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