Opensource ML embedded evaluation kit
Change-Id: I12e807f19f5cacad7cef82572b6dd48252fd61fd
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 */