export function mel_filter_bank()

in src/utils/audio.js [250:305]

• 45 lines of code
• 11 McCabe index (conditional complexity)

export function mel_filter_bank(
    num_frequency_bins,
    num_mel_filters,
    min_frequency,
    max_frequency,
    sampling_rate,
    norm = null,
    mel_scale = "htk",
    triangularize_in_mel_space = false,
) {
    if (norm !== null && norm !== "slaney") {
        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);

    let filter_freqs = mel_to_hertz(mel_freqs, mel_scale);
    let fft_freqs; // frequencies of FFT bins in Hz

    if (triangularize_in_mel_space) {
        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 {
        fft_freqs = linspace(0, Math.floor(sampling_rate / 2), num_frequency_bins);
    }

    const mel_filters = _create_triangular_filter_bank(fft_freqs, filter_freqs);

    if (norm !== null && norm === "slaney") {
        // Slaney-style mel is scaled to be approx constant energy per channel
        for (let i = 0; i < num_mel_filters; ++i) {
            const filter = mel_filters[i];
            const enorm = 2.0 / (filter_freqs[i + 2] - filter_freqs[i]);
            for (let j = 0; j < num_frequency_bins; ++j) {
                // Apply this enorm to all frequency bins
                filter[j] *= enorm;
            }
        }
    }

    // TODO warn if there is a zero row

    return mel_filters;

}