ALSALOOP(1)                          General Commands Manual                          ALSALOOP(1)

NAME
       alsaloop - command-line PCM loopback

SYNOPSIS
       alsaloop [-option] [cmd]

DESCRIPTION
       alsaloop  allows create a PCM loopback between a PCM capture device and a PCM playback de‐
       vice.

       alsaloop supports multiple soundcards, adaptive clock synchronization, adaptive  rate  re‐
       sampling  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).

OPTIONS
       -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 ig‐
              nored. 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='Another 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:

                "Master@VOLUME"
                "PCM,1@ALTPCM"

              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.

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

BUGS
       None known.

AUTHOR
       alsaloop is by Jaroslav Kysela <perex@perex.cz>.  This  document  is  by  Jaroslav  Kysela
       <perex@perex.cz>.

                                            5 Aug 2010                                ALSALOOP(1)

Usage: alsaloop [OPTION]...

-h,--help      help
-g,--config    configuration file (one line = one job specified)
-d,--daemonize daemonize the main process and use syslog for errors
-P,--pdevice   playback device
-C,--cdevice   capture device
-X,--pctl      playback ctl device
-Y,--cctl      capture ctl device
-l,--latency   requested latency in frames
-t,--tlatency  requested latency in usec (1/1000000sec)
-f,--format    sample format
-c,--channels  channels
-r,--rate      rate
-n,--resample  resample in alsa-lib
-A,--samplerate use converter (0=sincbest,1=sincmedium,2=sincfastest,
                               3=zerohold,4=linear)
-B,--buffer    buffer size in frames
-E,--period    period size in frames
-s,--seconds   duration of loop in seconds
-b,--nblock    non-block mode (very early process wakeup)
-S,--sync      sync mode(0=none,1=simple,2=captshift,3=playshift,4=samplerate,
                         5=auto)
-a,--slave     stream parameters slave mode (0=auto, 1=on, 2=off)
-T,--thread    thread number (-1 = create unique)
-m,--mixer      redirect mixer, argument is:
                    SRC_SLAVE_ID(PLAYBACK)[@DST_SLAVE_ID(CAPTURE)]
-O,--ossmixer   rescan and redirect oss mixer, argument is:
                    ALSA_ID@OSS_ID  (for example: "Master@VOLUME")
-e,--effect    apply an effect (bandpass filter sweep)
-v,--verbose   verbose mode (more -v means more verbose)
-w,--workaround use workaround (serialopen)
-U,--xrun      xrun profiling
-W,--wake      process wake timeout in ms
-z,--syslog    use syslog for errors

Recognized sample formats are: S8 U8 S16_LE S16_BE U16_LE U16_BE S24_LE S24_BE U24_LE U24_BE S32_LE S32_BE U32_LE U32_BE FLOAT_LE FLOAT_BE FLOAT64_LE FLOAT64_BE IEC958_SUBFRAME_LE IEC958_SUBFRAME_BE MU_LAW A_LAW IMA_ADPCM MPEG GSM S20_LE S20_BE U20_LE U20_BE SPECIAL S24_3LE S24_3BE U24_3LE U24_3BE S20_3LE S20_3BE U20_3LE U20_3BE S18_3LE S18_3BE U18_3LE U18_3BE G723_24 G723_24_1B G723_40 G723_40_1B DSD_U8 DSD_U16_LE DSD_U32_LE DSD_U16_BE

Tip #1 (usable 500ms latency, good CPU usage, superb xrun prevention):
  alsaloop -t 500000
Tip #2 (superb 1ms latency, but heavy CPU usage):
  alsaloop -t 1000