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Diffstat (limited to 'samples/SpeechRecognition/include/MFCC.hpp')
| -rw-r--r-- | samples/SpeechRecognition/include/MFCC.hpp | 244 |
1 files changed, 244 insertions, 0 deletions
diff --git a/samples/SpeechRecognition/include/MFCC.hpp b/samples/SpeechRecognition/include/MFCC.hpp new file mode 100644 index 0000000000..14b6d9fe79 --- /dev/null +++ b/samples/SpeechRecognition/include/MFCC.hpp @@ -0,0 +1,244 @@ +// +// Copyright © 2020 Arm Ltd and Contributors. All rights reserved. +// SPDX-License-Identifier: MIT +// + +#pragma once + +#include <vector> +#include <cstdint> +#include <cmath> +#include <limits> +#include <string> + +/* 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 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<float> MfccCompute(const std::vector<float>& audioData); + + MfccParams _m_params; + + /** + * @brief Constructor + * @param[in] params - MFCC parameters + */ + MFCC(const MfccParams& params); + + /* Delete the default constructor */ + MFCC() = delete; + + /** @brief Default destructor */ + ~MFCC() = default; + + /** @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<typename T> + std::vector<T> MfccComputeQuant(const std::vector<float>& audioData, + const float quantScale, + const int quantOffset) + { + this->_MfccComputePreFeature(audioData); + float minVal = std::numeric_limits<T>::min(); + float maxVal = std::numeric_limits<T>::max(); + + std::vector<T> 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<T>(std::min<float>(std::max<float>(sum, minVal), maxVal)); + } + + return mfccOut; + } + + /* Constants */ + static constexpr float logStep = 1.8562979903656 / 27.0; + static constexpr float freqStep = 200.0 / 3; + static constexpr float minLogHz = 1000.0; + static constexpr float minLogMel = minLogHz / 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(const float freq, + const bool useHTKMethod = true); + + /** + * @brief Inverse Mel transform - convert MEL warped frequency + * back to normal frequency + * @param[in] freq - 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(const float melFreq, + const 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<float>& fftVec, + std::vector<std::vector<float>>& melFilterBank, + std::vector<int32_t>& filterBankFilterFirst, + std::vector<int32_t>& filterBankFilterLast, + std::vector<float>& melEnergies); + + /** + * @brief Converts the Mel energies for logarithmic scale + * @param[in/out] melEnergies - 1D vector of Mel energies + **/ + virtual void ConvertToLogarithmicScale(std::vector<float>& 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<float> CreateDCTMatrix( + const int32_t inputLength, + const 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 + */ + virtual float GetMelFilterBankNormaliser( + const float& leftMel, + const float& rightMel, + const bool useHTKMethod); + +private: + + std::vector<float> _m_frame; + std::vector<float> _m_buffer; + std::vector<float> _m_melEnergies; + std::vector<float> _m_windowFunc; + std::vector<std::vector<float>> _m_melFilterBank; + std::vector<float> _m_dctMatrix; + std::vector<int32_t> _m_filterBankFilterFirst; + std::vector<int32_t> _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(); + + /** + * @brief Create mel filter banks for MFCC calculation. + * @return 2D vector of floats + **/ + std::vector<std::vector<float>> _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<float>& audioData); + + /** @brief Computes the magnitude from an interleaved complex array */ + void _ConvertToPowerSpectrum(); + +}; + |