// kaldi-native-fbank/csrc/feature-window.cc
//
// Copyright (c) 2022 Xiaomi Corporation (authors: Fangjun Kuang)
// This file is copied/modified from kaldi/src/feat/feature-window.cc
#include "frontend/feature-window.h"
#include <cmath>
#include <limits>
#include <vector>
#ifndef M_2PI
#define M_2PI 6.283185307179586476925286766559005
#endif
namespace knf {
std::ostream &operator<<(std::ostream &os, const FrameExtractionOptions &opts) {
os << opts.ToString();
return os;
}
FeatureWindowFunction::FeatureWindowFunction(const FrameExtractionOptions &opts)
: window_(opts.WindowSize()) {
int32_t frame_length = opts.WindowSize();
CHECK_GT(frame_length, 0);
float *window_data = window_.data();
double a = M_2PI / (frame_length - 1);
for (int32_t i = 0; i < frame_length; i++) {
double i_fl = static_cast<double>(i);
if (opts.window_type == "hanning") {
window_data[i] = 0.5 - 0.5 * cos(a * i_fl);
} else if (opts.window_type == "sine") {
// when you are checking ws wikipedia, please
// note that 0.5 * a = M_PI/(frame_length-1)
window_data[i] = sin(0.5 * a * i_fl);
} else if (opts.window_type == "hamming") {
window_data[i] = 0.54 - 0.46 * cos(a * i_fl);
} else if (opts.window_type ==
"povey") { // like hamming but goes to zero at edges.
window_data[i] = pow(0.5 - 0.5 * cos(a * i_fl), 0.85);
} else if (opts.window_type == "rectangular") {
window_data[i] = 1.0;
} else if (opts.window_type == "blackman") {
window_data[i] = opts.blackman_coeff - 0.5 * cos(a * i_fl) +
(0.5 - opts.blackman_coeff) * cos(2 * a * i_fl);
} else {
LOG(FATAL) << "Invalid window type " << opts.window_type;
}
}
}
void FeatureWindowFunction::Apply(float *wave) const {
int32_t window_size = window_.size();
const float *p = window_.data();
for (int32_t k = 0; k != window_size; ++k) {
wave[k] *= p[k];
}
}
int64_t FirstSampleOfFrame(int32_t frame, const FrameExtractionOptions &opts) {
int64_t frame_shift = opts.WindowShift();
if (opts.snip_edges) {
return frame * frame_shift;
} else {
int64_t midpoint_of_frame = frame_shift * frame + frame_shift / 2,
beginning_of_frame = midpoint_of_frame - opts.WindowSize() / 2;
return beginning_of_frame;
}
}
int32_t NumFrames(int64_t num_samples,
const FrameExtractionOptions &opts,
bool flush /*= true*/) {
int64_t frame_shift = opts.WindowShift();
int64_t frame_length = opts.WindowSize();
if (opts.snip_edges) {
// with --snip-edges=true (the default), we use a HTK-like approach to
// determining the number of frames-- all frames have to fit completely
// into
// the waveform, and the first frame begins at sample zero.
if (num_samples < frame_length)
return 0;
else
return (1 + ((num_samples - frame_length) / frame_shift));
// You can understand the expression above as follows: 'num_samples -
// frame_length' is how much room we have to shift the frame within the
// waveform; 'frame_shift' is how much we shift it each time; and the
// ratio
// is how many times we can shift it (integer arithmetic rounds down).
} else {
// if --snip-edges=false, the number of frames is determined by rounding
// the
// (file-length / frame-shift) to the nearest integer. The point of
// this
// formula is to make the number of frames an obvious and predictable
// function of the frame shift and signal length, which makes many
// segmentation-related questions simpler.
//
// Because integer division in C++ rounds toward zero, we add (half the
// frame-shift minus epsilon) before dividing, to have the effect of
// rounding towards the closest integer.
int32_t num_frames = (num_samples + (frame_shift / 2)) / frame_shift;
if (flush) return num_frames;
// note: 'end' always means the last plus one, i.e. one past the last.
int64_t end_sample_of_last_frame =
FirstSampleOfFrame(num_frames - 1, opts) + frame_length;
// the following code is optimized more for clarity than efficiency.
// If flush == false, we can't output frames that extend past the end
// of the signal.
while (num_frames > 0 && end_sample_of_last_frame > num_samples) {
num_frames--;
end_sample_of_last_frame -= frame_shift;
}
return num_frames;
}
}
void ExtractWindow(int64_t sample_offset,
const std::vector<float> &wave,
int32_t f,
const FrameExtractionOptions &opts,
const FeatureWindowFunction &window_function,
std::vector<float> *window,
float *log_energy_pre_window /*= nullptr*/) {
CHECK(sample_offset >= 0 && wave.size() != 0);
int32_t frame_length = opts.WindowSize();
int32_t frame_length_padded = opts.PaddedWindowSize();
int64_t num_samples = sample_offset + wave.size();
int64_t start_sample = FirstSampleOfFrame(f, opts);
int64_t end_sample = start_sample + frame_length;
if (opts.snip_edges) {
CHECK(start_sample >= sample_offset && end_sample <= num_samples);
} else {
CHECK(sample_offset == 0 || start_sample >= sample_offset);
}
if (window->size() != frame_length_padded) {
window->resize(frame_length_padded);
}
// wave_start and wave_end are start and end indexes into 'wave', for the
// piece of wave that we're trying to extract.
int32_t wave_start = int32_t(start_sample - sample_offset);
int32_t wave_end = wave_start + frame_length;
if (wave_start >= 0 && wave_end <= wave.size()) {
// the normal case-- no edge effects to consider.
std::copy(wave.begin() + wave_start,
wave.begin() + wave_start + frame_length,
window->data());
} else {
// Deal with any end effects by reflection, if needed. This code will
// only
// be reached for about two frames per utterance, so we don't concern
// ourselves excessively with efficiency.
int32_t wave_dim = wave.size();
for (int32_t s = 0; s < frame_length; ++s) {
int32_t s_in_wave = s + wave_start;
while (s_in_wave < 0 || s_in_wave >= wave_dim) {
// reflect around the beginning or end of the wave.
// e.g. -1 -> 0, -2 -> 1.
// dim -> dim - 1, dim + 1 -> dim - 2.
// the code supports repeated reflections, although this
// would only be needed in pathological cases.
if (s_in_wave < 0)
s_in_wave = -s_in_wave - 1;
else
s_in_wave = 2 * wave_dim - 1 - s_in_wave;
}
(*window)[s] = wave[s_in_wave];
}
}
ProcessWindow(opts, window_function, window->data(), log_energy_pre_window);
}
static void RemoveDcOffset(float *d, int32_t n) {
float sum = 0;
for (int32_t i = 0; i != n; ++i) {
sum += d[i];
}
float mean = sum / n;
for (int32_t i = 0; i != n; ++i) {
d[i] -= mean;
}
}
float InnerProduct(const float *a, const float *b, int32_t n) {
float sum = 0;
for (int32_t i = 0; i != n; ++i) {
sum += a[i] * b[i];
}
return sum;
}
static void Preemphasize(float *d, int32_t n, float preemph_coeff) {
if (preemph_coeff == 0.0) {
return;
}
CHECK(preemph_coeff >= 0.0 && preemph_coeff <= 1.0);
for (int32_t i = n - 1; i > 0; --i) {
d[i] -= preemph_coeff * d[i - 1];
}
d[0] -= preemph_coeff * d[0];
}
void ProcessWindow(const FrameExtractionOptions &opts,
const FeatureWindowFunction &window_function,
float *window,
float *log_energy_pre_window /*= nullptr*/) {
int32_t frame_length = opts.WindowSize();
// TODO(fangjun): Remove dither
CHECK_EQ(opts.dither, 0);
if (opts.remove_dc_offset) {
RemoveDcOffset(window, frame_length);
}
if (log_energy_pre_window != NULL) {
float energy =
std::max<float>(InnerProduct(window, window, frame_length),
std::numeric_limits<float>::epsilon());
*log_energy_pre_window = std::log(energy);
}
if (opts.preemph_coeff != 0.0) {
Preemphasize(window, frame_length, opts.preemph_coeff);
}
window_function.Apply(window);
}
} // namespace knf