NAME

       zita-a2j, zita-j2a - Use ALSA device as a Jack client, with resampling.

SYNOPSIS

       zita-a2j [options]
       zita-j2a [options]

DESCRIPTION

       These two programs allow one to use an ALSA device as a Jack client, to provide additional capture (zita-
       a2j) or playback (zita-j2a) channels. Functionally they are equivalent to alsa_in and alsa_out that  come
       with Jack, but they will provide much better audio quality.

       The  resampling  ratio  will  typically  be  stable  within  a few parts per million 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 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.

       Resampling  is performed using the zita-resampler library. The -Q option sets the resampling quality. The
       parameter value is half the length (i.e. the  delay)  of  the  multiphase  filter  used  for  resampling,
       expressed in samples at the lower of the two sample rates. This mainly affects the shape of the frequency
       response near the Nyquist frequency. It is normally not necessary to use this option as an optimum  value
       depending both the sample rates is chosen automatically. The available range is 16..96.

       The -S option disables resampling. This requires that the device is synced via word-clock to the one used
       by Jack.

       The -L option forces the ALSA interface to 2 channels and 16-bit sample format. This may be required when
       a2j  or  j2a  is  used with ALSA's 'loop' device, if the other end doesn't accept more than 2 channels or
       floating point samples. This option must not be used otherwise.

       Both programs 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.

       Small  variations  in  these  numbers will be seen when Jack apps are started or stopped. This is normal.
       Anything else isn't - please report.

       When starting, and in case of major trouble, the 'Starting synchronisation' message will  be  printed.  A
       restart  can happen if there is a timeout on the Jack server, e.g. when 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.  This may interrupt the audio signal, but should otherwise not have any ill
       consequences nor require a restart.

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

OPTIONS

       -h     Print command line and options summary.

       -j <name>
              Jack client name [zita-a2j or zita-j2a].

       -d <device>
              ALSA 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 [auto].

       -S     Word clock sync, disable resampling.

       -I <samples> [0]
              (zita-a2j only) Latency correction. The value is added to the latency property  set  on  the  Jack
              ports.

       -O <samples> [0]
              (zita-j2a  only)  Latency  correction.  The value is added to the latency property set on the Jack
              ports.

       -L     Force 2 channels and 16-bit sample format.

       -v     Print tracing information.

AUTHOR

       The zita-a2j and zita-j2a programs were written by Fons Adriaensen  <fons@linuxaudio.org>.   This  manual
       page was written by Robin Gareus <robin@gareus.org> and Fons Adriaensen.

                                                    Sept 2013                                   ZITA-AJBRIDGE(1)