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[audio utils] fix fft_bin_width computation #1274

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Merged
merged 1 commit into from
Apr 9, 2025
Merged

[audio utils] fix fft_bin_width computation #1274

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7 changes: 1 addition & 6 deletions src/models/audio_spectrogram_transformer/feature_extraction_audio_spectrogram_transformer.js
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Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@ export class ASTFeatureExtractor extends FeatureExtractor {

const sampling_rate = this.config.sampling_rate;
const mel_filters = mel_filter_bank(
256, // num_frequency_bins
257, // num_frequency_bins
this.config.num_mel_bins, // num_mel_filters
20, // min_frequency
Math.floor(sampling_rate / 2), // max_frequency
Expand All @@ -19,11 +19,6 @@ export class ASTFeatureExtractor extends FeatureExtractor {
"kaldi", // mel_scale
true, // triangularize_in_mel_space
);

// Do padding:
for (let i = 0; i < mel_filters.length; ++i) {
mel_filters[i].push(0);
}
this.mel_filters = mel_filters;

this.window = window_function(400, 'hann', {
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7 changes: 1 addition & 6 deletions src/models/seamless_m4t/feature_extraction_seamless_m4t.js
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Expand Up @@ -9,7 +9,7 @@ export class SeamlessM4TFeatureExtractor extends FeatureExtractor {

const sampling_rate = this.config.sampling_rate;
const mel_filters = mel_filter_bank(
256, // num_frequency_bins
257, // num_frequency_bins
this.config.num_mel_bins, // num_mel_filters
20, // min_frequency
Math.floor(sampling_rate / 2), // max_frequency
Expand All @@ -18,11 +18,6 @@ export class SeamlessM4TFeatureExtractor extends FeatureExtractor {
"kaldi", // mel_scale
true, // triangularize_in_mel_space
);

// Do padding:
for (let i = 0; i < mel_filters.length; ++i) {
mel_filters[i].push(0);
}
this.mel_filters = mel_filters;

this.window = window_function(400, 'povey', {
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7 changes: 1 addition & 6 deletions src/models/wespeaker/feature_extraction_wespeaker.js
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Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@ export class WeSpeakerFeatureExtractor extends FeatureExtractor {

const sampling_rate = this.config.sampling_rate;
const mel_filters = mel_filter_bank(
256, // num_frequency_bins
257, // num_frequency_bins
this.config.num_mel_bins, // num_mel_filters
20, // min_frequency
Math.floor(sampling_rate / 2), // max_frequency
Expand All @@ -19,11 +19,6 @@ export class WeSpeakerFeatureExtractor extends FeatureExtractor {
"kaldi", // mel_scale
true, // triangularize_in_mel_space
);

// Do padding:
for (let i = 0; i < mel_filters.length; ++i) {
mel_filters[i].push(0);
}
this.mel_filters = mel_filters;

this.window = window_function(400, 'hamming', {
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13 changes: 11 additions & 2 deletions src/utils/audio.js
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Original file line number Diff line number Diff line change
Expand Up @@ -235,7 +235,8 @@ function linspace(start, end, num) {
* various implementation exist, which differ in the number of filters, the shape of the filters, the way the filters
* are spaced, the bandwidth of the filters, and the manner in which the spectrum is warped. The goal of these
* features is to approximate the non-linear human perception of the variation in pitch with respect to the frequency.
* @param {number} num_frequency_bins Number of frequencies used to compute the spectrogram (should be the same as in `stft`).
* @param {number} num_frequency_bins Number of frequency bins (should be the same as `n_fft // 2 + 1`
* where `n_fft` is the size of the Fourier Transform used to compute the spectrogram).
* @param {number} num_mel_filters Number of mel filters to generate.
* @param {number} min_frequency Lowest frequency of interest in Hz.
* @param {number} max_frequency Highest frequency of interest in Hz. This should not exceed `sampling_rate / 2`.
Expand All @@ -261,6 +262,14 @@ export function mel_filter_bank(
throw new Error('norm must be one of null or "slaney"');
}

if (num_frequency_bins < 2) {
throw new Error(`Require num_frequency_bins: ${num_frequency_bins} >= 2`);
}

if (min_frequency > max_frequency) {
throw new Error(`Require min_frequency: ${min_frequency} <= max_frequency: ${max_frequency}`);
}

const mel_min = hertz_to_mel(min_frequency, mel_scale);
const mel_max = hertz_to_mel(max_frequency, mel_scale);
const mel_freqs = linspace(mel_min, mel_max, num_mel_filters + 2);
Expand All @@ -269,7 +278,7 @@ export function mel_filter_bank(
let fft_freqs; // frequencies of FFT bins in Hz

if (triangularize_in_mel_space) {
const fft_bin_width = sampling_rate / (num_frequency_bins * 2);
const fft_bin_width = sampling_rate / ((num_frequency_bins - 1) * 2);
fft_freqs = hertz_to_mel(Float64Array.from({ length: num_frequency_bins }, (_, i) => i * fft_bin_width), mel_scale);
filter_freqs = mel_freqs;
} else {
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