pitch_shift()

std::vector< double > MayaFlux::Kinesis::Discrete::pitch_shift	(	std::span< const double >	src,
		double	semitones,
		uint32_t	window_size = 2048,
		uint32_t	analysis_hop = 512
	)

Pitch-shift by resampling around a phase vocoder stretch.

Stretches by 1/pitch_ratio, then resamples back to the original length using linear interpolation. This preserves duration while shifting pitch, which is the standard phase vocoder pitch-shift approach.

Parameters

src	Input samples
semitones	Pitch shift in semitones (positive = up, negative = down)
window_size	FFT frame size
analysis_hop	Analysis hop

Returns

Pitch-shifted output, same length as src

Definition at line 282 of file Spectral.cpp.

{
    if (src.empty() || semitones == 0.0)
        return { src.begin(), src.end() };
 
    const double pitch_ratio = std::pow(2.0, semitones / 12.0);
    const double stretch_ratio = 1.0 / pitch_ratio;
 
    std::vector<double> stretched = phase_vocoder_stretch(src, stretch_ratio, window_size, analysis_hop);
 
    if (stretched.empty())
        return {};
 
    const size_t out_n = src.size();
    std::vector<double> out(out_n);
    const size_t in_n = stretched.size();
    const double step = static_cast<double>(in_n - 1) / static_cast<double>(out_n - 1);
 
    for (size_t i = 0; i < out_n; ++i) {
        const double pos = static_cast<double>(i) * step;
        const auto idx = static_cast<size_t>(pos);
        const size_t idx1 = std::min(idx + 1, in_n - 1);
        const double frac = pos - static_cast<double>(idx);
        out[i] = stretched[idx] + frac * (stretched[idx1] - stretched[idx]);
    }
 
    return out;
}

References phase_vocoder_stretch().

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