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Diffstat (limited to 'samples/common/src/Audio/MFCC.cpp')
| -rw-r--r-- | samples/common/src/Audio/MFCC.cpp | 354 |
1 files changed, 354 insertions, 0 deletions
diff --git a/samples/common/src/Audio/MFCC.cpp b/samples/common/src/Audio/MFCC.cpp new file mode 100644 index 0000000000..911c32b26e --- /dev/null +++ b/samples/common/src/Audio/MFCC.cpp @@ -0,0 +1,354 @@ +// +// Copyright © 2020 Arm Ltd and Contributors. All rights reserved. +// SPDX-License-Identifier: MIT +// +#include "MFCC.hpp" +#include "MathUtils.hpp" + +#include <cfloat> +#include <cinttypes> +#include <cstring> + +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 auto multiplier = static_cast<float>(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 * cosf(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 / ms_freqStep; + + if (freq >= ms_minLogHz) + { + mel = ms_minLogMel + logf(freq / ms_minLogHz) / ms_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 = ms_freqStep * melFreq; + + if (melFreq >= ms_minLogMel) + { + freq = ms_minLogHz * expf(ms_logStep * (melFreq - ms_minLogMel)); + } + return freq; + } +} + + +bool MFCC::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(); + float melEnergy = FLT_MIN; /* Avoid log of zero at later stages */ + 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++) + { + float energyRep = sqrt(fftVec[i]); + melEnergy += (*filterBankIter++ * energyRep); + } + + melEnergies[bin] = melEnergy; + } + + return true; +} + +void MFCC::ConvertToLogarithmicScale(std::vector<float>& melEnergies) +{ + for (float& melEnergy : melEnergies) + { + melEnergy = logf(melEnergy); + } +} + +void MFCC::ConvertToPowerSpectrum() +{ + const uint32_t halfDim = this->m_buffer.size() / 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> dctMatrix(inputLength * coefficientCount); + + const float normalizer = sqrtf(2.0f/inputLength); + const float angleIncr = M_PI/inputLength; + float angle = 0; + + for (int32_t k = 0, m = 0; k < coefficientCount; k++, m += inputLength) + { + for (int32_t n = 0; n < inputLength; n++) + { + dctMatrix[m + n] = normalizer * cosf((n + 0.5f) * angle); + } + angle += angleIncr; + } + + return dctMatrix; +} + +float MFCC::GetMelFilterBankNormaliser( + const float& leftMel, + const float& rightMel, + const bool useHTKMethod) +{ + /* By default, no normalisation => return 1 */ + return 1.f; +} + +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() const +{ + return this->m_filterBankInitialised; +} + +void MFCC::MfccComputePreFeature(const std::vector<float>& audioData) +{ + this->InitMelFilterBank(); + + auto size = std::min(std::min(this->m_frame.size(), audioData.size()), + static_cast<size_t>(this->m_params.m_frameLen)) * sizeof(float); + std::memcpy(this->m_frame.data(), audioData.data(), size); + + /* 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<uint32_t>(this->m_params.m_numFbankBins); + this->m_filterBankFilterLast = + std::vector<uint32_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; + + uint32_t firstIndex = 0; + uint32_t lastIndex = 0; + bool firstIndexFound = false; + 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 (!firstIndexFound) + { + firstIndex = i; + firstIndexFound = true; + } + lastIndex = i; + } + } + + this->m_filterBankFilterFirst[bin] = firstIndex; + this->m_filterBankFilterLast[bin] = lastIndex; + + /* Copy the part we care about. */ + for (uint32_t i = firstIndex; i <= lastIndex; i++) + { + melFilterBank[bin].push_back(thisBin[i]); + } + } + + return melFilterBank; +} |