alsaloop - command-line PCM loopback


alsaloop [-option] [cmd]


alsaloop allows create a PCM loopback between a PCM capture device and a PCM playback device. alsaloop supports multiple soundcards, adaptive clock synchronization, adaptive rate resampling using the samplerate library (if available in the system). Also, mixer controls can be redirected from one card to another (for example Master and PCM).


  • -h | --help
         Prints the help information.
  • -g <file> | --config=<file>
         Use given configuration file. The syntax of this file is simple: one line contains the command line options for one job. The '#' means comment and rest of line is ignored. Example: # First line - comment, second line - first job -C hw:1,0 -P hw:0,0 -t 50000 -T 1 # Third line - comment, fourth line - second job -C hw:1,1 -P hw:0,1 -t 40000 -T 2
  • -d | --daemonize
         Daemonize the main process and use syslog for messages.
  • -P <device> | --pdevice=<device>
         Use given playback device.
  • -C <device> | --cdevice=<device>
         Use given capture device.
  • -X <device> | --pctl=<device>
         Use given CTL device for playback.
  • -Y <device> | --cctl=<device>
         Use given CTL device for capture.
  • -l <latency> | --latency=<frames>
         Requested latency in frames.
  • -t <usec> | --tlatency=<usec>
         Requested latency in usec (1/1000000sec).
  • -f <format> | --format=<format>
         Format specification (usually S16_LE S32_LE). Use -h to list all formats. Default format is S16_LE.
  • -c <channels> | --channels=<channels>
         Channel count specification. Default value is 2.
  • -c <rate> | --rate=<rate>
         Rate specification. Default value is 48000 (Hz).
  • -n | --resample
         Allow rate resampling using alsa-lib.
  • -A <converter> | --samplerate=<converter>
         Use libsamplerate and choose a converter: 0 or sincbest - best quality 1 or sincmedium - medium quality 2 or sincfastest - lowest quality 3 or zerohold - hold zero samples 4 or linear - worst quality - linear resampling 5 or auto - choose best method
  • -B <size> | --buffer=<size>
         Buffer size in frames.
  • -E <size> | --period=<size>
         Period size in frames.
  • -s <secs> | --seconds=<secs>
         Duration of loop in seconds.
  • -b | --nblock
         Non-block mode (very early process wakeup). Eats more CPU.
  • -S <mode> | --sync=<mode>
         Sync mode specification for capture to playback stream: 0 or none - do not touch the stream 1 or simple - add or remove samples to keep both streams synchronized 2 or captshift - use driver for the capture device (if supported) to compensate the rate shift 3 or playshift - use driver for the playback device (if supported) to compensate the rate shift 4 or samplerate - use samplerate library to do rate resampling 5 or auto - automatically selects the best method in this order: captshift, playshift, samplerate, simple
  • -T <num> | --thread=<num>
         Thread number (-1 means create a unique thread). All jobs with same thread numbers are run within one thread.
  • -m <mixid> | --mixer=<midid>
         Redirect mixer control from the playback card to the capture card. Format of mixid is SRCID(PLAYBACK)[@DSTID(PLAYBACK)]: "name='Master Playback Switch'" "name='PCM Playback Volume'" Known attributes: name - control ID name index - control ID index device - control ID device subdevice - control ID subdevice iface - control ID interface numid - control ID numid
  • -O <ossmixid> | --ossmixer=<midid>
         Redirect mixer control from the OSS Mixer emulation layer (capture card) to the ALSA layer (capture card). Format of ossmixid is ALSAID[,INDEX]@OSSID: " " "PCM, " Known OSS attributes: VOLUME, BASS, TREBLE, SYNTH, PCM, SPEAKER, LINE, MIC, CD, IMIX, ALTPCM, RECLEV, IGAIN, OGAIN, LINE1, LINE2, LINE3, DIGITAL1, DIGITAL2, DIGITAL3, PHONEIN, PHONEOUT, VIDEO, RADIO, MONITOR
  • -v | --verbose
         Verbose mode. Use multiple times to increase verbosity.
  • -U | --xrun
         Verbose xrun profiling.
  • -W <timeout> | --wake=<timeout>
         Set process wake timeout.


  • alsaloop -C hw:0,0 -P hw:1,0 -t 50000


None known.


alsaloop is by Jaroslav Kysela < >. This document is by Jaroslav Kysela < >.