zita-j2a - Use ALSA capture device as a Jack client, with resampling.
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
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
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
-h Display this text
ALSA playback device [none]
Sample rate 
Period size 
Number of fragments 
Number of channels 
Resampling quality 
-v Print tracing information [off]
Use '-h' to see all options.
A quick guide is available at
zita-ajbridge was written by Fons Adriaensen <firstname.lastname@example.org>.
This manual page was written by Robin Gareus <email@example.com> 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)