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NAME

       zita-j2a - Use ALSA capture device as a Jack client, with resampling.

SYNOPSIS

       zita-j2a [options]

DESCRIPTION

       This tool allows one to use an ALSA device as a Jack client, to provide
       additional capture channels. Functionally it is equivalent to  alsa_out
       that comes with Jack, but provides much better audio quality.

       The  resampling  ratio will typically be stable within 1 PPM and change
       only very smoothly. Delay will be stable as well even under worse  case
       conditions, e.g. the Jack client running near the end of the cycle.

       The  alsa  device  should  be  a  'hw:'  one,  i.e.  direct access to a
       soundcard and not an ALSA 'plug' device. A well-working Jack system  is
       assumed, running in real-time mode.

       The  sample  rate can be the same as Jack's one, or different.  Minimum
       delay is obtained by running the alsa device at  a  lower  period  size
       than  Jack.  This  can  be done safely as the alsa thread will run at a
       higher priority, and apart from copying to/from an internal  buffer  no
       work  is  done  there.  There  are  no  restrictions  on the product of
       period_size  and  number_of_periods  as  there  are  for  alsa_in   and
       alsa_out.

       zita-j2a  will optionally print some information four times per second.
       The first number is the  average  loop  error  over  the  last  quarter
       second,  in samples. It should be reduced to small randowm values close
       to zero after 15 seconds or so. The second is  the  dynamic  correction
       factor of the nominal resampling ratio. This should converge to a value
       close to one and not move much.

       You may observe small variations in these numbers when  Jack  apps  are
       started  or  stopped.  This  is  normal.  Anything  else isn't - please
       report.

       When starting, and in case of major trouble, you will see the
        'Starting synchronisation' message. This can  happen  if  there  is  a
       timeout  on  the  Jack server, e.g. a client crashed or terminated in a
       dirty way. Jack1 will skip  one  or  more  cycles  when  new  apps  are
       started,  or when a large number of port connections is done in a short
       time.  his may interrupt the audio signal,  but  should  otherwise  not
       have any ill consequences nor require a restart.

       zita-a2j and zita-j2a will suspend operation while Jack is in
        'freewheeling' mode.

OPTIONS

       -h     Display this text

       -d <device>
              ALSA playback device [none]

       -r <rate>
              Sample rate [48000]

       -p <period>
              Period size [256]

       -n <nfrags>
              Number of fragments [2]

       -c <nchannels>
              Number of channels [2]

       -Q <quality>
              Resampling quality [48]

       -v     Print tracing information [off]

              Use '-h' to see all options.

SEE ALSO

       A          quick          guide         is         available         at
       <http://kokkinizita.linuxaudio.org/linuxaudio/zita-ajbridge-
       doc/quickguide.php>

AUTHOR

       zita-ajbridge was written by Fons Adriaensen <fons@linuxaudio.org>.

       This manual page was written by Robin Gareus <robin@gareus.org> for the
       Debian project (but may be  used  by  others).   It  is  based  on  the
       original README and announce message by Fons Adriaensen.

                                  March 2012                      ZITA-REV1(1)



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