source/application/main/Mfcc.cc - ml/ethos-u/ml-embedded-evaluation-kit - Gitiles

 /*
  * 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 "log_macros.h"

 #include <cfloat>
 #include <cinttypes>

 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)
     {}

     void MfccParams::Log() const
     {
         debug("MFCC parameters:\n");
         debug("\t Sampling frequency:         %f\n", this->m_samplingFreq);
         debug("\t Number of filter banks:     %" PRIu32 "\n", this->m_numFbankBins);
         debug("\t Mel frequency limit (low):  %f\n", this->m_melLoFreq);
         debug("\t Mel frequency limit (high): %f\n", this->m_melHiFreq);
         debug("\t Number of MFCC features:    %" PRIu32 "\n", this->m_numMfccFeatures);
         debug("\t Frame length:               %" PRIu32 "\n", this->m_frameLen);
         debug("\t Padded frame length:        %" PRIu32 "\n", this->m_frameLenPadded);
         debug("\t Using HTK for Mel scale:    %s\n", this->m_useHtkMethod ? "yes" : "no");
     }

     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 *
                 math::MathUtils::CosineF32(static_cast<float>(i) * multiplier)));
         }

         math::MathUtils::FftInitF32(this->m_params.m_frameLenPadded, this->m_fftInstance);
         this->m_params.Log();
     }

     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_err("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 = math::MathUtils::SqrtF32(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];

         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 + 0.5f) * 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() const
     {
         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/(1u<<15u);
         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<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;
     }

 } /* namespace audio */
 } /* namespace app */
 } /* namespace arm */
	/*
	* 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 "log_macros.h"

	#include <cfloat>
	#include <cinttypes>

	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)
	{}

	void MfccParams::Log() const
	{
	debug("MFCC parameters:\n");
	debug("\t Sampling frequency: %f\n", this->m_samplingFreq);
	debug("\t Number of filter banks: %" PRIu32 "\n", this->m_numFbankBins);
	debug("\t Mel frequency limit (low): %f\n", this->m_melLoFreq);
	debug("\t Mel frequency limit (high): %f\n", this->m_melHiFreq);
	debug("\t Number of MFCC features: %" PRIu32 "\n", this->m_numMfccFeatures);
	debug("\t Frame length: %" PRIu32 "\n", this->m_frameLen);
	debug("\t Padded frame length: %" PRIu32 "\n", this->m_frameLenPadded);
	debug("\t Using HTK for Mel scale: %s\n", this->m_useHtkMethod ? "yes" : "no");
	}

	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 *
	math::MathUtils::CosineF32(static_cast<float>(i) * multiplier)));
	}

	math::MathUtils::FftInitF32(this->m_params.m_frameLenPadded, this->m_fftInstance);
	this->m_params.Log();
	}

	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_err("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 = math::MathUtils::SqrtF32(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];

	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 + 0.5f) * 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() const
	{
	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/(1u<<15u);
	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<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;
	}

	} /* namespace audio */
	} /* namespace app */
	} /* namespace arm */