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Diffstat (limited to 'samples/SpeechRecognition/src/MFCC.cpp')
| -rw-r--r-- | samples/SpeechRecognition/src/MFCC.cpp | 397 |
1 files changed, 397 insertions, 0 deletions
diff --git a/samples/SpeechRecognition/src/MFCC.cpp b/samples/SpeechRecognition/src/MFCC.cpp new file mode 100644 index 0000000000..234b14d3be --- /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; +} + |