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+/*
+ * Copyright (c) 2021 Arm Limited. All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#ifndef ASR_WAV2LETTER_PREPROCESS_HPP
+#define ASR_WAV2LETTER_PREPROCESS_HPP
+
+#include "Wav2LetterModel.hpp"
+#include "Wav2LetterMfcc.hpp"
+#include "AudioUtils.hpp"
+#include "DataStructures.hpp"
+
+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>;
+
+ class Preprocess {
+ 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.
+ */
+ Preprocess(
+ uint32_t numMfccFeatures,
+ uint32_t windowLen,
+ uint32_t windowStride,
+ uint32_t numMfccVectors);
+ Preprocess() = delete;
+ ~Preprocess() = default;
+
+ /**
+ * @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
+ * 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);
+
+ protected:
+ /**
+ * @brief Computes the first and second order deltas for the
+ * MFCC buffers - they are assumed to be populated.
+ *
+ * @param[in] mfcc MFCC buffers.
+ * @param[out] delta1 Result of the first diff computation.
+ * @param[out] delta2 Result of the second diff computation.
+ * @return true if successful, false otherwise.
+ */
+ static bool _ComputeDeltas(Array2d<float>& mfcc,
+ Array2d<float>& delta1,
+ 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,
+ float mean);
+
+ /**
+ * @brief Given a 2D vector of floats, normalises it using
+ * the mean and the stddev.
+ * @param[in,out] vec Vector of vector of floats.
+ */
+ static void _NormaliseVec(Array2d<float>& vec);
+
+ /**
+ * @brief Normalises the MFCC and delta buffers.
+ */
+ void _Normalise();
+
+ /**
+ * @brief Given the quantisation and data type limits, computes
+ * the quantised values of a floating point input data.
+ * @param[in] elem Element to be quantised.
+ * @param[in] quantScale Scale.
+ * @param[in] quantOffset Offset.
+ * @param[in] minVal Numerical limit - minimum.
+ * @param[in] maxVal Numerical limit - maximum.
+ * @return Floating point quantised value.
+ */
+ static float _GetQuantElem(
+ float elem,
+ float quantScale,
+ int quantOffset,
+ float minVal,
+ float maxVal);
+
+ /**
+ * @brief Quantises the MFCC and delta buffers, and places them
+ * in the output buffer. While doing so, it transposes
+ * the data. Reason: Buffers in this class are arranged
+ * for "time" axis to be row major. Primary reason for
+ * this being the convolution speed up (as we can use
+ * contiguous memory). The output, however, requires the
+ * time axis to be in column major arrangement.
+ * @param[in] outputBuf Pointer to the output buffer.
+ * @param[in] outputBufSz Output buffer's size.
+ * @param[in] quantScale Quantisation scale.
+ * @param[in] quantOffset Quantisation offset.
+ */
+ template <typename T>
+ bool _Quantise(
+ T * outputBuf,
+ const uint32_t outputBufSz,
+ const float quantScale,
+ const int quantOffset)
+ {
+ /* Check the output size will fit everything. */
+ if (outputBufSz < (this->_m_mfccBuf.size(0) * 3 * sizeof(T))) {
+ printf_err("Tensor size too small for features\n");
+ return false;
+ }
+
+ /* Populate. */
+ T * outputBufMfcc = outputBuf;
+ T * outputBufD1 = outputBuf + this->_m_numMfccFeats;
+ T * outputBufD2 = outputBufD1 + this->_m_numMfccFeats;
+ const uint32_t ptrIncr = this->_m_numMfccFeats * 2; /* (3 vectors - 1 vector) */
+
+ const float minVal = std::numeric_limits<T>::min();
+ 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 i = 0; i < this->_m_numMfccFeats; ++i) {
+ *outputBufMfcc++ = static_cast<T>(Preprocess::_GetQuantElem(
+ this->_m_mfccBuf(i, j), quantScale,
+ quantOffset, minVal, maxVal));
+ *outputBufD1++ = static_cast<T>(Preprocess::_GetQuantElem(
+ this->_m_delta1Buf(i, j), quantScale,
+ quantOffset, minVal, maxVal));
+ *outputBufD2++ = static_cast<T>(Preprocess::_GetQuantElem(
+ this->_m_delta2Buf(i, j), quantScale,
+ quantOffset, minVal, maxVal));
+ }
+ outputBufMfcc += ptrIncr;
+ outputBufD1 += ptrIncr;
+ outputBufD2 += ptrIncr;
+ }
+
+ return true;
+ }
+
+ private:
+ Wav2LetterMFCC _m_mfcc; /* MFCC instance. */
+
+ /* 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 */
+
+ 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. */
+
+ };
+
+} /* namespace asr */
+} /* namespace audio */
+} /* namespace app */
+} /* namespace arm */
+
+#endif /* ASR_WAV2LETTER_PREPROCESS_HPP */ \ No newline at end of file
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