forked from Qortal/Brooklyn
235 lines
8.9 KiB
C++
235 lines
8.9 KiB
C++
//
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// Copyright © 2020 Arm Ltd and Contributors. All rights reserved.
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// SPDX-License-Identifier: MIT
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//
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#pragma once
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#include <vector>
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#include <cstdint>
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#include <cmath>
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#include <limits>
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#include <string>
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/* MFCC's consolidated parameters */
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class MfccParams
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{
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public:
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float m_samplingFreq;
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int m_numFbankBins;
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float m_melLoFreq;
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float m_melHiFreq;
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int m_numMfccFeatures;
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int m_frameLen;
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int m_frameLenPadded;
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bool m_useHtkMethod;
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int m_numMfccVectors;
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/** @brief Constructor */
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MfccParams(const float samplingFreq, const int numFbankBins,
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const float melLoFreq, const float melHiFreq,
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const int numMfccFeats, const int frameLen,
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const bool useHtkMethod, const int numMfccVectors);
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/* Delete the default constructor */
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MfccParams() = delete;
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/* Default destructor */
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~MfccParams() = default;
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/** @brief String representation of parameters */
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std::string Str();
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};
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/**
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* @brief Class for MFCC feature extraction.
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* Based on https://github.com/ARM-software/ML-KWS-for-MCU/blob/master/Deployment/Source/MFCC/mfcc.cpp
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* This class is designed to be generic and self-sufficient but
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* certain calculation routines can be overridden to accommodate
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* use-case specific requirements.
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*/
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class MFCC {
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public:
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/**
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* @brief Constructor
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* @param[in] params MFCC parameters
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*/
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explicit MFCC(const MfccParams& params);
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MFCC() = delete;
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~MFCC() = default;
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/**
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* @brief Extract MFCC features for one single small frame of
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* audio data e.g. 640 samples.
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* @param[in] audioData Vector of audio samples to calculate
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* features for.
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* @return Vector of extracted MFCC features.
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**/
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std::vector<float> MfccCompute(const std::vector<float>& audioData);
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/** @brief Initialise. */
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void Init();
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/**
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* @brief Extract MFCC features and quantise for one single small
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* frame of audio data e.g. 640 samples.
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* @param[in] audioData Vector of audio samples to calculate
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* features for.
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* @param[in] quantScale Quantisation scale.
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* @param[in] quantOffset Quantisation offset.
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* @return Vector of extracted quantised MFCC features.
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**/
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template<typename T>
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std::vector<T> MfccComputeQuant(const std::vector<float>& audioData,
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const float quantScale,
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const int quantOffset)
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{
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this->MfccComputePreFeature(audioData);
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float minVal = std::numeric_limits<T>::min();
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float maxVal = std::numeric_limits<T>::max();
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std::vector<T> mfccOut(this->m_params.m_numMfccFeatures);
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const size_t numFbankBins = this->m_params.m_numFbankBins;
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/* Take DCT. Uses matrix mul. */
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for (size_t i = 0, j = 0; i < mfccOut.size(); ++i, j += numFbankBins)
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{
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float sum = 0;
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for (size_t k = 0; k < numFbankBins; ++k)
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{
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sum += this->m_dctMatrix[j + k] * this->m_melEnergies[k];
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}
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/* Quantize to T. */
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sum = std::round((sum / quantScale) + quantOffset);
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mfccOut[i] = static_cast<T>(std::min<float>(std::max<float>(sum, minVal), maxVal));
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}
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return mfccOut;
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}
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MfccParams m_params;
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/* Constants */
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static constexpr float ms_logStep = /*logf(6.4)*/ 1.8562979903656 / 27.0;
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static constexpr float ms_freqStep = 200.0 / 3;
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static constexpr float ms_minLogHz = 1000.0;
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static constexpr float ms_minLogMel = ms_minLogHz / ms_freqStep;
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protected:
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/**
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* @brief Project input frequency to Mel Scale.
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* @param[in] freq Input frequency in floating point.
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* @param[in] useHTKMethod bool to signal if HTK method is to be
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* used for calculation.
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* @return Mel transformed frequency in floating point.
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**/
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static float MelScale(float freq,
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bool useHTKMethod = true);
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/**
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* @brief Inverse Mel transform - convert MEL warped frequency
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* back to normal frequency.
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* @param[in] melFreq Mel frequency in floating point.
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* @param[in] useHTKMethod bool to signal if HTK method is to be
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* used for calculation.
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* @return Real world frequency in floating point.
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**/
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static float InverseMelScale(float melFreq,
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bool useHTKMethod = true);
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/**
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* @brief Populates MEL energies after applying the MEL filter
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* bank weights and adding them up to be placed into
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* bins, according to the filter bank's first and last
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* indices (pre-computed for each filter bank element
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* by CreateMelFilterBank function).
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* @param[in] fftVec Vector populated with FFT magnitudes.
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* @param[in] melFilterBank 2D Vector with filter bank weights.
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* @param[in] filterBankFilterFirst Vector containing the first indices of filter bank
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* to be used for each bin.
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* @param[in] filterBankFilterLast Vector containing the last indices of filter bank
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* to be used for each bin.
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* @param[out] melEnergies Pre-allocated vector of MEL energies to be
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* populated.
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* @return true if successful, false otherwise.
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*/
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virtual bool ApplyMelFilterBank(
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std::vector<float>& fftVec,
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std::vector<std::vector<float>>& melFilterBank,
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std::vector<uint32_t>& filterBankFilterFirst,
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std::vector<uint32_t>& filterBankFilterLast,
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std::vector<float>& melEnergies);
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/**
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* @brief Converts the Mel energies for logarithmic scale.
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* @param[in,out] melEnergies 1D vector of Mel energies.
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**/
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virtual void ConvertToLogarithmicScale(std::vector<float>& melEnergies);
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/**
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* @brief Create a matrix used to calculate Discrete Cosine
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* Transform.
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* @param[in] inputLength Input length of the buffer on which
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* DCT will be performed.
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* @param[in] coefficientCount Total coefficients per input length.
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* @return 1D vector with inputLength x coefficientCount elements
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* populated with DCT coefficients.
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*/
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virtual std::vector<float> CreateDCTMatrix(
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int32_t inputLength,
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int32_t coefficientCount);
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/**
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* @brief Given the low and high Mel values, get the normaliser
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* for weights to be applied when populating the filter
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* bank.
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* @param[in] leftMel Low Mel frequency value.
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* @param[in] rightMel High Mel frequency value.
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* @param[in] useHTKMethod bool to signal if HTK method is to be
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* used for calculation.
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* @return Value to use for normalizing.
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*/
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virtual float GetMelFilterBankNormaliser(
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const float& leftMel,
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const float& rightMel,
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bool useHTKMethod);
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private:
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std::vector<float> m_frame;
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std::vector<float> m_buffer;
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std::vector<float> m_melEnergies;
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std::vector<float> m_windowFunc;
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std::vector<std::vector<float>> m_melFilterBank;
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std::vector<float> m_dctMatrix;
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std::vector<uint32_t> m_filterBankFilterFirst;
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std::vector<uint32_t> m_filterBankFilterLast;
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bool m_filterBankInitialised;
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/**
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* @brief Initialises the filter banks and the DCT matrix. **/
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void InitMelFilterBank();
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/**
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* @brief Signals whether the instance of MFCC has had its
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* required buffers initialised.
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* @return true if initialised, false otherwise.
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**/
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bool IsMelFilterBankInited() const;
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/**
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* @brief Create mel filter banks for MFCC calculation.
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* @return 2D vector of floats.
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**/
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std::vector<std::vector<float>> CreateMelFilterBank();
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/**
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* @brief Computes and populates internal memeber buffers used
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* in MFCC feature calculation
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* @param[in] audioData 1D vector of 16-bit audio data.
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*/
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void MfccComputePreFeature(const std::vector<float>& audioData);
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/** @brief Computes the magnitude from an interleaved complex array. */
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void ConvertToPowerSpectrum();
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};
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