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librosa.core.phase_vocoder¶

librosa.core.phase_vocoder(D, rate, hop_length=None)[source]¶

Phase vocoder. Given an STFT matrix D, speed up by a factor of rate

Based on the implementation provided by [1].

Note

This is a simplified implementation, intended primarily for reference and pedagogical purposes. It makes no attempt to handle transients, and is likely to produce many audible artifacts. For a higher quality implementation, we recommend the RubberBand library [2] and its Python wrapper pyrubberband.

1: Ellis, D. P. W. “A phase vocoder in Matlab.” Columbia University, 2002. http://www.ee.columbia.edu/~dpwe/resources/matlab/pvoc/
2: https://breakfastquay.com/rubberband/

Parameters

Dnp.ndarray [shape=(d, t), dtype=complex]

STFT matrix

ratefloat > 0 [scalar]

Speed-up factor: rate > 1 is faster, rate < 1 is slower.

hop_lengthint > 0 [scalar] or None

The number of samples between successive columns of D.

If None, defaults to n_fft/4 = (D.shape[0]-1)/2

Returns

D_stretchednp.ndarray [shape=(d, t / rate), dtype=complex]: time-stretched STFT

See also

pyrubberband

Examples

>>> # Play at double speed
>>> y, sr   = librosa.load(librosa.util.example_audio_file())
>>> D       = librosa.stft(y, n_fft=2048, hop_length=512)
>>> D_fast  = librosa.phase_vocoder(D, 2.0, hop_length=512)
>>> y_fast  = librosa.istft(D_fast, hop_length=512)

>>> # Or play at 1/3 speed
>>> y, sr   = librosa.load(librosa.util.example_audio_file())
>>> D       = librosa.stft(y, n_fft=2048, hop_length=512)
>>> D_slow  = librosa.phase_vocoder(D, 1./3, hop_length=512)
>>> y_slow  = librosa.istft(D_slow, hop_length=512)