#include "hal.h"                     /* Brings in platform definitions. */
 #include "Labels.hpp"                /* For label strings. */
 #include "UseCaseHandler.hpp"        /* Handlers for different user options. */
 #include "Wav2LetterModel.hpp"       /* Model class for running inference. */
 #include "UseCaseCommonUtils.hpp"    /* Utils functions. */
 #include "AsrClassifier.hpp"         /* Classifier. */
 #include "InputFiles.hpp"            /* Generated audio clip header. */
-#include "Wav2LetterPreprocess.hpp"  /* Pre-processing class. */
-#include "Wav2LetterPostprocess.hpp" /* Post-processing class. */
 #include "log_macros.h"
 
 enum opcodes
@@ -48,23 +45,9 @@ static void DisplayMenu()
     fflush(stdout);
 }
 
-/** @brief Verify input and output tensor are of certain min dimensions. */
+/** @brief   Verify input and output tensor are of certain min dimensions. */
 static bool VerifyTensorDimensions(const arm::app::Model& model);
 
-/** @brief Gets the number of MFCC features for a single window. */
-static uint32_t GetNumMfccFeatures(const arm::app::Model& model);
-
-/** @brief Gets the number of MFCC feature vectors to be computed. */
-static uint32_t GetNumMfccFeatureVectors(const arm::app::Model& model);
-
-/** @brief Gets the output context length (left and right) for post-processing. */
-static uint32_t GetOutputContextLen(const arm::app::Model& model,
-                                    uint32_t inputCtxLen);
-
-/** @brief Gets the output inner length for post-processing. */
-static uint32_t GetOutputInnerLen(const arm::app::Model& model,
-                                  uint32_t outputCtxLen);
-
 void main_loop()
 {
     arm::app::Wav2LetterModel model;  /* Model wrapper object. */
@@ -78,21 +61,6 @@ void main_loop()
         return;
     }
 
-    /* Initialise pre-processing. */
-    arm::app::audio::asr::Preprocess prep(
-                                GetNumMfccFeatures(model),
-                                g_FrameLength,
-                                g_FrameStride,
-                                GetNumMfccFeatureVectors(model));
-
-    /* Initialise post-processing. */
-    const uint32_t outputCtxLen = GetOutputContextLen(model, g_ctxLen);
-    const uint32_t blankTokenIdx = 28;
-    arm::app::audio::asr::Postprocess postp(
-                                outputCtxLen,
-                                GetOutputInnerLen(model, outputCtxLen),
-                                blankTokenIdx);
-
     /* Instantiate application context. */
     arm::app::ApplicationContext caseContext;
     std::vector <std::string> labels;
@@ -109,8 +77,6 @@ void main_loop()
     caseContext.Set<uint32_t>("ctxLen", g_ctxLen);  /* Left and right context length (MFCC feat vectors). */
     caseContext.Set<const std::vector <std::string>&>("labels", labels);
     caseContext.Set<arm::app::AsrClassifier&>("classifier", classifier);
-    caseContext.Set<arm::app::audio::asr::Preprocess&>("preprocess", prep);
-    caseContext.Set<arm::app::audio::asr::Postprocess&>("postprocess", postp);
 
     bool executionSuccessful = true;
     constexpr bool bUseMenu = NUMBER_OF_FILES > 1 ? true : false;
@@ -184,52 +150,3 @@ static bool VerifyTensorDimensions(const arm::app::Model& model)
 
     return true;
 }
-
-static uint32_t GetNumMfccFeatures(const arm::app::Model& model)
-{
-    TfLiteTensor* inputTensor = model.GetInputTensor(0);
-    const int inputCols = inputTensor->dims->data[arm::app::Wav2LetterModel::ms_inputColsIdx];
-    if (0 != inputCols % 3) {
-        printf_err("Number of input columns is not a multiple of 3\n");
-    }
-    return std::max(inputCols/3, 0);
-}
-
-static uint32_t GetNumMfccFeatureVectors(const arm::app::Model& model)
-{
-    TfLiteTensor* inputTensor = model.GetInputTensor(0);
-    const int inputRows = inputTensor->dims->data[arm::app::Wav2LetterModel::ms_inputRowsIdx];
-    return std::max(inputRows, 0);
-}
-
-static uint32_t GetOutputContextLen(const arm::app::Model& model, const uint32_t inputCtxLen)
-{
-    const uint32_t inputRows = GetNumMfccFeatureVectors(model);
-    const uint32_t inputInnerLen = inputRows - (2 * inputCtxLen);
-    constexpr uint32_t ms_outputRowsIdx = arm::app::Wav2LetterModel::ms_outputRowsIdx;
-
-    /* Check to make sure that the input tensor supports the above
-     * context and inner lengths. */
-    if (inputRows <= 2 * inputCtxLen || inputRows <= inputInnerLen) {
-        printf_err("Input rows not compatible with ctx of %" PRIu32 "\n",
-            inputCtxLen);
-        return 0;
-    }
-
-    TfLiteTensor* outputTensor = model.GetOutputTensor(0);
-    const uint32_t outputRows = std::max(outputTensor->dims->data[ms_outputRowsIdx], 0);
-
-    const float tensorColRatio = static_cast<float>(inputRows)/
-                                     static_cast<float>(outputRows);
-
-    return std::round(static_cast<float>(inputCtxLen)/tensorColRatio);
-}
-
-static uint32_t GetOutputInnerLen(const arm::app::Model& model,
-                                  const uint32_t outputCtxLen)
-{
-    constexpr uint32_t ms_outputRowsIdx = arm::app::Wav2LetterModel::ms_outputRowsIdx;
-    TfLiteTensor* outputTensor = model.GetOutputTensor(0);
-    const uint32_t outputRows = std::max(outputTensor->dims->data[ms_outputRowsIdx], 0);
-    return (outputRows - (2 * outputCtxLen));
-}
diff --git a/source/use_case/asr/src/UseCaseHandler.cc b/source/use_case/asr/src/UseCaseHandler.cc
index 420f725..7fe959b 100644
--- a/source/use_case/asr/src/UseCaseHandler.cc
+++ b/source/use_case/asr/src/UseCaseHandler.cc
@@ -20,7 +20,6 @@
 #include "AsrClassifier.hpp"
 #include "Wav2LetterModel.hpp"
 #include "hal.h"
-#include "Wav2LetterMfcc.hpp"
 #include "AudioUtils.hpp"
 #include "ImageUtils.hpp"
 #include "UseCaseCommonUtils.hpp"
@@ -34,68 +33,63 @@ namespace arm {
 namespace app {
 
     /**
-     * @brief           Presents inference results using the data presentation
-     *                  object.
-     * @param[in]       results     Vector of classification results to be displayed.
+     * @brief           Presents ASR inference results.
+     * @param[in]       results     Vector of ASR classification results to be displayed.
      * @return          true if successful, false otherwise.
      **/
-    static bool PresentInferenceResult(const std::vector<arm::app::asr::AsrResult>& results);
+    static bool PresentInferenceResult(const std::vector<asr::AsrResult>& results);
 
-    /* Audio inference classification handler. */
+    /* ASR inference handler. */
     bool ClassifyAudioHandler(ApplicationContext& ctx, uint32_t clipIndex, bool runAll)
     {
-        constexpr uint32_t dataPsnTxtInfStartX = 20;
-        constexpr uint32_t dataPsnTxtInfStartY = 40;
-
-        hal_lcd_clear(COLOR_BLACK);
-
+        auto& model = ctx.Get<Model&>("model");
         auto& profiler = ctx.Get<Profiler&>("profiler");
-
+        auto mfccFrameLen = ctx.Get<uint32_t>("frameLength");
+        auto mfccFrameStride = ctx.Get<uint32_t>("frameStride");
+        auto scoreThreshold = ctx.Get<float>("scoreThreshold");
+        auto inputCtxLen = ctx.Get<uint32_t>("ctxLen");
         /* If the request has a valid size, set the audio index. */
         if (clipIndex < NUMBER_OF_FILES) {
             if (!SetAppCtxIfmIdx(ctx, clipIndex,"clipIndex")) {
                 return false;
             }
         }
+        auto initialClipIdx = ctx.Get<uint32_t>("clipIndex");
+        constexpr uint32_t dataPsnTxtInfStartX = 20;
+        constexpr uint32_t dataPsnTxtInfStartY = 40;
 
-        /* Get model reference. */
-        auto& model = ctx.Get<Model&>("model");
         if (!model.IsInited()) {
             printf_err("Model is not initialised! Terminating processing.\n");
             return false;
         }
 
-        /* Get score threshold to be applied for the classifier (post-inference). */
-        auto scoreThreshold = ctx.Get<float>("scoreThreshold");
-
-        /* Get tensors. Dimensions of the tensor should have been verified by
+        /* Get input shape. Dimensions of the tensor should have been verified by
          * the callee. */
-        TfLiteTensor* inputTensor = model.GetInputTensor(0);
-        TfLiteTensor* outputTensor = model.GetOutputTensor(0);
-        const uint32_t inputRows = inputTensor->dims->data[arm::app::Wav2LetterModel::ms_inputRowsIdx];
+        TfLiteIntArray* inputShape = model.GetInputShape(0);
 
-        /* Populate MFCC related parameters. */
-        auto mfccParamsWinLen = ctx.Get<uint32_t>("frameLength");
-        auto mfccParamsWinStride = ctx.Get<uint32_t>("frameStride");
-
-        /* Populate ASR inference context and inner lengths for input. */
-        auto inputCtxLen = ctx.Get<uint32_t>("ctxLen");
-        const uint32_t inputInnerLen = inputRows - (2 * inputCtxLen);
+        const uint32_t inputRowsSize = inputShape->data[Wav2LetterModel::ms_inputRowsIdx];
+        const uint32_t inputInnerLen = inputRowsSize - (2 * inputCtxLen);
 
         /* Audio data stride corresponds to inputInnerLen feature vectors. */
-        const uint32_t audioParamsWinLen = (inputRows - 1) * mfccParamsWinStride + (mfccParamsWinLen);
-        const uint32_t audioParamsWinStride = inputInnerLen * mfccParamsWinStride;
-        const float audioParamsSecondsPerSample = (1.0/audio::Wav2LetterMFCC::ms_defaultSamplingFreq);
+        const uint32_t audioDataWindowLen = (inputRowsSize - 1) * mfccFrameStride + (mfccFrameLen);
+        const uint32_t audioDataWindowStride = inputInnerLen * mfccFrameStride;
+
+        /* NOTE: This is only used for time stamp calculation. */
+        const float secondsPerSample = (1.0 / audio::Wav2LetterMFCC::ms_defaultSamplingFreq);
 
-        /* Get pre/post-processing objects. */
-        auto& prep = ctx.Get<audio::asr::Preprocess&>("preprocess");
-        auto& postp = ctx.Get<audio::asr::Postprocess&>("postprocess");
+        /* Set up pre and post-processing objects. */
+        ASRPreProcess preProcess = ASRPreProcess(model.GetInputTensor(0), Wav2LetterModel::ms_numMfccFeatures,
+                inputShape->data[Wav2LetterModel::ms_inputRowsIdx], mfccFrameLen, mfccFrameStride);
 
-        /* Set default reduction axis for post-processing. */
-        const uint32_t reductionAxis = arm::app::Wav2LetterModel::ms_outputRowsIdx;
+        std::vector<ClassificationResult> singleInfResult;
+        const uint32_t outputCtxLen = ASRPostProcess::GetOutputContextLen(model, inputCtxLen);
+        ASRPostProcess postProcess = ASRPostProcess(ctx.Get<AsrClassifier&>("classifier"),
+                model.GetOutputTensor(0), ctx.Get<std::vector<std::string>&>("labels"),
+                singleInfResult, outputCtxLen,
+                Wav2LetterModel::ms_blankTokenIdx, Wav2LetterModel::ms_outputRowsIdx
+                );
 
-        /* Audio clip start index. */
-        auto startClipIdx = ctx.Get<uint32_t>("clipIndex");
+        UseCaseRunner runner = UseCaseRunner(&preProcess, &postProcess, &model);
 
         /* Loop to process audio clips. */
         do {
@@ -109,44 +103,41 @@ namespace app {
             const uint32_t audioArrSize = get_audio_array_size(currentIndex);
 
             if (!audioArr) {
-                printf_err("Invalid audio array pointer\n");
+                printf_err("Invalid audio array pointer.\n");
                 return false;
             }
 
-            /* Audio clip must have enough samples to produce 1 MFCC feature. */
-            if (audioArrSize < mfccParamsWinLen) {
+            /* Audio clip needs enough samples to produce at least 1 MFCC feature. */
+            if (audioArrSize < mfccFrameLen) {
                 printf_err("Not enough audio samples, minimum needed is %" PRIu32 "\n",
-                    mfccParamsWinLen);
+                           mfccFrameLen);
                 return false;
             }
 
-            /* Initialise an audio slider. */
+            /* Creating a sliding window through the whole audio clip. */
             auto audioDataSlider = audio::FractionalSlidingWindow<const int16_t>(
-                                        audioArr,
-                                        audioArrSize,
-                                        audioParamsWinLen,
-                                        audioParamsWinStride);
+                    audioArr, audioArrSize,
+                    audioDataWindowLen, audioDataWindowStride);
 
-            /* Declare a container for results. */
-            std::vector<arm::app::asr::AsrResult> results;
+            /* Declare a container for final results. */
+            std::vector<asr::AsrResult> finalResults;
 
             /* Display message on the LCD - inference running. */
             std::string str_inf{"Running inference... "};
-            hal_lcd_display_text(
-                                str_inf.c_str(), str_inf.size(),
-                                dataPsnTxtInfStartX, dataPsnTxtInfStartY, 0);
+            hal_lcd_display_text(str_inf.c_str(), str_inf.size(),
+                    dataPsnTxtInfStartX, dataPsnTxtInfStartY, 0);
 
             info("Running inference on audio clip %" PRIu32 " => %s\n", currentIndex,
                  get_filename(currentIndex));
 
-            size_t inferenceWindowLen = audioParamsWinLen;
+            size_t inferenceWindowLen = audioDataWindowLen;
 
             /* Start sliding through audio clip. */
             while (audioDataSlider.HasNext()) {
 
-                /* If not enough audio see how much can be sent for processing. */
+                /* If not enough audio, see how much can be sent for processing. */
                 size_t nextStartIndex = audioDataSlider.NextWindowStartIndex();
-                if (nextStartIndex + audioParamsWinLen > audioArrSize) {
+                if (nextStartIndex + audioDataWindowLen > audioArrSize) {
                     inferenceWindowLen = audioArrSize - nextStartIndex;
                 }
 
@@ -155,46 +146,40 @@ namespace app {
                 info("Inference %zu/%zu\n", audioDataSlider.Index() + 1,
                      static_cast<size_t>(ceilf(audioDataSlider.FractionalTotalStrides() + 1)));
 
-                /* Calculate MFCCs, deltas and populate the input tensor. */
-                prep.Invoke(inferenceWindow, inferenceWindowLen, inputTensor);
+                /* Run the pre-processing, inference and post-processing. */
+                runner.PreProcess(inferenceWindow, inferenceWindowLen);
 
-                /* Run inference over this audio clip sliding window. */
-                if (!RunInference(model, profiler)) {
+                profiler.StartProfiling("Inference");
+                if (!runner.RunInference()) {
                     return false;
                 }
+                profiler.StopProfiling();
 
-                /* Post-process. */
-                postp.Invoke(outputTensor, reductionAxis, !audioDataSlider.HasNext());
-
-                /* Get results. */
-                std::vector<ClassificationResult> classificationResult;
-                auto& classifier = ctx.Get<AsrClassifier&>("classifier");
-                classifier.GetClassificationResults(
-                            outputTensor, classificationResult,
-                            ctx.Get<std::vector<std::string>&>("labels"), 1);
+                postProcess.m_lastIteration = !audioDataSlider.HasNext();
+                if (!runner.PostProcess()) {
+                    return false;
+                }
 
-                results.emplace_back(asr::AsrResult(classificationResult,
-                                                    (audioDataSlider.Index() *
-                                                    audioParamsSecondsPerSample *
-                                                    audioParamsWinStride),
-                                                    audioDataSlider.Index(), scoreThreshold));
+                /* Add results from this window to our final results vector. */
+                finalResults.emplace_back(asr::AsrResult(singleInfResult,
+                        (audioDataSlider.Index() * secondsPerSample * audioDataWindowStride),
+                        audioDataSlider.Index(), scoreThreshold));
 
 #if VERIFY_TEST_OUTPUT
-                arm::app::DumpTensor(outputTensor,
-                    outputTensor->dims->data[arm::app::Wav2LetterModel::ms_outputColsIdx]);
+                TfLiteTensor* outputTensor = model.GetOutputTensor(0);
+                armDumpTensor(outputTensor,
+                    outputTensor->dims->data[Wav2LetterModel::ms_outputColsIdx]);
 #endif /* VERIFY_TEST_OUTPUT */
-
-            }
+            } /* while (audioDataSlider.HasNext()) */
 
             /* Erase. */
             str_inf = std::string(str_inf.size(), ' ');
-            hal_lcd_display_text(
-                                str_inf.c_str(), str_inf.size(),
-                                dataPsnTxtInfStartX, dataPsnTxtInfStartY, 0);
+            hal_lcd_display_text(str_inf.c_str(), str_inf.size(),
+                    dataPsnTxtInfStartX, dataPsnTxtInfStartY, 0);
 
-            ctx.Set<std::vector<arm::app::asr::AsrResult>>("results", results);
+            ctx.Set<std::vector<asr::AsrResult>>("results", finalResults);
 
-            if (!PresentInferenceResult(results)) {
+            if (!PresentInferenceResult(finalResults)) {
                 return false;
             }
 
@@ -202,13 +187,13 @@ namespace app {
 
             IncrementAppCtxIfmIdx(ctx,"clipIndex");
 
-        } while (runAll && ctx.Get<uint32_t>("clipIndex") != startClipIdx);
+        } while (runAll && ctx.Get<uint32_t>("clipIndex") != initialClipIdx);
 
         return true;
     }
 
 
-    static bool PresentInferenceResult(const std::vector<arm::app::asr::AsrResult>& results)
+    static bool PresentInferenceResult(const std::vector<asr::AsrResult>& results)
     {
         constexpr uint32_t dataPsnTxtStartX1 = 20;
         constexpr uint32_t dataPsnTxtStartY1 = 60;
@@ -219,15 +204,15 @@ namespace app {
         info("Final results:\n");
         info("Total number of inferences: %zu\n", results.size());
         /* Results from multiple inferences should be combined before processing. */
-        std::vector<arm::app::ClassificationResult> combinedResults;
-        for (auto& result : results) {
+        std::vector<ClassificationResult> combinedResults;
+        for (const auto& result : results) {
             combinedResults.insert(combinedResults.end(),
                                    result.m_resultVec.begin(),
                                    result.m_resultVec.end());
         }
 
         /* Get each inference result string using the decoder. */
-        for (const auto & result : results) {
+        for (const auto& result : results) {
             std::string infResultStr = audio::asr::DecodeOutput(result.m_resultVec);
 
             info("For timestamp: %f (inference #: %" PRIu32 "); label: %s\n",
@@ -238,10 +223,9 @@ namespace app {
         /* Get the decoded result for the combined result. */
         std::string finalResultStr = audio::asr::DecodeOutput(combinedResults);
 
-        hal_lcd_display_text(
-                            finalResultStr.c_str(), finalResultStr.size(),
-                            dataPsnTxtStartX1, dataPsnTxtStartY1,
-                            allow_multiple_lines);
+        hal_lcd_display_text(finalResultStr.c_str(), finalResultStr.size(),
+                dataPsnTxtStartX1, dataPsnTxtStartY1,
+                allow_multiple_lines);
 
         info("Complete recognition: %s\n", finalResultStr.c_str());
         return true;
diff --git a/source/use_case/asr/src/Wav2LetterMfcc.cc b/source/use_case/asr/src/Wav2LetterMfcc.cc
index 1bcaa66..bb29b0f 100644
--- a/source/use_case/asr/src/Wav2LetterMfcc.cc
+++ b/source/use_case/asr/src/Wav2LetterMfcc.cc
@@ -15,6 +15,7 @@
  * limitations under the License.
  */
 #include "Wav2LetterMfcc.hpp"
+
 #include "PlatformMath.hpp"
 #include "log_macros.h"
 
diff --git a/source/use_case/asr/src/Wav2LetterModel.cc b/source/use_case/asr/src/Wav2LetterModel.cc
index 766bce9..8b38f4f 100644
--- a/source/use_case/asr/src/Wav2LetterModel.cc
+++ b/source/use_case/asr/src/Wav2LetterModel.cc
@@ -15,6 +15,7 @@
  * limitations under the License.
  */
 #include "Wav2LetterModel.hpp"
+
 #include "log_macros.h"
 
 
diff --git a/source/use_case/asr/src/Wav2LetterPostprocess.cc b/source/use_case/asr/src/Wav2LetterPostprocess.cc
index 0392061..e3e1999 100644
--- a/source/use_case/asr/src/Wav2LetterPostprocess.cc
+++ b/source/use_case/asr/src/Wav2LetterPostprocess.cc
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021 Arm Limited. All rights reserved.
+ * Copyright (c) 2021-2022 Arm Limited. All rights reserved.
  * SPDX-License-Identifier: Apache-2.0
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
@@ -15,67 +15,71 @@
  * limitations under the License.
  */
 #include "Wav2LetterPostprocess.hpp"
+
 #include "Wav2LetterModel.hpp"
 #include "log_macros.h"
 
+#include <cmath>
+
 namespace arm {
 namespace app {
-namespace audio {
-namespace asr {
-
-    Postprocess::Postprocess(const uint32_t contextLen,
-                             const uint32_t innerLen,
-                             const uint32_t blankTokenIdx)
-        :   m_contextLen(contextLen),
-            m_innerLen(innerLen),
-            m_totalLen(2 * this->m_contextLen + this->m_innerLen),
+
+    ASRPostProcess::ASRPostProcess(AsrClassifier& classifier, TfLiteTensor* outputTensor,
+            const std::vector<std::string>& labels, std::vector<ClassificationResult>& results,
+            const uint32_t outputContextLen,
+            const uint32_t blankTokenIdx, const uint32_t reductionAxisIdx
+            ):
+            m_classifier(classifier),
+            m_outputTensor(outputTensor),
+            m_labels{labels},
+            m_results(results),
+            m_outputContextLen(outputContextLen),
             m_countIterations(0),
-            m_blankTokenIdx(blankTokenIdx)
-    {}
+            m_blankTokenIdx(blankTokenIdx),
+            m_reductionAxisIdx(reductionAxisIdx)
+    {
+        this->m_outputInnerLen = ASRPostProcess::GetOutputInnerLen(this->m_outputTensor, this->m_outputContextLen);
+        this->m_totalLen = (2 * this->m_outputContextLen + this->m_outputInnerLen);
+    }
 
-    bool Postprocess::Invoke(TfLiteTensor*  tensor,
-                            const uint32_t  axisIdx,
-                            const bool      lastIteration)
+    bool ASRPostProcess::DoPostProcess()
     {
         /* Basic checks. */
-        if (!this->IsInputValid(tensor, axisIdx)) {
+        if (!this->IsInputValid(this->m_outputTensor, this->m_reductionAxisIdx)) {
             return false;
         }
 
         /* Irrespective of tensor type, we use unsigned "byte" */
-        uint8_t* ptrData = tflite::GetTensorData<uint8_t>(tensor);
-        const uint32_t elemSz = this->GetTensorElementSize(tensor);
+        auto* ptrData = tflite::GetTensorData<uint8_t>(this->m_outputTensor);
+        const uint32_t elemSz = ASRPostProcess::GetTensorElementSize(this->m_outputTensor);
 
         /* Other sanity checks. */
         if (0 == elemSz) {
             printf_err("Tensor type not supported for post processing\n");
             return false;
-        } else if (elemSz * this->m_totalLen > tensor->bytes) {
+        } else if (elemSz * this->m_totalLen > this->m_outputTensor->bytes) {
             printf_err("Insufficient number of tensor bytes\n");
             return false;
         }
 
         /* Which axis do we need to process? */
-        switch (axisIdx) {
-            case arm::app::Wav2LetterModel::ms_outputRowsIdx:
-                return this->EraseSectionsRowWise(ptrData,
-                                                  elemSz *
-                                                  tensor->dims->data[arm::app::Wav2LetterModel::ms_outputColsIdx],
-                                                  lastIteration);
-            case arm::app::Wav2LetterModel::ms_outputColsIdx:
-                return this->EraseSectionsColWise(ptrData,
-                                                  elemSz *
-                                                  tensor->dims->data[arm::app::Wav2LetterModel::ms_outputRowsIdx],
-                                                  lastIteration);
+        switch (this->m_reductionAxisIdx) {
+            case Wav2LetterModel::ms_outputRowsIdx:
+                this->EraseSectionsRowWise(
+                        ptrData, elemSz * this->m_outputTensor->dims->data[Wav2LetterModel::ms_outputColsIdx],
+                        this->m_lastIteration);
+                break;
             default:
-                printf_err("Unsupported axis index: %" PRIu32 "\n", axisIdx);
+                printf_err("Unsupported axis index: %" PRIu32 "\n", this->m_reductionAxisIdx);
+                return false;
         }
+        this->m_classifier.GetClassificationResults(this->m_outputTensor,
+                this->m_results, this->m_labels, 1);
 
-        return false;
+        return true;
     }
 
-    bool Postprocess::IsInputValid(TfLiteTensor*  tensor,
-                                   const uint32_t axisIdx) const
+    bool ASRPostProcess::IsInputValid(TfLiteTensor* tensor, const uint32_t axisIdx) const
     {
         if (nullptr == tensor) {
             return false;
@@ -89,15 +93,15 @@ namespace asr {
 
         if (static_cast<int>(this->m_totalLen) !=
                              tensor->dims->data[axisIdx]) {
-            printf_err("Unexpected tensor dimension for axis %d, \n",
-                tensor->dims->data[axisIdx]);
+            printf_err("Unexpected tensor dimension for axis %d, got %d, \n",
+                axisIdx, tensor->dims->data[axisIdx]);
             return false;
         }
 
         return true;
     }
 
-    uint32_t Postprocess::GetTensorElementSize(TfLiteTensor*  tensor)
+    uint32_t ASRPostProcess::GetTensorElementSize(TfLiteTensor* tensor)
     {
         switch(tensor->type) {
             case kTfLiteUInt8:
@@ -116,30 +120,30 @@ namespace asr {
         return 0;
     }
 
-    bool Postprocess::EraseSectionsRowWise(
-                        uint8_t*         ptrData,
-                        const uint32_t   strideSzBytes,
-                        const bool       lastIteration)
+    bool ASRPostProcess::EraseSectionsRowWise(
+            uint8_t*         ptrData,
+            const uint32_t   strideSzBytes,
+            const bool       lastIteration)
     {
         /* In this case, the "zero-ing" is quite simple as the region
          * to be zeroed sits in contiguous memory (row-major). */
-        const uint32_t eraseLen = strideSzBytes * this->m_contextLen;
+        const uint32_t eraseLen = strideSzBytes * this->m_outputContextLen;
 
         /* Erase left context? */
         if (this->m_countIterations > 0) {
             /* Set output of each classification window to the blank token. */
             std::memset(ptrData, 0, eraseLen);
-            for (size_t windowIdx = 0; windowIdx < this->m_contextLen; windowIdx++) {
+            for (size_t windowIdx = 0; windowIdx < this->m_outputContextLen; windowIdx++) {
                 ptrData[windowIdx*strideSzBytes + this->m_blankTokenIdx] = 1;
             }
         }
 
         /* Erase right context? */
         if (false == lastIteration) {
-            uint8_t * rightCtxPtr = ptrData + (strideSzBytes * (this->m_contextLen + this->m_innerLen));
+            uint8_t* rightCtxPtr = ptrData + (strideSzBytes * (this->m_outputContextLen + this->m_outputInnerLen));
             /* Set output of each classification window to the blank token. */
             std::memset(rightCtxPtr, 0, eraseLen);
-            for (size_t windowIdx = 0; windowIdx < this->m_contextLen; windowIdx++) {
+            for (size_t windowIdx = 0; windowIdx < this->m_outputContextLen; windowIdx++) {
                 rightCtxPtr[windowIdx*strideSzBytes + this->m_blankTokenIdx] = 1;
             }
         }
@@ -153,19 +157,56 @@ namespace asr {
         return true;
     }
 
-    bool Postprocess::EraseSectionsColWise(
-                        const uint8_t*         ptrData,
-                        const uint32_t   strideSzBytes,
-                        const bool       lastIteration)
+    uint32_t ASRPostProcess::GetNumFeatureVectors(const Model& model)
+    {
+        TfLiteTensor* inputTensor = model.GetInputTensor(0);
+        const int inputRows = std::max(inputTensor->dims->data[Wav2LetterModel::ms_inputRowsIdx], 0);
+        if (inputRows == 0) {
+            printf_err("Error getting number of input rows for axis: %" PRIu32 "\n",
+                    Wav2LetterModel::ms_inputRowsIdx);
+        }
+        return inputRows;
+    }
+
+    uint32_t ASRPostProcess::GetOutputInnerLen(const TfLiteTensor* outputTensor, const uint32_t outputCtxLen)
     {
-        /* Not implemented. */
-        UNUSED(ptrData);
-        UNUSED(strideSzBytes);
-        UNUSED(lastIteration);
-        return false;
+        const uint32_t outputRows = std::max(outputTensor->dims->data[Wav2LetterModel::ms_outputRowsIdx], 0);
+        if (outputRows == 0) {
+            printf_err("Error getting number of output rows for axis: %" PRIu32 "\n",
+                    Wav2LetterModel::ms_outputRowsIdx);
+        }
+        int innerLen = (outputRows - (2 * outputCtxLen));
+
+        return std::max(innerLen, 0);
+    }
+
+    uint32_t ASRPostProcess::GetOutputContextLen(const Model& model, const uint32_t inputCtxLen)
+    {
+        const uint32_t inputRows = ASRPostProcess::GetNumFeatureVectors(model);
+        const uint32_t inputInnerLen = inputRows - (2 * inputCtxLen);
+        constexpr uint32_t ms_outputRowsIdx = Wav2LetterModel::ms_outputRowsIdx;
+
+        /* Check to make sure that the input tensor supports the above
+         * context and inner lengths. */
+        if (inputRows <= 2 * inputCtxLen || inputRows <= inputInnerLen) {
+            printf_err("Input rows not compatible with ctx of %" PRIu32 "\n",
+                       inputCtxLen);
+            return 0;
+        }
+
+        TfLiteTensor* outputTensor = model.GetOutputTensor(0);
+        const uint32_t outputRows = std::max(outputTensor->dims->data[ms_outputRowsIdx], 0);
+        if (outputRows == 0) {
+            printf_err("Error getting number of output rows for axis: %" PRIu32 "\n",
+                       Wav2LetterModel::ms_outputRowsIdx);
+            return 0;
+        }
+
+        const float inOutRowRatio = static_cast<float>(inputRows) /
+                                     static_cast<float>(outputRows);
+
+        return std::round(static_cast<float>(inputCtxLen) / inOutRowRatio);
     }
 
-} /* namespace asr */
-} /* namespace audio */
 } /* namespace app */
 } /* namespace arm */
\ No newline at end of file
diff --git a/source/use_case/asr/src/Wav2LetterPreprocess.cc b/source/use_case/asr/src/Wav2LetterPreprocess.cc
index e5ac3ca..590d08a 100644
--- a/source/use_case/asr/src/Wav2LetterPreprocess.cc
+++ b/source/use_case/asr/src/Wav2LetterPreprocess.cc
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021 Arm Limited. All rights reserved.
+ * Copyright (c) 2021-2022 Arm Limited. All rights reserved.
  * SPDX-License-Identifier: Apache-2.0
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
@@ -24,37 +24,31 @@
 
 namespace arm {
 namespace app {
-namespace audio {
-namespace asr {
-
-    Preprocess::Preprocess(
-        const uint32_t  numMfccFeatures,
-        const uint32_t  windowLen,
-        const uint32_t  windowStride,
-        const uint32_t  numMfccVectors):
-            m_mfcc(numMfccFeatures, windowLen),
-            m_mfccBuf(numMfccFeatures, numMfccVectors),
-            m_delta1Buf(numMfccFeatures, numMfccVectors),
-            m_delta2Buf(numMfccFeatures, numMfccVectors),
-            m_windowLen(windowLen),
-            m_windowStride(windowStride),
+
+    ASRPreProcess::ASRPreProcess(TfLiteTensor* inputTensor, const uint32_t numMfccFeatures,
+            const uint32_t numFeatureFrames, const uint32_t mfccWindowLen,
+            const uint32_t mfccWindowStride
+            ):
+            m_mfcc(numMfccFeatures, mfccWindowLen),
+            m_inputTensor(inputTensor),
+            m_mfccBuf(numMfccFeatures, numFeatureFrames),
+            m_delta1Buf(numMfccFeatures, numFeatureFrames),
+            m_delta2Buf(numMfccFeatures, numFeatureFrames),
+            m_mfccWindowLen(mfccWindowLen),
+            m_mfccWindowStride(mfccWindowStride),
             m_numMfccFeats(numMfccFeatures),
-            m_numFeatVectors(numMfccVectors),
-            m_window()
+            m_numFeatureFrames(numFeatureFrames)
     {
-        if (numMfccFeatures > 0 && windowLen > 0) {
+        if (numMfccFeatures > 0 && mfccWindowLen > 0) {
             this->m_mfcc.Init();
         }
     }
 
-    bool Preprocess::Invoke(
-                const int16_t*  audioData,
-                const uint32_t  audioDataLen,
-                TfLiteTensor*   tensor)
+    bool ASRPreProcess::DoPreProcess(const void* audioData, const size_t audioDataLen)
     {
-        this->m_window = SlidingWindow<const int16_t>(
-                            audioData, audioDataLen,
-                            this->m_windowLen, this->m_windowStride);
+        this->m_mfccSlidingWindow = audio::SlidingWindow<const int16_t>(
+                static_cast<const int16_t*>(audioData), audioDataLen,
+                this->m_mfccWindowLen, this->m_mfccWindowStride);
 
         uint32_t mfccBufIdx = 0;
 
@@ -62,12 +56,12 @@ namespace asr {
         std::fill(m_delta1Buf.begin(), m_delta1Buf.end(), 0.f);
         std::fill(m_delta2Buf.begin(), m_delta2Buf.end(), 0.f);
 
-        /* While we can slide over the window. */
-        while (this->m_window.HasNext()) {
-            const int16_t*  mfccWindow = this->m_window.Next();
+        /* While we can slide over the audio. */
+        while (this->m_mfccSlidingWindow.HasNext()) {
+            const int16_t* mfccWindow = this->m_mfccSlidingWindow.Next();
             auto mfccAudioData = std::vector<int16_t>(
                                         mfccWindow,
-                                        mfccWindow + this->m_windowLen);
+                                        mfccWindow + this->m_mfccWindowLen);
             auto mfcc = this->m_mfcc.MfccCompute(mfccAudioData);
             for (size_t i = 0; i < this->m_mfccBuf.size(0); ++i) {
                 this->m_mfccBuf(i, mfccBufIdx) = mfcc[i];
@@ -76,11 +70,11 @@ namespace asr {
         }
 
         /* Pad MFCC if needed by adding MFCC for zeros. */
-        if (mfccBufIdx != this->m_numFeatVectors) {
-            std::vector<int16_t> zerosWindow = std::vector<int16_t>(this->m_windowLen, 0);
+        if (mfccBufIdx != this->m_numFeatureFrames) {
+            std::vector<int16_t> zerosWindow = std::vector<int16_t>(this->m_mfccWindowLen, 0);
             std::vector<float> mfccZeros = this->m_mfcc.MfccCompute(zerosWindow);
 
-            while (mfccBufIdx != this->m_numFeatVectors) {
+            while (mfccBufIdx != this->m_numFeatureFrames) {
                 memcpy(&this->m_mfccBuf(0, mfccBufIdx),
                        mfccZeros.data(), sizeof(float) * m_numMfccFeats);
                 ++mfccBufIdx;
@@ -88,39 +82,37 @@ namespace asr {
         }
 
         /* Compute first and second order deltas from MFCCs. */
-        Preprocess::ComputeDeltas(this->m_mfccBuf,
-                            this->m_delta1Buf,
-                            this->m_delta2Buf);
+        ASRPreProcess::ComputeDeltas(this->m_mfccBuf, this->m_delta1Buf, this->m_delta2Buf);
 
-        /* Normalise. */
-        this->Normalise();
+        /* Standardize calculated features. */
+        this->Standarize();
 
         /* Quantise. */
-        QuantParams quantParams = GetTensorQuantParams(tensor);
+        QuantParams quantParams = GetTensorQuantParams(this->m_inputTensor);
 
         if (0 == quantParams.scale) {
             printf_err("Quantisation scale can't be 0\n");
             return false;
         }
 
-        switch(tensor->type) {
+        switch(this->m_inputTensor->type) {
             case kTfLiteUInt8:
                 return this->Quantise<uint8_t>(
-                        tflite::GetTensorData<uint8_t>(tensor), tensor->bytes,
+                        tflite::GetTensorData<uint8_t>(this->m_inputTensor), this->m_inputTensor->bytes,
                         quantParams.scale, quantParams.offset);
             case kTfLiteInt8:
                 return this->Quantise<int8_t>(
-                        tflite::GetTensorData<int8_t>(tensor), tensor->bytes,
+                        tflite::GetTensorData<int8_t>(this->m_inputTensor), this->m_inputTensor->bytes,
                         quantParams.scale, quantParams.offset);
             default:
                 printf_err("Unsupported tensor type %s\n",
-                    TfLiteTypeGetName(tensor->type));
+                    TfLiteTypeGetName(this->m_inputTensor->type));
         }
 
         return false;
     }
 
-    bool Preprocess::ComputeDeltas(Array2d<float>& mfcc,
+    bool ASRPreProcess::ComputeDeltas(Array2d<float>& mfcc,
                                    Array2d<float>& delta1,
                                    Array2d<float>& delta2)
     {
@@ -175,20 +167,10 @@ namespace asr {
         return true;
     }
 
-    float Preprocess::GetMean(Array2d<float>& vec)
-    {
-        return math::MathUtils::MeanF32(vec.begin(), vec.totalSize());
-    }
-
-    float Preprocess::GetStdDev(Array2d<float>& vec, const float mean)
-    {
-        return math::MathUtils::StdDevF32(vec.begin(), vec.totalSize(), mean);
-    }
-
-    void Preprocess::NormaliseVec(Array2d<float>& vec)
+    void ASRPreProcess::StandardizeVecF32(Array2d<float>& vec)
     {
-        auto mean = Preprocess::GetMean(vec);
-        auto stddev = Preprocess::GetStdDev(vec, mean);
+        auto mean = math::MathUtils::MeanF32(vec.begin(), vec.totalSize());
+        auto stddev = math::MathUtils::StdDevF32(vec.begin(), vec.totalSize(), mean);
 
         debug("Mean: %f, Stddev: %f\n", mean, stddev);
         if (stddev == 0) {
@@ -204,14 +186,14 @@ namespace asr {
         }
     }
 
-    void Preprocess::Normalise()
+    void ASRPreProcess::Standarize()
     {
-        Preprocess::NormaliseVec(this->m_mfccBuf);
-        Preprocess::NormaliseVec(this->m_delta1Buf);
-        Preprocess::NormaliseVec(this->m_delta2Buf);
+        ASRPreProcess::StandardizeVecF32(this->m_mfccBuf);
+        ASRPreProcess::StandardizeVecF32(this->m_delta1Buf);
+        ASRPreProcess::StandardizeVecF32(this->m_delta2Buf);
     }
 
-    float Preprocess::GetQuantElem(
+    float ASRPreProcess::GetQuantElem(
                 const float     elem,
                 const float     quantScale,
                 const int       quantOffset,
@@ -222,7 +204,5 @@ namespace asr {
         return std::min<float>(std::max<float>(val, minVal), maxVal);
     }
 
-} /* namespace asr */
-} /* namespace audio */
 } /* namespace app */
 } /* namespace arm */
\ No newline at end of file
diff --git a/source/use_case/kws/include/KwsProcessing.hpp b/source/use_case/kws/include/KwsProcessing.hpp
index abf20ab..ddf38c1 100644
--- a/source/use_case/kws/include/KwsProcessing.hpp
+++ b/source/use_case/kws/include/KwsProcessing.hpp
@@ -38,7 +38,7 @@ namespace app {
     public:
         /**
          * @brief       Constructor
-         * @param[in]   model             Pointer to the the KWS Model object.
+         * @param[in]   model             Pointer to the KWS Model object.
          * @param[in]   numFeatures       How many MFCC features to use.
          * @param[in]   mfccFrameLength   Number of audio samples used to calculate one set of MFCC values when
          *                                sliding a window through the audio sample.
@@ -107,24 +107,21 @@ namespace app {
         std::vector<ClassificationResult>& m_results;
 
     public:
-        const float m_scoreThreshold;
         /**
-         * @brief       Constructor
-         * @param[in]   classifier       Classifier object used to get top N results from classification.
-         * @param[in]   model            Pointer to the the Image classification Model object.
-         * @param[in]   labels           Vector of string labels to identify each output of the model.
-         * @param[in]   results          Vector of classification results to store decoded outputs.
-         * @param[in]   scoreThreshold   Predicted model score must be larger than this value to be accepted.
+         * @brief           Constructor
+         * @param[in]       classifier   Classifier object used to get top N results from classification.
+         * @param[in]       model        Pointer to the KWS Model object.
+         * @param[in]       labels       Vector of string labels to identify each output of the model.
+         * @param[in/out]   results      Vector of classification results to store decoded outputs.
          **/
         KWSPostProcess(Classifier& classifier, Model* model,
                        const std::vector<std::string>& labels,
-                       std::vector<ClassificationResult>& results,
-                       float scoreThreshold);
+                       std::vector<ClassificationResult>& results);
 
         /**
-         * @brief       Should perform post-processing of the result of inference then populate
-         *              populate KWS result data for any later use.
-         * @return      true if successful, false otherwise.
+         * @brief    Should perform post-processing of the result of inference then
+         *           populate KWS result data for any later use.
+         * @return   true if successful, false otherwise.
          **/
         bool DoPostProcess() override;
     };
diff --git a/source/use_case/kws/src/KwsProcessing.cc b/source/use_case/kws/src/KwsProcessing.cc
index b6b230c..14f9fce 100644
--- a/source/use_case/kws/src/KwsProcessing.cc
+++ b/source/use_case/kws/src/KwsProcessing.cc
@@ -197,11 +197,10 @@ namespace app {
 
     KWSPostProcess::KWSPostProcess(Classifier& classifier, Model* model,
                                    const std::vector<std::string>& labels,
-                                   std::vector<ClassificationResult>& results, float scoreThreshold)
+                                   std::vector<ClassificationResult>& results)
             :m_kwsClassifier{classifier},
              m_labels{labels},
-             m_results{results},
-             m_scoreThreshold{scoreThreshold}
+             m_results{results}
     {
         if (!model->IsInited()) {
             printf_err("Model is not initialised!.\n");
diff --git a/source/use_case/kws/src/UseCaseHandler.cc b/source/use_case/kws/src/UseCaseHandler.cc
index 350d34b..e73a2c3 100644
--- a/source/use_case/kws/src/UseCaseHandler.cc
+++ b/source/use_case/kws/src/UseCaseHandler.cc
@@ -93,7 +93,7 @@ namespace app {
         std::vector<ClassificationResult> singleInfResult;
         KWSPostProcess postprocess = KWSPostProcess(ctx.Get<KwsClassifier &>("classifier"), &model,
                                                     ctx.Get<std::vector<std::string>&>("labels"),
-                                                    singleInfResult, scoreThreshold);
+                                                    singleInfResult);
 
         UseCaseRunner runner = UseCaseRunner(&preprocess, &postprocess, &model);
 
@@ -146,7 +146,7 @@ namespace app {
                 /* Add results from this window to our final results vector. */
                 finalResults.emplace_back(kws::KwsResult(singleInfResult,
                         audioDataSlider.Index() * secondsPerSample * preprocess.m_audioDataStride,
-                        audioDataSlider.Index(), postprocess.m_scoreThreshold));
+                        audioDataSlider.Index(), scoreThreshold));
 
 #if VERIFY_TEST_OUTPUT
                 TfLiteTensor* outputTensor = model.GetOutputTensor(0);
diff --git a/tests/common/PlatformMathTests.cpp b/tests/common/PlatformMathTests.cpp
index ab1153f..c07cbf1 100644
--- a/tests/common/PlatformMathTests.cpp
+++ b/tests/common/PlatformMathTests.cpp
@@ -150,13 +150,28 @@ TEST_CASE("Test SqrtF32")
 
 TEST_CASE("Test MeanF32")
 {
-    /*Test  Constants: */
+    /* Test Constants: */
     std::vector<float> input
         {0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 1.000};
 
     /* Manually calculated mean of above vector */
     float expectedResult = 0.100;
     CHECK (expectedResult == Approx(arm::app::math::MathUtils::MeanF32(input.data(), input.size())));
+
+    /* Mean of 0 */
+    std::vector<float> input2{1, 2, -1, -2};
+    float expectedResult2 = 0.0f;
+    CHECK (expectedResult2 == Approx(arm::app::math::MathUtils::MeanF32(input2.data(), input2.size())));
+
+    /* All 0s */
+    std::vector<float> input3 = std::vector<float>(9, 0);
+    float expectedResult3 = 0.0f;
+    CHECK (expectedResult3 == Approx(arm::app::math::MathUtils::MeanF32(input3.data(), input3.size())));
+
+    /* All 1s */
+    std::vector<float> input4 = std::vector<float>(9, 1);
+    float expectedResult4 = 1.0f;
+    CHECK (expectedResult4 == Approx(arm::app::math::MathUtils::MeanF32(input4.data(), input4.size())));
 }
 
 TEST_CASE("Test StdDevF32")
@@ -184,6 +199,22 @@ TEST_CASE("Test StdDevF32")
     float expectedResult = 0.969589282958136;
 
     CHECK (expectedResult == Approx(output));
+
+    /* All 0s should have 0 std dev. */
+    std::vector<float> input2 = std::vector<float>(4, 0);
+    float expectedResult2 = 0.0f;
+    CHECK (expectedResult2 == Approx(arm::app::math::MathUtils::StdDevF32(input2.data(), input2.size(), 0.0f)));
+
+    /* All 1s should have 0 std dev. */
+    std::vector<float> input3 = std::vector<float>(4, 1);
+    float expectedResult3 = 0.0f;
+    CHECK (expectedResult3 == Approx(arm::app::math::MathUtils::StdDevF32(input3.data(), input3.size(), 1.0f)));
+
+    /* Manually calclualted std value */
+    std::vector<float> input4 {1, 2, 3, 4, 5, 6, 7, 8, 9, 0};
+    float mean2 = (std::accumulate(input4.begin(), input4.end(), 0.0f))/float(input4.size());
+    float expectedResult4 = 2.872281323;
+    CHECK (expectedResult4 == Approx(arm::app::math::MathUtils::StdDevF32(input4.data(), input4.size(), mean2)));
 }
 
 TEST_CASE("Test FFT32")
diff --git a/tests/use_case/asr/AsrFeaturesTests.cc b/tests/use_case/asr/AsrFeaturesTests.cc
index 940c25f..6c23598 100644
--- a/tests/use_case/asr/AsrFeaturesTests.cc
+++ b/tests/use_case/asr/AsrFeaturesTests.cc
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021 Arm Limited. All rights reserved.
+ * Copyright (c) 2021-2022 Arm Limited. All rights reserved.
  * SPDX-License-Identifier: Apache-2.0
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
@@ -23,29 +23,19 @@
 #include <catch.hpp>
 #include <random>
 
-class TestPreprocess : public arm::app::audio::asr::Preprocess {
+class TestPreprocess : public arm::app::ASRPreProcess {
 public:
 
     static bool ComputeDeltas(arm::app::Array2d<float>& mfcc,
                        arm::app::Array2d<float>& delta1,
                        arm::app::Array2d<float>& delta2)
     {
-        return Preprocess::ComputeDeltas(mfcc, delta1, delta2);
-    }
-
-    static float GetMean(arm::app::Array2d<float>& vec)
-    {
-        return Preprocess::GetMean(vec);
-    }
-
-    static float GetStdDev(arm::app::Array2d<float>& vec, const float mean)
-    {
-       return Preprocess::GetStdDev(vec, mean);
+        return ASRPreProcess::ComputeDeltas(mfcc, delta1, delta2);
     }
 
     static void NormaliseVec(arm::app::Array2d<float>& vec)
     {
-        return Preprocess::NormaliseVec(vec);
+        return ASRPreProcess::StandardizeVecF32(vec);
     }
 };
 
@@ -126,40 +116,6 @@ TEST_CASE("Floating point asr features calculation", "[ASR]")
 
     }
 
-    SECTION("Mean")
-    {
-        std::vector<std::vector<float>> mean1vec{{1, 2},
-                                                {-1, -2}};
-        arm::app::Array2d<float> mean1(2,2); /* {{1, 2},{-1, -2}} */
-        populateArray2dWithVectorOfVector(mean1vec, mean1);
-        REQUIRE(0 == Approx(TestPreprocess::GetMean(mean1)));
-
-        arm::app::Array2d<float> mean2(2, 2);
-        std::fill(mean2.begin(), mean2.end(), 0.f);
-        REQUIRE(0 == Approx(TestPreprocess::GetMean(mean2)));
-
-        arm::app::Array2d<float> mean3(3,3);
-        std::fill(mean3.begin(), mean3.end(), 1.f);
-        REQUIRE(1 == Approx(TestPreprocess::GetMean(mean3)));
-    }
-
-    SECTION("Std")
-    {
-        arm::app::Array2d<float> std1(2, 2);
-        std::fill(std1.begin(), std1.end(), 0.f); /* {{0, 0}, {0, 0}} */
-        REQUIRE(0 == Approx(TestPreprocess::GetStdDev(std1, 0)));
-
-        std::vector<std::vector<float>> std2vec{{1, 2, 3, 4, 5}, {6, 7, 8, 9, 0}};
-        arm::app::Array2d<float> std2(2,5);
-        populateArray2dWithVectorOfVector(std2vec, std2);
-        const float mean = TestPreprocess::GetMean(std2);
-        REQUIRE(2.872281323 == Approx(TestPreprocess::GetStdDev(std2, mean)));
-
-        arm::app::Array2d<float> std3(2,2);
-        std::fill(std3.begin(), std3.end(), 1.f); /* std3{{1, 1}, {1, 1}}; */
-        REQUIRE(0 == Approx(TestPreprocess::GetStdDev(std3, 1)));
-    }
-
     SECTION("Norm") {
         auto checker = [&](arm::app::Array2d<float>& d, std::vector<float>& g) {
             TestPreprocess::NormaliseVec(d);
diff --git a/tests/use_case/asr/Wav2LetterPostprocessingTest.cc b/tests/use_case/asr/Wav2LetterPostprocessingTest.cc
index 9ed2e1b..d0b6505 100644
--- a/tests/use_case/asr/Wav2LetterPostprocessingTest.cc
+++ b/tests/use_case/asr/Wav2LetterPostprocessingTest.cc
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021 Arm Limited. All rights reserved.
+ * Copyright (c) 2021-2022 Arm Limited. All rights reserved.
  * SPDX-License-Identifier: Apache-2.0
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
@@ -16,6 +16,7 @@
  */
 #include "Wav2LetterPostprocess.hpp"
 #include "Wav2LetterModel.hpp"
+#include "ClassificationResult.hpp"
 
 #include <algorithm>
 #include <catch.hpp>
@@ -47,85 +48,105 @@ TEST_CASE("Checking return value")
 {
     SECTION("Mismatched post processing parameters and tensor size")
     {
-        const uint32_t ctxLen = 5;
-        const uint32_t innerLen = 3;
-        arm::app::audio::asr::Postprocess post{ctxLen, innerLen, 0};
-
+        const uint32_t outputCtxLen = 5;
+        arm::app::AsrClassifier classifier;
+        arm::app::Wav2LetterModel model;
+        model.Init();
+        std::vector<std::string> dummyLabels = {"a", "b", "$"};
+        const uint32_t blankTokenIdx = 2;
+        std::vector<arm::app::ClassificationResult> dummyResult;
         std::vector <int> tensorShape = {1, 1, 1, 13};
         std::vector <int8_t> tensorVec;
         TfLiteTensor tensor = GetTestTensor<int8_t>(
-                                tensorShape, 100, tensorVec);
-        REQUIRE(false == post.Invoke(&tensor, arm::app::Wav2LetterModel::ms_outputRowsIdx, false));
+                tensorShape, 100, tensorVec);
+
+        arm::app::ASRPostProcess post{classifier, &tensor, dummyLabels, dummyResult, outputCtxLen,
+                                      blankTokenIdx, arm::app::Wav2LetterModel::ms_outputRowsIdx};
+
+        REQUIRE(!post.DoPostProcess());
     }
 
     SECTION("Post processing succeeds")
     {
-        const uint32_t ctxLen = 5;
-        const uint32_t innerLen = 3;
-        arm::app::audio::asr::Postprocess post{ctxLen, innerLen, 0};
-
-        std::vector <int> tensorShape = {1, 1, 13, 1};
-        std::vector <int8_t> tensorVec;
+        const uint32_t outputCtxLen = 5;
+        arm::app::AsrClassifier classifier;
+        arm::app::Wav2LetterModel model;
+        model.Init();
+        std::vector<std::string> dummyLabels = {"a", "b", "$"};
+        const uint32_t blankTokenIdx = 2;
+        std::vector<arm::app::ClassificationResult> dummyResult;
+        std::vector<int> tensorShape = {1, 1, 13, 1};
+        std::vector<int8_t> tensorVec;
         TfLiteTensor tensor = GetTestTensor<int8_t>(
-                                tensorShape, 100, tensorVec);
+                tensorShape, 100, tensorVec);
+
+        arm::app::ASRPostProcess post{classifier, &tensor, dummyLabels, dummyResult, outputCtxLen,
+                                      blankTokenIdx, arm::app::Wav2LetterModel::ms_outputRowsIdx};
 
         /* Copy elements to compare later. */
-        std::vector <int8_t> originalVec = tensorVec;
+        std::vector<int8_t> originalVec = tensorVec;
 
         /* This step should not erase anything. */
-        REQUIRE(true == post.Invoke(&tensor, arm::app::Wav2LetterModel::ms_outputRowsIdx, false));
+        REQUIRE(post.DoPostProcess());
     }
 }
 
 
 TEST_CASE("Postprocessing - erasing required elements")
 {
-    constexpr uint32_t ctxLen = 5;
+    constexpr uint32_t outputCtxLen = 5;
     constexpr uint32_t innerLen = 3;
-    constexpr uint32_t nRows = 2*ctxLen + innerLen;
+    constexpr uint32_t nRows = 2*outputCtxLen + innerLen;
     constexpr uint32_t nCols = 10;
     constexpr uint32_t blankTokenIdx = nCols - 1;
-    std::vector <int> tensorShape = {1, 1, nRows, nCols};
+    std::vector<int> tensorShape = {1, 1, nRows, nCols};
+    arm::app::AsrClassifier classifier;
+    arm::app::Wav2LetterModel model;
+    model.Init();
+    std::vector<std::string> dummyLabels = {"a", "b", "$"};
+    std::vector<arm::app::ClassificationResult> dummyResult;
 
     SECTION("First and last iteration")
     {
-        arm::app::audio::asr::Postprocess post{ctxLen, innerLen, blankTokenIdx};
-
-        std::vector <int8_t> tensorVec;
-        TfLiteTensor tensor = GetTestTensor<int8_t>(
-                                tensorShape, 100, tensorVec);
+        std::vector<int8_t> tensorVec;
+        TfLiteTensor tensor = GetTestTensor<int8_t>(tensorShape, 100, tensorVec);
+        arm::app::ASRPostProcess post{classifier, &tensor, dummyLabels, dummyResult, outputCtxLen,
+                                      blankTokenIdx, arm::app::Wav2LetterModel::ms_outputRowsIdx};
 
         /* Copy elements to compare later. */
-        std::vector <int8_t> originalVec = tensorVec;
+        std::vector<int8_t>originalVec = tensorVec;
 
         /* This step should not erase anything. */
-        REQUIRE(true == post.Invoke(&tensor, arm::app::Wav2LetterModel::ms_outputRowsIdx, true));
+        post.m_lastIteration = true;
+        REQUIRE(post.DoPostProcess());
         REQUIRE(originalVec == tensorVec);
     }
 
     SECTION("Right context erase")
     {
-        arm::app::audio::asr::Postprocess post{ctxLen, innerLen, blankTokenIdx};
-
         std::vector <int8_t> tensorVec;
         TfLiteTensor tensor = GetTestTensor<int8_t>(
-                                tensorShape, 100, tensorVec);
+                tensorShape, 100, tensorVec);
+        arm::app::ASRPostProcess post{classifier, &tensor, dummyLabels, dummyResult, outputCtxLen,
+                                      blankTokenIdx, arm::app::Wav2LetterModel::ms_outputRowsIdx};
 
         /* Copy elements to compare later. */
-        std::vector <int8_t> originalVec = tensorVec;
+        std::vector<int8_t> originalVec = tensorVec;
 
+        //auto tensorData = tflite::GetTensorData<int8_t>(tensor);
         /* This step should erase the right context only. */
-        REQUIRE(true == post.Invoke(&tensor, arm::app::Wav2LetterModel::ms_outputRowsIdx, false));
+        post.m_lastIteration = false;
+        REQUIRE(post.DoPostProcess());
         REQUIRE(originalVec != tensorVec);
 
         /* The last ctxLen * 10 elements should be gone. */
-        for (size_t i = 0; i < ctxLen; ++i) {
+        for (size_t i = 0; i < outputCtxLen; ++i) {
             for (size_t j = 0; j < nCols; ++j) {
-                /* Check right context elements are zeroed. */
+                /* Check right context elements are zeroed. Blank token idx should be set to 1 when erasing. */
                 if (j == blankTokenIdx) {
-                    CHECK(tensorVec[(ctxLen + innerLen) * nCols + i*nCols + j] == 1);
+                    CHECK(tensorVec[(outputCtxLen + innerLen) * nCols + i*nCols + j] == 1);
                 } else {
-                    CHECK(tensorVec[(ctxLen + innerLen) * nCols + i*nCols + j] == 0);
+                    CHECK(tensorVec[(outputCtxLen + innerLen) * nCols + i*nCols + j] == 0);
                 }
 
                 /* Check left context is preserved. */
@@ -134,46 +155,47 @@ TEST_CASE("Postprocessing - erasing required elements")
         }
 
         /* Check inner elements are preserved. */
-        for (size_t i = ctxLen * nCols; i < (ctxLen + innerLen) * nCols; ++i) {
+        for (size_t i = outputCtxLen * nCols; i < (outputCtxLen + innerLen) * nCols; ++i) {
             CHECK(tensorVec[i] == originalVec[i]);
         }
     }
 
     SECTION("Left and right context erase")
     {
-        arm::app::audio::asr::Postprocess post{ctxLen, innerLen, blankTokenIdx};
-
         std::vector <int8_t> tensorVec;
         TfLiteTensor tensor = GetTestTensor<int8_t>(
-                                tensorShape, 100, tensorVec);
+                tensorShape, 100, tensorVec);
+        arm::app::ASRPostProcess post{classifier, &tensor, dummyLabels, dummyResult, outputCtxLen,
+                                      blankTokenIdx, arm::app::Wav2LetterModel::ms_outputRowsIdx};
 
         /* Copy elements to compare later. */
         std::vector <int8_t> originalVec = tensorVec;
 
         /* This step should erase right context. */
-        REQUIRE(true == post.Invoke(&tensor, arm::app::Wav2LetterModel::ms_outputRowsIdx, false));
+        post.m_lastIteration = false;
+        REQUIRE(post.DoPostProcess());
 
         /* Calling it the second time should erase the left context. */
-        REQUIRE(true == post.Invoke(&tensor, arm::app::Wav2LetterModel::ms_outputRowsIdx, false));
+        REQUIRE(post.DoPostProcess());
 
         REQUIRE(originalVec != tensorVec);
 
         /* The first and last ctxLen * 10 elements should be gone. */
-        for (size_t i = 0; i < ctxLen; ++i) {
+        for (size_t i = 0; i < outputCtxLen; ++i) {
             for (size_t j = 0; j < nCols; ++j) {
                 /* Check left and right context elements are zeroed. */
                 if (j == blankTokenIdx) {
-                    CHECK(tensorVec[(ctxLen + innerLen) * nCols + i*nCols + j] == 1);
+                    CHECK(tensorVec[(outputCtxLen + innerLen) * nCols + i*nCols + j] == 1);
                     CHECK(tensorVec[i*nCols + j] == 1);
                 } else {
-                    CHECK(tensorVec[(ctxLen + innerLen) * nCols + i*nCols + j] == 0);
+                    CHECK(tensorVec[(outputCtxLen + innerLen) * nCols + i*nCols + j] == 0);
                     CHECK(tensorVec[i*nCols + j] == 0);
                 }
             }
         }
 
         /* Check inner elements are preserved. */
-        for (size_t i = ctxLen * nCols; i < (ctxLen + innerLen) * nCols; ++i) {
+        for (size_t i = outputCtxLen * nCols; i < (outputCtxLen + innerLen) * nCols; ++i) {
             /* Check left context is preserved. */
             CHECK(tensorVec[i] == originalVec[i]);
         }
@@ -181,18 +203,20 @@ TEST_CASE("Postprocessing - erasing required elements")
 
     SECTION("Try left context erase")
     {
-        /* Should not be able to erase the left context if it is the first iteration. */
-        arm::app::audio::asr::Postprocess post{ctxLen, innerLen, blankTokenIdx};
-
         std::vector <int8_t> tensorVec;
         TfLiteTensor tensor = GetTestTensor<int8_t>(
-                                tensorShape, 100, tensorVec);
+                tensorShape, 100, tensorVec);
+
+        /* Should not be able to erase the left context if it is the first iteration. */
+        arm::app::ASRPostProcess post{classifier, &tensor, dummyLabels, dummyResult, outputCtxLen,
+                                      blankTokenIdx, arm::app::Wav2LetterModel::ms_outputRowsIdx};
 
         /* Copy elements to compare later. */
         std::vector <int8_t> originalVec = tensorVec;
 
         /* Calling it the second time should erase the left context. */
-        REQUIRE(true == post.Invoke(&tensor, arm::app::Wav2LetterModel::ms_outputRowsIdx, true));
+        post.m_lastIteration = true;
+        REQUIRE(post.DoPostProcess());
 
         REQUIRE(originalVec == tensorVec);
     }
diff --git a/tests/use_case/asr/Wav2LetterPreprocessingTest.cc b/tests/use_case/asr/Wav2LetterPreprocessingTest.cc
index 457257f..0280af6 100644
--- a/tests/use_case/asr/Wav2LetterPreprocessingTest.cc
+++ b/tests/use_case/asr/Wav2LetterPreprocessingTest.cc
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021 Arm Limited. All rights reserved.
+ * Copyright (c) 2021-2022 Arm Limited. All rights reserved.
  * SPDX-License-Identifier: Apache-2.0
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
@@ -24,55 +24,46 @@ constexpr uint32_t numMfccVectors  = 10;
 
 /* Test vector output: generated using test-asr-preprocessing.py. */
 int8_t expectedResult[numMfccVectors][numMfccFeatures * 3] = {
-    /* Feature vec 0. */
-    -32,   4,  -9,  -8, -10, -10, -11, -11, -11, -11, -12, -11, -11,    /* MFCCs.   */
-    -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11,    /* Delta 1. */
-    -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10,    /* Delta 2. */
-
-    /* Feature vec 1. */
-    -31,   4,  -9,  -8, -10, -10, -11, -11, -11, -11, -12, -11, -11,
-    -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11,
-    -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10,
-
-    /* Feature vec 2. */
-    -31,   4,  -9,  -9, -10, -10, -11, -11, -11, -11, -12, -12, -12,
-    -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11,
-    -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10,
-
-    /* Feature vec 3. */
-    -31,   4,  -9,  -9, -10, -10, -11, -11, -11, -11, -11, -12, -12,
-    -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11,
-    -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10,
-
-    /* Feature vec 4 : this should have valid delta 1 and delta 2. */
-    -31,   4,  -9,  -9, -10, -10, -11, -11, -11, -11, -11, -12, -12,
-    -38, -29,  -9,   1,  -2,  -7,  -8,  -8, -12, -16, -14,  -5,   5,
-    -68, -50, -13,   5,   0,  -9,  -9,  -8, -13, -20, -19,  -3,  15,
-
-    /* Feature vec 5 : this should have valid delta 1 and delta 2. */
-    -31,   4,  -9,  -8, -10, -10, -11, -11, -11, -11, -11, -12, -12,
-    -62, -45, -11,   5,   0,  -8,  -9,  -8, -12, -19, -17,  -3,  13,
-    -27, -22, -13,  -9, -11, -12, -12, -11, -11, -13, -13, -10,  -6,
-
-    /* Feature vec 6. */
-    -31,   4,  -9,  -8, -10, -10, -11, -11, -11, -11, -12, -11, -11,
-    -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11,
-    -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10,
-
-    /* Feature vec 7. */
-    -32,   4,  -9,  -8, -10, -10, -11, -11, -11, -12, -12, -11, -11,
-    -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11,
-    -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10,
-
-    /* Feature vec 8. */
-    -32,   4,  -9,  -8, -10, -10, -11, -11, -11, -12, -12, -11, -11,
-    -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11,
-    -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10,
-
-    /* Feature vec 9. */
-    -31,   4,  -9,  -8, -10, -10, -11, -11, -11, -11, -12, -11, -11,
-    -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11,
-    -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10
+        /* Feature vec 0. */
+        {-32,   4,  -9,  -8, -10, -10, -11, -11, -11, -11, -12, -11, -11,    /* MFCCs.   */
+        -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11,     /* Delta 1. */
+        -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10},    /* Delta 2. */
+        /* Feature vec 1. */
+        {-31,   4,  -9,  -8, -10, -10, -11, -11, -11, -11, -12, -11, -11,
+        -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11,
+        -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10},
+        /* Feature vec 2. */
+        {-31,   4,  -9,  -9, -10, -10, -11, -11, -11, -11, -12, -12, -12,
+        -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11,
+        -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10},
+        /* Feature vec 3. */
+        {-31,   4,  -9,  -9, -10, -10, -11, -11, -11, -11, -11, -12, -12,
+        -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11,
+        -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10},
+        /* Feature vec 4 : this should have valid delta 1 and delta 2. */
+        {-31,   4,  -9,  -9, -10, -10, -11, -11, -11, -11, -11, -12, -12,
+        -38, -29,  -9,   1,  -2,  -7,  -8,  -8, -12, -16, -14,  -5,   5,
+        -68, -50, -13,   5,   0,  -9,  -9,  -8, -13, -20, -19,  -3,  15},
+        /* Feature vec 5 : this should have valid delta 1 and delta 2. */
+        {-31,   4,  -9,  -8, -10, -10, -11, -11, -11, -11, -11, -12, -12,
+        -62, -45, -11,   5,   0,  -8,  -9,  -8, -12, -19, -17,  -3,  13,
+        -27, -22, -13,  -9, -11, -12, -12, -11, -11, -13, -13, -10,  -6},
+        /* Feature vec 6. */
+        {-31,   4,  -9,  -8, -10, -10, -11, -11, -11, -11, -12, -11, -11,
+        -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11,
+        -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10},
+        /* Feature vec 7. */
+        {-32,   4,  -9,  -8, -10, -10, -11, -11, -11, -12, -12, -11, -11,
+        -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11,
+        -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10},
+        /* Feature vec 8. */
+        {-32,   4,  -9,  -8, -10, -10, -11, -11, -11, -12, -12, -11, -11,
+        -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11,
+        -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10},
+        /* Feature vec 9. */
+        {-31,   4,  -9,  -8, -10, -10, -11, -11, -11, -11, -12, -11, -11,
+        -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11, -11,
+        -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10, -10}
 };
 
 void PopulateTestWavVector(std::vector<int16_t>& vec)
@@ -97,15 +88,16 @@ void PopulateTestWavVector(std::vector<int16_t>& vec)
 TEST_CASE("Preprocessing calculation INT8")
 {
     /* Constants. */
-    const uint32_t  windowLen       = 512;
-    const uint32_t  windowStride    = 160;
-    int             dimArray[]      = {3, 1, numMfccFeatures * 3, numMfccVectors};
-    const float     quantScale      = 0.1410219967365265;
-    const int       quantOffset     = -11;
+    const uint32_t  mfccWindowLen      = 512;
+    const uint32_t  mfccWindowStride   = 160;
+    int             dimArray[]         = {3, 1, numMfccFeatures * 3, numMfccVectors};
+    const float     quantScale         = 0.1410219967365265;
+    const int       quantOffset        = -11;
 
     /* Test wav memory. */
-    std::vector <int16_t> testWav((windowStride * numMfccVectors) +
-                                  (windowLen - windowStride));
+    std::vector<int16_t> testWav((mfccWindowStride * numMfccVectors) +
+                                  (mfccWindowLen - mfccWindowStride)
+                                 );
 
     /* Populate with dummy input. */
     PopulateTestWavVector(testWav);
@@ -115,20 +107,20 @@ TEST_CASE("Preprocessing calculation INT8")
 
     /* Initialise dimensions and the test tensor. */
     TfLiteIntArray* dims= tflite::testing::IntArrayFromInts(dimArray);
-    TfLiteTensor tensor = tflite::testing::CreateQuantizedTensor(
-        tensorVec.data(), dims, quantScale, quantOffset, "preprocessedInput");
+    TfLiteTensor inputTensor = tflite::testing::CreateQuantizedTensor(
+            tensorVec.data(), dims, quantScale, quantOffset, "preprocessedInput");
 
     /* Initialise pre-processing module. */
-    arm::app::audio::asr::Preprocess prep{
-        numMfccFeatures, windowLen, windowStride, numMfccVectors};
+    arm::app::ASRPreProcess prep{&inputTensor,
+        numMfccFeatures, numMfccVectors, mfccWindowLen, mfccWindowStride};
 
     /* Invoke pre-processing. */
-    REQUIRE(prep.Invoke(testWav.data(), testWav.size(), &tensor));
+    REQUIRE(prep.DoPreProcess(testWav.data(), testWav.size()));
 
     /* Wrap the tensor with a std::vector for ease. */
-    auto* tensorData = tflite::GetTensorData<int8_t>(&tensor);
+    auto* tensorData = tflite::GetTensorData<int8_t>(&inputTensor);
     std::vector <int8_t> vecResults =
-        std::vector<int8_t>(tensorData, tensorData + tensor.bytes);
+            std::vector<int8_t>(tensorData, tensorData + inputTensor.bytes);
 
     /* Check sizes. */
     REQUIRE(vecResults.size() == sizeof(expectedResult));