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/*
* 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.
*/
#include "AdMelSpectrogram.hpp"
#include "PlatformMath.hpp"
namespace arm {
namespace app {
namespace audio {
bool AdMelSpectrogram::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)
{
const size_t numBanks = melEnergies.size();
if (numBanks != filterBankFilterFirst.size() ||
numBanks != filterBankFilterLast.size()) {
printf_err("unexpected filter bank lengths\n");
return false;
}
for (size_t bin = 0; bin < numBanks; ++bin) {
auto filterBankIter = melFilterBank[bin].begin();
float melEnergy = 1e-10; /* Avoid log of zero at later stages. */
const int32_t firstIndex = filterBankFilterFirst[bin];
const int32_t lastIndex = filterBankFilterLast[bin];
for (int32_t i = firstIndex; i <= lastIndex; ++i) {
melEnergy += (*filterBankIter++ * fftVec[i]);
}
melEnergies[bin] = melEnergy;
}
return true;
}
void AdMelSpectrogram::ConvertToLogarithmicScale(
std::vector<float>& melEnergies)
{
/* Container for natural logarithms of mel energies */
std::vector <float> vecLogEnergies(melEnergies.size(), 0.f);
/* Because we are taking natural logs, we need to multiply by log10(e).
* Also, for wav2letter model, we scale our log10 values by 10 */
constexpr float multiplier = 10.0 * /* default scalar */
0.4342944819032518; /* log10f(std::exp(1.0))*/
/* Take log of the whole vector */
math::MathUtils::VecLogarithmF32(melEnergies, vecLogEnergies);
/* Scale the log values. */
for (auto iterM = melEnergies.begin(), iterL = vecLogEnergies.begin();
iterM != melEnergies.end(); ++iterM, ++iterL) {
*iterM = *iterL * multiplier;
}
}
float AdMelSpectrogram::GetMelFilterBankNormaliser(
const float& leftMel,
const float& rightMel,
const bool useHTKMethod)
{
/* Slaney normalization for mel weights. */
return (2.0f / (AdMelSpectrogram::InverseMelScale(rightMel, useHTKMethod) -
AdMelSpectrogram::InverseMelScale(leftMel, useHTKMethod)));
}
} /* namespace audio */
} /* namespace app */
} /* namespace arm */
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