| // |
| // 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; |
| } |
| |