alsaloop

Create audio loopback between ALSA devices.

TLDR

Loop audio from capture to playback device

$ alsaloop -C [hw:0,0] -P [hw:1,0]

Loop with specific sample rate

$ alsaloop -C [hw:0,0] -P [hw:1,0] -r [48000]

Loop with specific format

$ alsaloop -C [hw:0,0] -P [hw:1,0] -f [S16_LE]

Run in daemon mode

$ alsaloop -C [hw:0,0] -P [hw:1,0] -d

SYNOPSIS

alsaloop [-C capture] [-P playback] [-r rate] [-f format] [options]

alsaloop creates a loopback between an ALSA capture device and playback device. It reads audio from one device and writes it to another in real-time, useful for routing audio between different hardware interfaces.
The tool handles buffer management, sample rate conversion if needed, and attempts to maintain synchronization between devices.

PARAMETERS

-C device

Capture (input) device

-P device

Playback (output) device

-r rate

Sample rate in Hz

-f format

Sample format (S16LE, S24LE, S32_LE, etc.)

-c channels

Number of channels

-d, --daemonize

Run as daemon

-s seconds

Process time limit

-t ms

Loop latency in milliseconds

--sync mode

Sync mode: none, simple, captshift, playshift

CAVEATS

Latency depends on buffer sizes and hardware capabilities. Different sample rates between devices require resampling. CPU usage increases with lower latency settings.

HISTORY

alsaloop is part of the alsa-utils package, providing a simple tool for audio routing that complements the more complex ALSA loopback kernel module.