PaddleSpeech/runtime/engine/common/frontend/feature-window.cc

// 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