/**
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* Copyright (c) 2022 Xiaomi Corporation (authors: Fangjun Kuang)
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*
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* See LICENSE for clarification regarding multiple authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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// This file is copied/modified from kaldi/src/feat/mel-computations.h
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#ifndef KALDI_NATIVE_FBANK_CSRC_MEL_COMPUTATIONS_H_
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#define KALDI_NATIVE_FBANK_CSRC_MEL_COMPUTATIONS_H_
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#include <cmath>
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#include <string>
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#include <utility>
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#include <vector>
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#include "kaldi-native-fbank/csrc/feature-window.h"
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namespace knf {
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struct MelBanksOptions {
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int32_t num_bins = 25; // e.g. 25; number of triangular bins
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float low_freq = 20; // e.g. 20; lower frequency cutoff
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// an upper frequency cutoff; 0 -> no cutoff, negative
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// ->added to the Nyquist frequency to get the cutoff.
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float high_freq = 0;
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float vtln_low = 100; // vtln lower cutoff of warping function.
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// vtln upper cutoff of warping function: if negative, added
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// to the Nyquist frequency to get the cutoff.
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float vtln_high = -500;
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bool debug_mel = false;
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// htk_mode is a "hidden" config, it does not show up on command line.
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// Enables more exact compatibility with HTK, for testing purposes. Affects
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// mel-energy flooring and reproduces a bug in HTK.
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bool htk_mode = false;
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std::string ToString() const {
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std::ostringstream os;
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os << "num_bins: " << num_bins << "\n";
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os << "low_freq: " << low_freq << "\n";
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os << "high_freq: " << high_freq << "\n";
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os << "vtln_low: " << vtln_low << "\n";
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os << "vtln_high: " << vtln_high << "\n";
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os << "debug_mel: " << debug_mel << "\n";
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os << "htk_mode: " << htk_mode << "\n";
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return os.str();
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}
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};
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std::ostream &operator<<(std::ostream &os, const MelBanksOptions &opts);
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class MelBanks {
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public:
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static inline float InverseMelScale(float mel_freq) {
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return 700.0f * (expf(mel_freq / 1127.0f) - 1.0f);
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}
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static inline float MelScale(float freq) {
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return 1127.0f * logf(1.0f + freq / 700.0f);
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}
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static float VtlnWarpFreq(
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float vtln_low_cutoff,
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float vtln_high_cutoff, // discontinuities in warp func
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float low_freq,
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float high_freq, // upper+lower frequency cutoffs in
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// the mel computation
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float vtln_warp_factor, float freq);
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static float VtlnWarpMelFreq(float vtln_low_cutoff, float vtln_high_cutoff,
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float low_freq, float high_freq,
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float vtln_warp_factor, float mel_freq);
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// TODO(fangjun): Remove vtln_warp_factor
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MelBanks(const MelBanksOptions &opts,
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const FrameExtractionOptions &frame_opts, float vtln_warp_factor);
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/// Compute Mel energies (note: not log energies).
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/// At input, "fft_energies" contains the FFT energies (not log).
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///
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/// @param fft_energies 1-D array of size num_fft_bins/2+1
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/// @param mel_energies_out 1-D array of size num_mel_bins
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void Compute(const float *fft_energies, float *mel_energies_out) const;
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int32_t NumBins() const { return bins_.size(); }
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private:
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// center frequencies of bins, numbered from 0 ... num_bins-1.
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// Needed by GetCenterFreqs().
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std::vector<float> center_freqs_;
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// the "bins_" vector is a vector, one for each bin, of a pair:
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// (the first nonzero fft-bin), (the vector of weights).
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std::vector<std::pair<int32_t, std::vector<float>>> bins_;
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// TODO(fangjun): Remove debug_ and htk_mode_
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bool debug_;
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bool htk_mode_;
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};
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} // namespace knf
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#endif // KALDI_NATIVE_FBANK_CSRC_MEL_COMPUTATIONS_H_
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