MLECO-1252 ASR sample application using the public ArmNN C++ API.
Change-Id: I98cd505b8772a8c8fa88308121bc94135bb45068
Signed-off-by: Éanna Ó Catháin <eanna.ocathain@arm.com>
diff --git a/samples/SpeechRecognition/src/MFCC.cpp b/samples/SpeechRecognition/src/MFCC.cpp
new file mode 100644
index 0000000..234b14d
--- /dev/null
+++ b/samples/SpeechRecognition/src/MFCC.cpp
@@ -0,0 +1,397 @@
+//
+// Copyright © 2020 Arm Ltd and Contributors. All rights reserved.
+// SPDX-License-Identifier: MIT
+//
+
+#include <cstdio>
+#include <float.h>
+
+#include "MFCC.hpp"
+#include "MathUtils.hpp"
+
+
+MfccParams::MfccParams(
+ const float samplingFreq,
+ const int numFbankBins,
+ const float melLoFreq,
+ const float melHiFreq,
+ const int numMfccFeats,
+ const int frameLen,
+ const bool useHtkMethod,
+ const int numMfccVectors):
+ m_samplingFreq(samplingFreq),
+ m_numFbankBins(numFbankBins),
+ m_melLoFreq(melLoFreq),
+ m_melHiFreq(melHiFreq),
+ m_numMfccFeatures(numMfccFeats),
+ m_frameLen(frameLen),
+ m_numMfccVectors(numMfccVectors),
+
+ /* Smallest power of 2 >= frame length. */
+ m_frameLenPadded(pow(2, ceil((log(frameLen)/log(2))))),
+ m_useHtkMethod(useHtkMethod)
+{}
+
+std::string MfccParams::Str()
+{
+ char strC[1024];
+ snprintf(strC, sizeof(strC) - 1, "\n \
+ \n\t Sampling frequency: %f\
+ \n\t Number of filter banks: %u\
+ \n\t Mel frequency limit (low): %f\
+ \n\t Mel frequency limit (high): %f\
+ \n\t Number of MFCC features: %u\
+ \n\t Frame length: %u\
+ \n\t Padded frame length: %u\
+ \n\t Using HTK for Mel scale: %s\n",
+ this->m_samplingFreq, this->m_numFbankBins, this->m_melLoFreq,
+ this->m_melHiFreq, this->m_numMfccFeatures, this->m_frameLen,
+ this->m_frameLenPadded, this->m_useHtkMethod ? "yes" : "no");
+ return std::string{strC};
+}
+
+MFCC::MFCC(const MfccParams& params):
+ _m_params(params),
+ _m_filterBankInitialised(false)
+{
+ this->_m_buffer = std::vector<float>(
+ this->_m_params.m_frameLenPadded, 0.0);
+ this->_m_frame = std::vector<float>(
+ this->_m_params.m_frameLenPadded, 0.0);
+ this->_m_melEnergies = std::vector<float>(
+ this->_m_params.m_numFbankBins, 0.0);
+
+ this->_m_windowFunc = std::vector<float>(this->_m_params.m_frameLen);
+ const float multiplier = 2 * M_PI / this->_m_params.m_frameLen;
+
+ /* Create window function. */
+ for (size_t i = 0; i < this->_m_params.m_frameLen; i++)
+ {
+ this->_m_windowFunc[i] = (0.5 - (0.5 * cos(static_cast<float>(i) * multiplier)));
+ }
+}
+
+void MFCC::Init()
+{
+ this->_InitMelFilterBank();
+}
+
+float MFCC::MelScale(const float freq, const bool useHTKMethod)
+{
+ if (useHTKMethod)
+ {
+ return 1127.0f * logf (1.0f + freq / 700.0f);
+ }
+ else
+ {
+ /* Slaney formula for mel scale. */
+ float mel = freq / freqStep;
+
+ if (freq >= minLogHz)
+ {
+ mel = minLogMel + logf(freq / minLogHz) / logStep;
+ }
+ return mel;
+ }
+}
+
+float MFCC::InverseMelScale(const float melFreq, const bool useHTKMethod)
+{
+ if (useHTKMethod)
+ {
+ return 700.0f * (expf (melFreq / 1127.0f) - 1.0f);
+ }
+ else
+ {
+ /* Slaney formula for mel scale. */
+ float freq = freqStep * melFreq;
+
+ if (melFreq >= minLogMel)
+ {
+ freq = minLogHz * expf(logStep * (melFreq - minLogMel));
+ }
+ return freq;
+ }
+}
+
+
+bool MFCC::ApplyMelFilterBank(
+ std::vector<float>& fftVec,
+ std::vector<std::vector<float>>& melFilterBank,
+ std::vector<int32_t>& filterBankFilterFirst,
+ std::vector<int32_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();
+ float melEnergy = 1e-10; /* Avoid log of zero at later stages */
+ const int32_t firstIndex = filterBankFilterFirst[bin];
+ const int32_t lastIndex = filterBankFilterLast[bin];
+
+ for (int32_t i = firstIndex; i <= lastIndex; ++i)
+ {
+ melEnergy += (*filterBankIter++ * fftVec[i]);
+ }
+
+ melEnergies[bin] = melEnergy;
+ }
+
+ return true;
+}
+
+void MFCC::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(); ++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 (auto iter = melEnergies.begin(); iter != melEnergies.end(); ++iter)
+ {
+ *iter = std::max(*iter, clampLevelLowdB);
+ }
+}
+
+void MFCC::_ConvertToPowerSpectrum()
+{
+ const uint32_t halfDim = this->_m_params.m_frameLenPadded / 2;
+
+ /* Handle this special case. */
+ float firstEnergy = this->_m_buffer[0] * this->_m_buffer[0];
+ float lastEnergy = this->_m_buffer[1] * this->_m_buffer[1];
+
+ MathUtils::ComplexMagnitudeSquaredF32(
+ this->_m_buffer.data(),
+ this->_m_buffer.size(),
+ this->_m_buffer.data(),
+ this->_m_buffer.size()/2);
+
+ this->_m_buffer[0] = firstEnergy;
+ this->_m_buffer[halfDim] = lastEnergy;
+}
+
+std::vector<float> MFCC::CreateDCTMatrix(
+ const int32_t inputLength,
+ const int32_t coefficientCount)
+{
+ std::vector<float> dctMatix(inputLength * coefficientCount);
+
+ /* Orthonormal normalization. */
+ const float normalizerK0 = 2 * sqrt(1.0 / static_cast<float>(4*inputLength));
+ const float normalizer = 2 * sqrt(1.0 / 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;
+ }
+
+ /* 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 *
+ cos((n + 0.5) * angle);
+ }
+ angle += angleIncr;
+ }
+ return dctMatix;
+}
+
+float MFCC::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)));
+}
+
+void MFCC::_InitMelFilterBank()
+{
+ if (!this->_IsMelFilterBankInited())
+ {
+ this->_m_melFilterBank = this->_CreateMelFilterBank();
+ this->_m_dctMatrix = this->CreateDCTMatrix(
+ this->_m_params.m_numFbankBins,
+ this->_m_params.m_numMfccFeatures);
+ this->_m_filterBankInitialised = true;
+ }
+}
+
+bool MFCC::_IsMelFilterBankInited()
+{
+ return this->_m_filterBankInitialised;
+}
+
+void MFCC::_MfccComputePreFeature(const std::vector<float>& audioData)
+{
+ this->_InitMelFilterBank();
+
+ /* TensorFlow way of normalizing .wav data to (-1, 1). */
+ constexpr float normaliser = 1.0;
+ for (size_t i = 0; i < this->_m_params.m_frameLen; i++)
+ {
+ this->_m_frame[i] = static_cast<float>(audioData[i]) * normaliser;
+ }
+
+ /* Apply window function to input frame. */
+ for(size_t i = 0; i < this->_m_params.m_frameLen; i++)
+ {
+ this->_m_frame[i] *= this->_m_windowFunc[i];
+ }
+
+ /* Set remaining frame values to 0. */
+ std::fill(this->_m_frame.begin() + this->_m_params.m_frameLen,this->_m_frame.end(), 0);
+
+ /* Compute FFT. */
+ MathUtils::FftF32(this->_m_frame, this->_m_buffer);
+
+ /* Convert to power spectrum. */
+ this->_ConvertToPowerSpectrum();
+
+ /* Apply mel filterbanks. */
+ if (!this->ApplyMelFilterBank(this->_m_buffer,
+ this->_m_melFilterBank,
+ this->_m_filterBankFilterFirst,
+ this->_m_filterBankFilterLast,
+ this->_m_melEnergies))
+ {
+ printf("Failed to apply MEL filter banks\n");
+ }
+
+ /* Convert to logarithmic scale */
+ this->ConvertToLogarithmicScale(this->_m_melEnergies);
+}
+
+std::vector<float> MFCC::MfccCompute(const std::vector<float>& audioData)
+{
+ this->_MfccComputePreFeature(audioData);
+
+ std::vector<float> mfccOut(this->_m_params.m_numMfccFeatures);
+
+ float * ptrMel = this->_m_melEnergies.data();
+ float * ptrDct = this->_m_dctMatrix.data();
+ float * ptrMfcc = mfccOut.data();
+
+ /* Take DCT. Uses matrix mul. */
+ for (size_t i = 0, j = 0; i < mfccOut.size();
+ ++i, j += this->_m_params.m_numFbankBins)
+ {
+ *ptrMfcc++ = MathUtils::DotProductF32(
+ ptrDct + j,
+ ptrMel,
+ this->_m_params.m_numFbankBins);
+ }
+
+ return mfccOut;
+}
+
+std::vector<std::vector<float>> MFCC::_CreateMelFilterBank()
+{
+ size_t numFftBins = this->_m_params.m_frameLenPadded / 2;
+ float fftBinWidth = static_cast<float>(this->_m_params.m_samplingFreq) / this->_m_params.m_frameLenPadded;
+
+ float melLowFreq = MFCC::MelScale(this->_m_params.m_melLoFreq,
+ this->_m_params.m_useHtkMethod);
+ float melHighFreq = MFCC::MelScale(this->_m_params.m_melHiFreq,
+ this->_m_params.m_useHtkMethod);
+ float melFreqDelta = (melHighFreq - melLowFreq) / (this->_m_params.m_numFbankBins + 1);
+
+ std::vector<float> thisBin = std::vector<float>(numFftBins);
+ std::vector<std::vector<float>> melFilterBank(
+ this->_m_params.m_numFbankBins);
+ this->_m_filterBankFilterFirst =
+ std::vector<int32_t>(this->_m_params.m_numFbankBins);
+ this->_m_filterBankFilterLast =
+ std::vector<int32_t>(this->_m_params.m_numFbankBins);
+
+ for (size_t bin = 0; bin < this->_m_params.m_numFbankBins; bin++)
+ {
+ float leftMel = melLowFreq + bin * melFreqDelta;
+ float centerMel = melLowFreq + (bin + 1) * melFreqDelta;
+ float rightMel = melLowFreq + (bin + 2) * melFreqDelta;
+
+ int32_t firstIndex = -1;
+ int32_t lastIndex = -1;
+ const float normaliser = this->GetMelFilterBankNormaliser(leftMel, rightMel, this->_m_params.m_useHtkMethod);
+
+ for (size_t i = 0; i < numFftBins; i++)
+ {
+ float freq = (fftBinWidth * i); /* Center freq of this fft bin. */
+ float mel = MFCC::MelScale(freq, this->_m_params.m_useHtkMethod);
+ thisBin[i] = 0.0;
+
+ if (mel > leftMel && mel < rightMel)
+ {
+ float weight;
+ if (mel <= centerMel)
+ {
+ weight = (mel - leftMel) / (centerMel - leftMel);
+ }
+ else
+ {
+ weight = (rightMel - mel) / (rightMel - centerMel);
+ }
+
+ thisBin[i] = weight * normaliser;
+ if (firstIndex == -1)
+ {
+ firstIndex = i;
+ }
+ lastIndex = i;
+ }
+ }
+
+ this->_m_filterBankFilterFirst[bin] = firstIndex;
+ this->_m_filterBankFilterLast[bin] = lastIndex;
+
+ /* Copy the part we care about. */
+ for (int32_t i = firstIndex; i <= lastIndex; i++)
+ {
+ melFilterBank[bin].push_back(thisBin[i]);
+ }
+ }
+
+ return melFilterBank;
+}
+