Introduction

Author:

Casper Wilstrup <cwi@aves.dk>

Author:

Lars Immisch <lars@ibp.de>

This software is licensed under the PSF license - the same one used by the majority of the python distribution. Basically you can use it for anything you wish (even commercial purposes). There is no warranty whatsoever.

Abstract

This package contains wrappers for accessing the ALSA API from Python. It is currently fairly complete for PCM devices and Mixer access. MIDI sequencer support is low on our priority list, but volunteers are welcome.

If you find bugs in the wrappers please use the github issue tracker. Please don’t send bug reports regarding ALSA specifically. There are several bugs in this API, and those should be reported to the ALSA team - not me.

What is ALSA

The Advanced Linux Sound Architecture (ALSA) provides audio and MIDI functionality to the Linux operating system.

Logically ALSA consists of these components:

• A set of kernel drivers. — These drivers are responsible for handling the physical sound hardware from within the Linux kernel, and have been the standard sound implementation in Linux since kernel version 2.5

• A kernel level API for manipulating the ALSA devices.

• A user-space C library for simplified access to the sound hardware from userspace applications. This library is called libasound and is required by all ALSA capable applications.

More information about ALSA may be found on the project homepage http://www.alsa-project.org

ALSA and Python

The older Linux sound API (OSS) – which is now deprecated – is well supported by the standard Python library, through the ossaudiodev module. No native ALSA support exists in the standard library.

There are a few other “ALSA for Python” projects available, including at least two different projects called pyAlsa. Neither of these seem to be under active development at the time - and neither are very feature complete.

I wrote PyAlsaAudio to fill this gap. My long term goal is to have the module included in the standard Python library, but that looks currently unlikely.

PyAlsaAudio has full support for sound capture, playback of sound, as well as the ALSA Mixer API.

MIDI support is not available, and since I don’t own any MIDI hardware, it’s difficult for me to implement it. Volunteers to work on this would be greatly appreciated.

Installation

Note: the wrappers link with the alsasound library (from the alsa-lib package) and need the ALSA headers for compilation. Verify that you have /usr/lib/libasound.so and /usr/include/alsa (or similar paths) before building.

On Debian (and probably Ubuntu), install libasound2-dev.

Naturally you also need to use a kernel with proper ALSA support. This is the default in Linux kernel 2.6 and later. If you are using kernel version 2.4 you may need to install the ALSA patches yourself - although most distributions ship with ALSA kernels.

To install, execute the following: —

$ python setup.py build

And then as root: —

# python setup.py install

Testing

Make sure that aplay plays a file through the soundcard you want, then try:

$ python playwav.py <filename.wav>

If aplay needs a device argument, like aplay -D hw:CARD=sndrpihifiberry,DEV=0, use:

$ python playwav.py -d hw:CARD=sndrpihifiberry,DEV=0 <filename.wav>

To test PCM recordings (on your default soundcard), verify your microphone works, then do:

$ python recordtest.py -d <device> <filename>

Speak into the microphone, and interrupt the recording at any time with Ctl-C.

Play back the recording with:

$ python playbacktest.py -d <device> <filename>

There is a minimal test suite in test.py, but it is a bit dependent on the ALSA configuration and may fail without indicating a real problem.

If you find bugs/problems, please file a bug report.