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. There should be no perceptible loss of
       quality at all. From version 0.6.0 it is also possible to disable resampling if the device
       is word-clock synced.

       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)