SoundCard 0.3.2

Play and record audio without resorting to CPython extensions

SoundCard is a library for playing and recording audio without resorting to a CPython extension. Instead, it is implemented using the wonderful CFFI and the native audio libraries of Linux, Windows and macOS.

SoundCard is cross-platform, and supports Linux/pulseaudio, Mac/coreaudio, and Windows/WASAPI. While the programming interface is identical across platforms, sound card naming schemes and default block sizes can vary between devices and platforms.

SoundCard is still in development. All major features work on all platforms, but there are a few known issues that still need to be fixed. If you find a bug, please open an Issue, and I will try to fix it. Or open a Pull Request, and I will try to include your fix into SoundCard.

However, please be aware that this is a hobby project of mine that I am developing for free, and in my spare time. While I try to be as accomodating as possible, I can not guarantee a timely response to issues. Publishing Open Source Software on Github does not imply an obligation to fix your problem right now. Please be civil.

SoundCard is licensed under the terms of the BSD 3-clause license

(c) 2016 Bastian Bechtold

Tutorial

Here is how you get to your Speakers and Microphones:

import soundcard as sc

# get a list of all speakers:
speakers = sc.all_speakers()
# get the current default speaker on your system:
default_speaker = sc.default_speaker()
# get a list of all microphones:
mics = sc.all_microphones()
# get the current default microphone on your system:
default_mic = sc.default_microphone()

# search for a sound card by substring:
>>> sc.get_speaker('Scarlett')
<Speaker Focusrite Scarlett 2i2 (2 channels)>
>>> one_mic = sc.get_microphone('Scarlett')
<Microphone Focusrite Scalett 2i2 (2 channels)>
# fuzzy-search to get the same results:
one_speaker = sc.get_speaker('FS2i2')
one_mic = sc.get_microphone('FS2i2')

All of these functions return Speaker and Microphone objects, which can be used for playback and recording. All data passed in and out of these objects are frames × channels Numpy arrays.

import numpy

>>> print(default_speaker)
<Speaker Focusrite Scarlett 2i2 (2 channels)>
>>> print(default_mic)
<Microphone Focusrite Scarlett 2i2 (2 channels)>

# record and play back one second of audio:
data = default_mic.record(samplerate=48000, numframes=48000)
default_speaker.play(data/numpy.max(data), samplerate=48000)

# alternatively, get a `Recorder` and `Player` object
# and play or record continuously:
with default_mic.recorder(samplerate=48000) as mic, \
      default_speaker.player(samplerate=48000) as sp:
    for _ in range(100):
        data = mic.record(numframes=1024)
        sp.play(data)

Latency

By default, SoundCard records and plays at the operating system’s default configuration. Particularly on laptops, this configuration might have extreme latencies, up to multiple seconds.

In order to request lower latencies, pass a blocksize to player or recorder. This tells the operating system your desired latency, and it will try to honor your request as best it can. On Windows/WASAPI, setting exclusive_mode=True might help, too (this is currently experimental).

Another source of latency is in the record function, which buffers output up to the requested numframes. In general, for optimal latency, you should use a numframes significantly lower than the blocksize above, maybe by a factor of two or four.

To get the audio data as quickly as absolutely possible, you can use numframes=None, which will return whatever audio data is available right now, without any buffering. Note that this might receive different numbers of frames each time.

With the above settings, block sizes of 256 samples or ten milliseconds are usually no problem. The total latency of playback and recording is dependent on how these buffers are handled by the operating system, though, and might be significantly higher.

Channel Maps

Some professional sound cards have large numbers of channels. If you want to record or play only a subset of those channels, you can specify a channel map. For playback, a channel map of [0, 3, 4] will play three-channel audio data on the physical channels one, four, and five. For recording, a channel map of [0, 3, 4] will return three-channel audio data recorded from the physical channels one, four, and five.

In addition, pulseaudio/Linux defines channel -1 as the mono mix of all channels for both playback and recording. CoreAudio/macOS defines channel -1 as silence for both playback and recording.

Known Issues:

• Windows/WASAPI currently records garbage if you record only a single channel. The reason for this is yet unknown. Multi-channel and channel maps work, though.

• Windows/WASAPI silently ignores the blocksize in some cases. Apparently, it only supports variable block sizes in exclusive mode.

• Error messages often report some internal CFFI/backend errors. This will be improved in the future.

Changelog

• 2018-04-25 implements fixed block sizes when recording (thank you, Pariente Manuel!)

• 2018-05-10 adds a test suite and various fixes for Windows

• 2018-05-11 various fixes for macOS

• 2018-06-27 Adds latency property to Linux/pulseaudio (Thank you, Pariente Manuel!)

• 2018-07-17 adds loopback support for Windows (Thank you, Jan Leskovec!)

• 2018-10-16 adds bug fix for IPython on Windows (Thank you, Sebastian Michel!)

• 2018-11-28 adds Sphinx/Readthedocs documentation

• 2019-03-25 adds support for Python 3.5 (Thank you, Daniel R. Kumor!)

• 2019-04-29 adds experimental support for exclusive mode on Windows