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An audio library based on libsndfile, CFFI and NumPy

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SoundFile is an audio library based on libsndfile, CFFI and NumPy. Full documentation is available on

SoundFile can read and write sound files. File reading/writing is supported through libsndfile, which is a free, cross-platform, open-source (LGPL) library for reading and writing many different sampled sound file formats that runs on many platforms including Windows, OS X, and Unix. It is accessed through CFFI, which is a foreign function interface for Python calling C code. CFFI is supported for CPython 2.6+, 3.x and PyPy 2.0+. SoundFile represents audio data as NumPy arrays.

SoundFile is BSD licensed (BSD 3-Clause License).
(c) 2013, Bastian Bechtold

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Breaking Changes

SoundFile has evolved rapidly during the last few releases. Most notably, we changed the import name from import pysoundfile to import soundfile in 0.7. In 0.6, we cleaned up many small inconsistencies, particularly in the the ordering and naming of function arguments and the removal of the indexing interface.

In 0.8.0, we changed the default value of always_2d from True to False. Also, the order of arguments of the write function changed from write(data, file, ...) to write(file, data, ...).

In 0.9.0, we changed the ctype arguments of the buffer_* methods to dtype, using the Numpy dtype notation. The old ctype arguments still work, but are now officially deprecated.


SoundFile depends on the Python packages CFFI and NumPy, and the system library libsndfile.

In a modern Python, you can use pip install soundfile to download and install the latest release of SoundFile and its dependencies. On Windows and OS X, this will also install the library libsndfile. On Linux, you need to install libsndfile using your distribution’s package manager, for example sudo apt-get install libsndfile1.

If you are running on an unusual platform or if you are using an older version of Python, you might need to install NumPy and CFFI separately, for example using the Anaconda package manager or the Unofficial Windows Binaries for Python Extension Packages.

Read/Write Functions

Data can be written to the file using soundfile.write(), or read from the file using SoundFile can open all file formats that libsndfile supports, for example WAV, FLAC, OGG and MAT files (see Known Issues below about writing OGG files).

Here is an example for a program that reads a wave file and copies it into an FLAC file:

import soundfile as sf

data, samplerate ='existing_file.wav')
sf.write('new_file.flac', data, samplerate)

Block Processing

Sound files can also be read in short, optionally overlapping blocks with soundfile.blocks(). For example, this calculates the signal level for each block of a long file:

import numpy as np
import soundfile as sf

rms = [np.sqrt(np.mean(block**2)) for block in
       sf.blocks('myfile.wav', blocksize=1024, overlap=512)]

SoundFile Objects

Sound files can also be opened as soundfile.SoundFile objects. Every SoundFile has a specific sample rate, data format and a set number of channels.

If a file is opened, it is kept open for as long as the SoundFile object exists. The file closes when the object is garbage collected, but you should use the soundfile.SoundFile.close() method or the context manager to close the file explicitly:

import soundfile as sf

with sf.SoundFile('myfile.wav', 'r+') as f:
    while f.tell() < f.frames:
        pos = f.tell()
        data =

All data access uses frames as index. A frame is one discrete time-step in the sound file. Every frame contains as many samples as there are channels in the file.

RAW Files

Pysoundfile can usually auto-detect the file type of sound files. This is not possible for RAW files, though:

import soundfile as sf

data, samplerate ='myfile.raw', channels=1, samplerate=44100,

Note that on x86, this defaults to endian='LITTLE'. If you are reading big endian data (mostly old PowerPC/6800-based files), you have to set endian='BIG' accordingly.

You can write RAW files in a similar way, but be advised that in most cases, a more expressive format is better and should be used instead.

Virtual IO

If you have an open file-like object, Pysoundfile can open it just like regular files:

import soundfile as sf
with open('filename.flac', 'rb') as f:
    data, samplerate =

Here is an example using an HTTP request:

import io
import soundfile as sf
from urllib.request import urlopen

url = ""
data, samplerate =

Note that the above example only works with Python 3.x. For Python 2.x support, replace the third line with:

from urllib2 import urlopen

Known Issues

Writing to OGG files can result in empty files with certain versions of libsndfile. See #130 for news on this issue.


2013-08-27 V0.1.0 Bastian Bechtold:
Initial prototype. A simple wrapper for libsndfile in Python
2013-08-30 V0.2.0 Bastian Bechtold:
Bugfixes and more consistency with PySoundCard
2013-08-30 V0.2.1 Bastian Bechtold:
2013-09-27 V0.3.0 Bastian Bechtold:
Added binary installer for Windows, and context manager
2013-11-06 V0.3.1 Bastian Bechtold:
Switched from distutils to setuptools for easier installation
2013-11-29 V0.4.0 Bastian Bechtold:
Thanks to David Blewett, now with Virtual IO!
2013-12-08 V0.4.1 Bastian Bechtold:
Thanks to Xidorn Quan, FLAC files are not float32 any more.
2014-02-26 V0.5.0 Bastian Bechtold:
Thanks to Matthias Geier, improved seeking and a flush() method.
2015-01-19 V0.6.0 Bastian Bechtold:

A big, big thank you to Matthias Geier, who did most of the work!

  • Switched to float64 as default data type.
  • Function arguments changed for consistency.
  • Added unit tests.
  • Added global read(), write(), blocks() convenience functions.
  • Documentation overhaul and hosting on readthedocs.
  • Added 'x' open mode.
  • Added tell() method.
  • Added __repr__() method.
2015-04-12 V0.7.0 Bastian Bechtold:

Again, thanks to Matthias Geier for all of his hard work, but also Nils Werner and Whistler7 for their many suggestions and help.

  • Renamed import pysoundfile to import soundfile.
  • Installation through pip wheels that contain the necessary libraries for OS X and Windows.
  • Removed exclusive_creation argument to write.
  • Added truncate() method.
2015-10-20 V0.8.0 Bastian Bechtold:

Again, Matthias Geier contributed a whole lot of hard work to this release.

  • Changed the default value of always_2d from True to False.
  • Numpy is now optional, and only loaded for read and write.
  • Added SoundFile.buffer_read and SoundFile.buffer_read_into and SoundFile.buffer_write, which read/write raw data without involving Numpy.
  • Added info function that returns metadata of a sound file.
  • Changed the argument order of the write function from write(data, file, ...) to write(file, data, ...)

And many more minor bug fixes.

2017-02-02 V0.9.0 Bastian Bechtold:

Thank you, Matthias Geier, Tomas Garcia, and Todd, for contributions for this release.

  • Adds support for ALAC files.
  • Adds new member __libsndfile_version__
  • Adds number of frames to info class
  • Adds dtype argument to buffer_* methods
  • Deprecates ctype argument to buffer_* methods
  • Adds official support for Python 3.6

And some minor bug fixes.

2017-11-12 V0.10.0 Bastian Bechtold:

Thank you, Matthias Geier, Toni Barth, Jon Peirce, Till Hoffmann, and Tomas Garcia, for contributions to this release.

  • Should now work with cx_freeze.
  • Several documentation fixes in the README.
  • Removes deprecated ctype argument in favor of dtype in buffer_*().
  • Adds SoundFile.frames in favor of now-deprecated __len__().
  • Improves performance of blocks and SoundFile.blocks().
  • Improves import time by using CFFI’s out of line mode.
  • Adds a build script for building distributions.

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