Audio - jasper-zanjani/dotfiles GitHub Wiki

ALSA

Advanced Linux Sound Architecture (ALSA) replaced the earlier "Open Sound System".Schatz

ALSA kernel modules are designed to offer an interface that "corresponds to that of the hardware" to keep the modules simple, and similar cards will offer a similar interface. They offer two interfaces: operational and configuration

Operational interface through the /dev/ tree, with 3 main types of devices

  • PCM for recording or playing digitized sound samples
  • CTL for manipulating the internal mixer and routing of the card
  • MIDI to control the MIDI port, if it exists
  • Optionally, sequencer devices may also exist if the card has a builtin sound synthesizer with an associated timer device

Status and configuration interface via the /proc/asound/ tree (ref amixer)

PCM devices come in two varieties: output and input and are numbered from 0, which is generally for analog multichannel sound.

Cards have input or output sockets, and the mixer is controlled by the CTL device and routes sound samples among devices and sockets.

Controls come in 3 types;

  • Playback controls are associated with an output device or copy (input-to-output) routes
  • Capture controls are associated with an input device or copy (output-to-input) routes
  • Feature controls drive features of the card or mixer, usually just a switch to enable or disable the feature, though some also have levels. The Master Volume control is the most typical example, which allows control of the internal amplifier feature of the card. A more interesting example is that of a 3d spatializer that can be represented by a switch to enable or disable it as well as two levels.

Typical channel assignments

  • 0: front left
  • 1: front right
  • 2: rear left
  • 3: rear right

PulseAudio

PulseAudio is a sound server for POSIX OSes and a fixture on many Linux distributions.

PulseAudio is built around sources and sinks (i.e. devices) connected to source outputs and sink inputs (streams)

  • Source is an input device that produces samples, usually running a thread with its own event loop, generating sample chunks which are posted to all connected source outputs
  • Source output is a recording stream which consumes samples from a source
  • Sink is an output device that consumes samples, usually running a thread with its own event loop mixing sample chunks from connect sink inputs
  • Sink input is a playback stream, connected to a sink and producing samples for it

alsamixer

Command-line mixer

amixer

Command-line mixer for ALSA sound card driver Schatz

Display simplified list of controls

amixer scontrols

Display full list of controls

amixer controls

Show information about a mixer device

amixer info

speaker-test

Test loudspeakers with a 2-speaker setup

speaker-test -c 2

Distributions Alpine Arch CentOS Clear CoreOS Fedora GNOME KDE Kali Mac OS X WSL Yocto Archive ar bzcat bzip2 bzless bzmore compress cpio dar gunzip gzcat gzip tar uncompress unxz unzip xz zcat zip zipcloak zipcmp zipdetails zipgrep zipinfo zipnote zipsplit
Audio alsamixer amixer speaker-test

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