| /* |
| * SPDX-FileCopyrightText: Copyright 2021 Arm Limited and/or its affiliates <open-source-office@arm.com> |
| * 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 MFCC_HPP |
| #define MFCC_HPP |
| |
| #include "PlatformMath.hpp" |
| |
| #include <vector> |
| #include <cstdint> |
| #include <cmath> |
| #include <limits> |
| #include <string> |
| |
| namespace arm { |
| namespace app { |
| namespace audio { |
| |
| /* MFCC's consolidated parameters. */ |
| class MfccParams { |
| public: |
| float m_samplingFreq; |
| uint32_t m_numFbankBins; |
| float m_melLoFreq; |
| float m_melHiFreq; |
| uint32_t m_numMfccFeatures; |
| uint32_t m_frameLen; |
| uint32_t m_frameLenPadded; |
| bool m_useHtkMethod; |
| |
| /** @brief Constructor */ |
| MfccParams(float samplingFreq, uint32_t numFbankBins, |
| float melLoFreq, float melHiFreq, |
| uint32_t numMfccFeats, uint32_t frameLen, |
| bool useHtkMethod); |
| |
| MfccParams() = delete; |
| |
| ~MfccParams() = default; |
| |
| /** @brief Log parameters */ |
| void Log() const; |
| }; |
| |
| /** |
| * @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<float> MfccCompute(const std::vector<int16_t>& 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<typename T> |
| std::vector<T> MfccComputeQuant(const std::vector<int16_t>& 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 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<float>& fftVec, |
| std::vector<std::vector<float>>& melFilterBank, |
| std::vector<uint32_t>& filterBankFilterFirst, |
| std::vector<uint32_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( |
| 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: |
| MfccParams 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<float> m_dctMatrix; |
| std::vector<uint32_t> m_filterBankFilterFirst; |
| std::vector<uint32_t> m_filterBankFilterLast; |
| bool m_filterBankInitialised; |
| arm::app::math::FftInstance m_fftInstance; |
| |
| /** |
| * @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<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<int16_t>& audioData); |
| |
| /** @brief Computes the magnitude from an interleaved complex array. */ |
| void ConvertToPowerSpectrum(); |
| |
| }; |
| |
| } /* namespace audio */ |
| } /* namespace app */ |
| } /* namespace arm */ |
| |
| #endif /* MFCC_HPP */ |