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* SPDX-FileCopyrightText: Copyright 2021 Arm Limited and/or its affiliates <>
* 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
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include "Mfcc.hpp"
namespace arm {
namespace app {
namespace audio {
/* Class to provide Wav2Letter specific MFCC calculation requirements. */
class Wav2LetterMFCC : public MFCC {
static constexpr uint32_t ms_defaultSamplingFreq = 16000;
static constexpr uint32_t ms_defaultNumFbankBins = 128;
static constexpr uint32_t ms_defaultMelLoFreq = 0;
static constexpr uint32_t ms_defaultMelHiFreq = 8000;
static constexpr bool ms_defaultUseHtkMethod = false;
explicit Wav2LetterMFCC(const size_t numFeats, const size_t frameLen)
: MFCC(MfccParams(
ms_defaultSamplingFreq, ms_defaultNumFbankBins,
ms_defaultMelLoFreq, ms_defaultMelHiFreq,
numFeats, frameLen, ms_defaultUseHtkMethod))
Wav2LetterMFCC() = delete;
~Wav2LetterMFCC() = default;
* @brief Overrides base class implementation of this 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
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) override;
* @brief Override for the base class implementation convert mel
* energies to logarithmic scale. The difference from
* default behaviour is that the power is converted to dB
* and subsequently clamped.
* @param[in,out] melEnergies 1D vector of Mel energies
void ConvertToLogarithmicScale(std::vector<float>& melEnergies) override;
* @brief Create a matrix used to calculate Discrete Cosine
* Transform. Override for the base class' default
* implementation as the first and last elements
* use a different normaliser.
* @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.
std::vector<float> CreateDCTMatrix(int32_t inputLength,
int32_t coefficientCount) override;
* @brief Given the low and high Mel values, get the normaliser
* for weights to be applied when populating the filter
* bank. Override for the base class implementation.
* @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 normalising.
float GetMelFilterBankNormaliser(const float& leftMel,
const float& rightMel,
bool useHTKMethod) override;
} /* namespace audio */
} /* namespace app */
} /* namespace arm */