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 inter‐
       face  (potentially  for capture); alsa_out will deliver data to it (for
       playback).

       The audio interface used by alsa_in/alsa_out does not need to  be  syn‐
       chronized  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 correctly.

       -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  supporting  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 periods.

       -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  generally	suffi‐
	      cient.

       -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	resam‐
	      pling 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  resampler‐
	      ate, 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

1.9.8				 February 2014			    ALSA_IO(1)

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