MLECO-2079 Adding the C++ KWS example
Signed-off-by: Eanna O Cathain <eanna.ocathain@arm.com>
Change-Id: I81899bbfaada32f478c2e2fc6441eabb94d8d0fc
diff --git a/samples/SpeechRecognition/src/Wav2LetterMFCC.cpp b/samples/SpeechRecognition/src/Wav2LetterMFCC.cpp
new file mode 100644
index 0000000..959bd90
--- /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)));
+}