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python-stretch: pitch shifting and time stretching

A simple Python Wrapper of the Signalsmith Stretch C++ library for pitch and time stretching.

Features

• Time stretching
• Pitch shifting
• Multichannel support: Works with mono and multichannel audio files.
• Seamless integration: Works natively with NumPy arrays for compatibility with libraries such as librosa and many others used in audio processing pipelines.

Installation

python-stretch is available in PyPI (via Platform Wheels):

pip install python-stretch

Alternatevly, you can easly build it from source (You need a c++ compiler and cmake).

# Clone from github
git clone --recurse-submodules https://github.com/gregogiudici/python-stretch.git
# Install
pip install ./python-stretch

Examples

Quick Start

import numpy as np
import librosa
import python_stretch as ps

# Load an audio example from librosa (e.g., 'trumpet', 'brahms',...)
audio, sr = librosa.load(librosa.ex('trumpet'), sr=None)

# Assure that "audio" is a 2d array
if (audio.ndim == 1):
    audio = audio[np.newaxis, :]

# Create a Stretch object
stretch = ps.Signalsmith.Stretch()
# Configure using a preset
stretch.preset(audio.shape[0], sr) # numChannels, sampleRate
# Shift up by one octave
stretch.setTransposeSemitones(12)
# Stretch time
stretch.timeFactor = 0.75

# Process
audio_processed = stretch.process(audio)

# Save and listen
import soundfile as sf
sf.write("audio_original.wav", np.squeeze(audio), sr)
sf.write("audio_processed.wav", np.squeeze(audio_processed), sr)

Acknowledgements

• Signalsmith Stretch: python-stretch is built on top of the Signalsmith Stretch C++ library, which provides the core algorithms for time stretching and pitch shifting.
• nanobind: This project utilizes nanobind for easily binding the C++ code to Python.