1 files changed, 126 insertions, 0 deletions
diff --git a/samples/SpeechRecognition/src/Wav2LetterMFCC.cpp b/samples/SpeechRecognition/src/Wav2LetterMFCC.cpp
new file mode 100644
index 0000000000..959bd9022e
--- /dev/null
+++ b/samples/SpeechRecognition/src/Wav2LetterMFCC.cpp
@@ -0,0 +1,126 @@
+//
+// Copyright © 2020 Arm Ltd and Contributors. All rights reserved.
+// SPDX-License-Identifier: MIT
+//
+#include "Wav2LetterMFCC.hpp"
+#include "MathUtils.hpp"
+
+#include <cfloat>
+
+bool Wav2LetterMFCC::ApplyMelFilterBank(
+        std::vector<float>&                 fftVec,
+        std::vector<std::vector<float>>&    melFilterBank,
+        std::vector<uint32_t>&               filterBankFilterFirst,
+        std::vector<uint32_t>&               filterBankFilterLast,
+        std::vector<float>&                 melEnergies)
+{
+    const size_t numBanks = melEnergies.size();
+
+    if (numBanks != filterBankFilterFirst.size() ||
+            numBanks != filterBankFilterLast.size()) 
+    {
+        printf("Unexpected filter bank lengths\n");
+        return false;
+    }
+
+    for (size_t bin = 0; bin < numBanks; ++bin) 
+    {
+        auto filterBankIter = melFilterBank[bin].begin();
+        auto end = melFilterBank[bin].end();
+        // Avoid log of zero at later stages, same value used in librosa.
+        // The number was used during our default wav2letter model training. 
+        float melEnergy = 1e-10;
+        const uint32_t firstIndex = filterBankFilterFirst[bin];
+        const uint32_t lastIndex = std::min<uint32_t>(filterBankFilterLast[bin], fftVec.size() - 1);
+
+        for (uint32_t i = firstIndex; i <= lastIndex && filterBankIter != end; ++i) 
+        {
+            melEnergy += (*filterBankIter++ * fftVec[i]);
+        }
+
+        melEnergies[bin] = melEnergy;
+    }
+
+    return true;
+}
+
+void Wav2LetterMFCC::ConvertToLogarithmicScale(std::vector<float>& melEnergies)
+{
+    float maxMelEnergy = -FLT_MAX;
+
+    // Container for natural logarithms of mel energies. 
+    std::vector <float> vecLogEnergies(melEnergies.size(), 0.f);
+
+    // Because we are taking natural logs, we need to multiply by log10(e).
+    // Also, for wav2letter model, we scale our log10 values by 10. 
+    constexpr float multiplier = 10.0 *  // Default scalar. 
+                                  0.4342944819032518;  // log10f(std::exp(1.0)) 
+
+    // Take log of the whole vector. 
+    MathUtils::VecLogarithmF32(melEnergies, vecLogEnergies);
+
+    // Scale the log values and get the max. 
+    for (auto iterM = melEnergies.begin(), iterL = vecLogEnergies.begin();
+              iterM != melEnergies.end() && iterL != vecLogEnergies.end(); ++iterM, ++iterL) 
+    {
+
+        *iterM = *iterL * multiplier;
+
+        // Save the max mel energy. 
+        if (*iterM > maxMelEnergy) 
+        {
+            maxMelEnergy = *iterM;
+        }
+    }
+
+    // Clamp the mel energies. 
+    constexpr float maxDb = 80.0;
+    const float clampLevelLowdB = maxMelEnergy - maxDb;
+    for (float& melEnergy : melEnergies) 
+    {
+        melEnergy = std::max(melEnergy, clampLevelLowdB);
+    }
+}
+
+std::vector<float> Wav2LetterMFCC::CreateDCTMatrix(
+                                    const int32_t inputLength,
+                                    const int32_t coefficientCount)
+{
+    std::vector<float> dctMatix(inputLength * coefficientCount);
+
+    // Orthonormal normalization. 
+    const float normalizerK0 = 2 * sqrtf(1.0f /
+                                    static_cast<float>(4 * inputLength));
+    const float normalizer = 2 * sqrtf(1.0f /
+                                    static_cast<float>(2 * inputLength));
+
+    const float angleIncr = M_PI / inputLength;
+    float angle = angleIncr;  // We start using it at k = 1 loop. 
+
+    // First row of DCT will use normalizer K0. 
+    for (int32_t n = 0; n < inputLength; ++n) 
+    {
+        dctMatix[n] = normalizerK0;  // cos(0) = 1 
+    }
+
+    // Second row (index = 1) onwards, we use standard normalizer. 
+    for (int32_t k = 1, m = inputLength; k < coefficientCount; ++k, m += inputLength) 
+    {
+        for (int32_t n = 0; n < inputLength; ++n) 
+        {
+            dctMatix[m+n] = normalizer * cosf((n + 0.5f) * angle);
+        }
+        angle += angleIncr;
+    }
+    return dctMatix;
+}
+
+float Wav2LetterMFCC::GetMelFilterBankNormaliser(
+                                const float&    leftMel,
+                                const float&    rightMel,
+                                const bool      useHTKMethod)
+{
+    // Slaney normalization for mel weights. 
+    return (2.0f / (MFCC::InverseMelScale(rightMel, useHTKMethod) -
+            MFCC::InverseMelScale(leftMel, useHTKMethod)));
+}