ALSA_IO(1)                                                                                                            ALSA_IO(1)



NAME
       alsa_in, alsa_out - Jack clients that perform I/O with an alternate audio interface

SYNOPSIS
       alsa_in [options]
       alsa_out [options]


DESCRIPTION
       A  JACK  client  that  opens a specified audio interface (different to the one used by the JACK server, if any) and moves
       audio data between its JACK ports and the interface. alsa_in will provide data from the interface (potentially  for  cap-
       ture); alsa_out will deliver data to it (for playback).

       The audio interface used by alsa_in/alsa_out does not need to be synchronized with JACK backend (or the hardware it might
       be using).  alsa_in/alsa_out tries to resample the output stream in an attempt to compensate for drift  between  the  two
       clocks.

       As of jack-0.116.3 this works almost perfectly. It takes some time, to reach absolute resample-rate stability. So give it
       some minutes (its intended to be running permanently anyways)


OPTIONS
       -j  jack_client_name
              Set Client Name.

       -d  alsa_device
              Use this Soundcard.

       -v
              Verbose, prints out resample coefficient and other parameters useful for debugging,  every  500ms.   also  reports
              soft xruns.

       -i
              Instrumentation. This logs the 4 important parameters of the samplerate control algorithm every 1ms.  You can pipe
              this into a file, and plot it. Should only be necessary, if it does not work as expected, and we  need  to  adjust
              some  of  the obscure parameters, to make it work.  Find me on irc.freenode.org #jack in order to set this up cor-
              rectly.

       -c  channels
              Set Number of channels.

       -r  sample_rate
              Set sample_rate. The program resamples as necessary.  So you can connect a 44k1 jackd to a soundcard only support-
              ing 48k. (default is jack sample_rate)

       -p  period_size
              Set  the  period  size. It is not related to the jackd period_size.  Sometimes it affects the quality of the delay
              measurements.  Setting this lower than the jackd period_size will only work, if you use a higher number  of  peri-
              ods.

       -n  num_period
              Set number of periods. See note for period_size.

       -q  quality
              Set the quality of the resampler from 0 to 4. can significanly reduce cpu usage.

       -m  max_diff
              The  value  when  a soft xrun occurs. Basically the window, in which the dma pointer may jitter. I don't think its
              necessary to play with this anymore.

       -t  target_delay
              The delay alsa_io should try to approach. Same as for max_diff. It will be setup based on -p and -n which is  gen-
              erally sufficient.

       -s  smooth_array_size
              This  parameter  controls  the size of the array used for smoothing the delay measurement. Its default is 256.  If
              you use a pretty low period size, you can lower the CPU usage a bit by decreasing this  parameter.   However  most
              CPU time is spent in the resampling so this will not be much.

       -C  P Control Clamp
              If  you have a PCI card, then the default value (15) of this parameter is too high for -p64 -n2... Setting it to 5
              should fix that.  Be aware that setting this parameter too low, lets the hf noise on the  delay  measurement  come
              through onto the resamplerate, so this might degrade the quality of the output. (but its a threshold value, and it
              has been chosen, to mask the noise of a USB card, which has an amplitude which is 50 times higher than that  of  a
              PCI card, so 5 wont loose you any quality on a PCI card)


AUTHOR
       Torben Hohn




1.9.7                                                       May 2011                                                  ALSA_IO(1)