samples/SpeechRecognition/include/MFCC.hpp - ml/armnn - Gitiles

 //
 // 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();

 };
	//
	// 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();

	};