janitor

feature-window.cc (8701B)

---

 // 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 "kaldi-native-fbank/csrc/feature-window.h"
 
 #include <algorithm>
 #include <cmath>
 #include <limits>
 #include <vector>
 #include <cstddef>
 
 #include "kaldi-native-fbank/csrc/kaldi-math.h"
 
 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();
   KNF_CHECK_GT(frame_length, 0);
 
   float *window_data = window_.data();
 
   double a = M_2PI / (frame_length - 1);
   if (opts.window_type == "hann") {
     // see https://pytorch.org/docs/stable/generated/torch.hann_window.html
     // We assume periodic is true
     a = M_2PI / frame_length;
   }
 
   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 == "hann") {
       window_data[i] = 0.50 - 0.50 * 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 {
       KNF_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*/) {
   KNF_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) {
     KNF_CHECK(start_sample >= sample_offset && end_sample <= num_samples);
   } else {
     KNF_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;
 }
 
 void Dither(float *d, int32_t n, float dither_value) {
   if (dither_value == 0.0) {
     return;
   }
 
   RandomState rstate;
   for (int32_t i = 0; i < n; ++i) {
     d[i] += RandGauss(&rstate) * dither_value;
   }
 }
 
 static void Preemphasize(float *d, int32_t n, float preemph_coeff) {
   if (preemph_coeff == 0.0) {
     return;
   }
 
   KNF_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();
 
   if (opts.dither != 0.0) {
     Dither(window, frame_length, opts.dither);
   }
 
   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