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Diffstat (limited to 'source/use_case/ad/include/MelSpectrogram.hpp')
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diff --git a/source/use_case/ad/include/MelSpectrogram.hpp b/source/use_case/ad/include/MelSpectrogram.hpp new file mode 100644 index 0000000..c1dd61e --- /dev/null +++ b/source/use_case/ad/include/MelSpectrogram.hpp @@ -0,0 +1,233 @@ +/* + * 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. + */ +#ifndef MELSPECTROGRAM_HPP +#define MELSPECTROGRAM_HPP + +#include "PlatformMath.hpp" + +#include <vector> +#include <cstdint> +#include <cmath> +#include <limits> +#include <string> + +namespace arm { +namespace app { +namespace audio { + + /* Mel Spectrogram consolidated parameters */ + class MelSpecParams { + public: + float m_samplingFreq; + uint32_t m_numFbankBins; + float m_melLoFreq; + float m_melHiFreq; + uint32_t m_frameLen; + uint32_t m_frameLenPadded; + bool m_useHtkMethod; + + /** @brief Constructor */ + MelSpecParams(const float samplingFreq, const uint32_t numFbankBins, + const float melLoFreq, const float melHiFreq, + const uint32_t frameLen, const bool useHtkMethod); + + MelSpecParams() = delete; + ~MelSpecParams() = default; + + /** @brief String representation of parameters */ + std::string Str(); + }; + + /** + * @brief Class for Mel Spectrogram 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 MelSpectrogram { + + public: + /** + * @brief Extract Mel Spectrogram 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] trainingMean - Value to subtract from the the computed mel spectrogram, default 0. + * @return Vector of extracted Mel Spectrogram features. + **/ + std::vector<float> ComputeMelSpec(const std::vector<int16_t>& audioData, float trainingMean = 0); + + /** + * @brief Constructor + * @param[in] params - Mel Spectrogram parameters + */ + MelSpectrogram(const MelSpecParams& params); + + MelSpectrogram() = delete; + ~MelSpectrogram() = default; + + /** @brief Initialise */ + void Init(); + + /** + * @brief Extract Mel Spectrogram 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 Mel Spectrogram features. + **/ + template<typename T> + std::vector<T> MelSpecComputeQuant(const std::vector<int16_t>& audioData, + const float quantScale, + const int quantOffset, + float trainingMean = 0) + { + this->ComputeMelSpec(audioData, trainingMean); + float minVal = std::numeric_limits<T>::min(); + float maxVal = std::numeric_limits<T>::max(); + + std::vector<T> melSpecOut(this->_m_params.m_numFbankBins); + const size_t numFbankBins = this->_m_params.m_numFbankBins; + + /* Quantize to T. */ + for (size_t k = 0; k < numFbankBins; ++k) { + auto quantizedEnergy = std::round(((this->_m_melEnergies[k]) / quantScale) + quantOffset); + melSpecOut[k] = static_cast<T>(std::min<float>(std::max<float>(quantizedEnergy, minVal), maxVal)); + } + + return melSpecOut; + } + + /* 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(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 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 Return float value to be applied + * when populating the filter bank. + */ + virtual float GetMelFilterBankNormaliser( + const float& leftMel, + const float& rightMel, + const bool useHTKMethod); + + private: + MelSpecParams _m_params; + 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<int32_t> _m_filterBankFilterFirst; + std::vector<int32_t> _m_filterBankFilterLast; + bool _m_filterBankInitialised; + arm::app::math::FftInstance _m_fftInstance; + + /** + * @brief Initialises the filter banks. + **/ + void _InitMelFilterBank(); + + /** + * @brief Signals whether the instance of MelSpectrogram has had its + * required buffers initialised + * @return True if initialised, false otherwise + **/ + bool _IsMelFilterBankInited(); + + /** + * @brief Create mel filter banks for Mel Spectrogram calculation. + * @return 2D vector of floats + **/ + std::vector<std::vector<float>> _CreateMelFilterBank(); + + /** + * @brief Computes the magnitude from an interleaved complex array + **/ + void _ConvertToPowerSpectrum(); + + }; + +} /* namespace audio */ +} /* namespace app */ +} /* namespace arm */ + + +#endif /* MELSPECTROGRAM_HPP */ |