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Diffstat (limited to 'source/application/main/Mfcc.cc')
| -rw-r--r-- | source/application/main/Mfcc.cc | 354 |
1 files changed, 354 insertions, 0 deletions
diff --git a/source/application/main/Mfcc.cc b/source/application/main/Mfcc.cc new file mode 100644 index 0000000..bf16159 --- /dev/null +++ b/source/application/main/Mfcc.cc @@ -0,0 +1,354 @@ +/* + * Copyright (c) 2021 Arm Limited. All rights reserved. + * SPDX-License-Identifier: Apache-2.0 + * + * Licensed under the Apache License, Version 2.0 (the "License"); + * you may not use this file except in compliance with the License. + * You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ +#include "Mfcc.hpp" + +#include "PlatformMath.hpp" + +#include <cfloat> + +namespace arm { +namespace app { +namespace audio { + + MfccParams::MfccParams( + const float samplingFreq, + const uint32_t numFbankBins, + const float melLoFreq, + const float melHiFreq, + const uint32_t numMfccFeats, + const uint32_t frameLen, + const bool useHtkMethod): + m_samplingFreq(samplingFreq), + m_numFbankBins(numFbankBins), + m_melLoFreq(melLoFreq), + m_melHiFreq(melHiFreq), + m_numMfccFeatures(numMfccFeats), + m_frameLen(frameLen), + + /* 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 * + math::MathUtils::CosineF32(static_cast<float>(i) * multiplier))); + } + + math::MathUtils::FftInitF32(this->_m_params.m_frameLenPadded, this->_m_fftInstance); + debug("Instantiated MFCC object: %s\n", this->_m_params.Str().c_str()); + } + + 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<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_err("unexpected filter bank lengths\n"); + return false; + } + + for (size_t bin = 0; bin < numBanks; ++bin) { + auto filterBankIter = melFilterBank[bin].begin(); + float melEnergy = FLT_MIN; /* Avoid log of zero at later stages */ + int32_t firstIndex = filterBankFilterFirst[bin]; + int32_t lastIndex = filterBankFilterLast[bin]; + + for (int i = firstIndex; i <= lastIndex; i++) { + float energyRep = math::MathUtils::SqrtF32(fftVec[i]); + melEnergy += (*filterBankIter++ * energyRep); + } + + melEnergies[bin] = melEnergy; + } + + return true; + } + + void MFCC::ConvertToLogarithmicScale(std::vector<float>& melEnergies) + { + for (size_t bin = 0; bin < melEnergies.size(); ++bin) { + melEnergies[bin] = logf(melEnergies[bin]); + } + } + + 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]; + + math::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); + + const float normalizer = math::MathUtils::SqrtF32(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++) { + dctMatix[m+n] = normalizer * + math::MathUtils::CosineF32((n + 0.5) * angle); + } + angle += angleIncr; + } + + return dctMatix; + } + + float MFCC::GetMelFilterBankNormaliser( + const float& leftMel, + const float& rightMel, + const bool useHTKMethod) + { + UNUSED(leftMel); + UNUSED(rightMel); + UNUSED(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() + { + return this->_m_filterBankInitialised; + } + + void MFCC::_MfccComputePreFeature(const std::vector<int16_t>& audioData) + { + this->_InitMelFilterBank(); + + /* TensorFlow way of normalizing .wav data to (-1, 1). */ + constexpr float normaliser = 1.0/(1<<15); + 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. */ + math::MathUtils::FftF32(this->_m_frame, this->_m_buffer, this->_m_fftInstance); + + /* 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_err("Failed to apply MEL filter banks\n"); + } + + /* Convert to logarithmic scale. */ + this->ConvertToLogarithmicScale(this->_m_melEnergies); + } + + std::vector<float> MFCC::MfccCompute(const std::vector<int16_t>& 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++ = math::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; + } + +} /* namespace audio */ +} /* namespace app */ +} /* namespace arm */ |