Re: [Jack-Devel] JACK Capabilities

On Tue, Apr 12, 2011 at 01:54:35PM +0200, Hampiholi, Vallabha Vasant wrote:

> I know I should have gone through the mail archives before posting
> this message, but due to the urgency of the project I am going to post
> a few queries. Please link me to the archives if required.


You're looking for http://jackaudio.org/documentation

> We are evaluating two of the popular audio servers for a project
> namely JACK and PulseAudio.

Just to get this right: PulseAudio is consumer grade (think of playback)
while JACK is more on the producer side. Some may find this
oversimplifying, but usually you don't want non-audio experts to run
jackd. It's mainly for studios, broadcasting and live setups.

> 1.       Is there a source and sink concept like in PA or GStreamer?
> If so can any source connect to any compatible sink?

Yes (to both questions)

> 2.       Does JACK have an inbuilt Sample Rate Converter? Say for
> example data is flowing from one JACK client to another each with
> different Sample Rate, will the SR conversion be taken care of by
> JACK?

There are no different sample rates, all jack clients run at the same
samplerate.

> 3.       Are there separate channels for data and command flow? Data
> can be audio stream and command could be something like play, pause
> etc.

Basically, there's only data flow and no commands. You can, to some
degree, emit play/pause commands, but they don't necessarily affect all
clients, only those who have a notion of time/bars like Logic or Cubase.

> 4.       Does it support block processing?

Block processing? You'll get a callback for each N samples, were N is a
power of two. If this is a block, then yes, it does block processing.

> 5.       When I set a particular volume, bass, treble etc settings and
> then when I restart does JACK load the previous settings?

Jack has no notion of volumes, bass, treble or whatsoever. Jack just
routes audio from sinks to sources. It has session support, so if the
sink knows how to handle this session data and restores all the
settings, then it would be persisent. Note that this doesn't hold true
for the ALSA "sinks" at the moment, and I guess it never will.

> 6.       Does JACK come with some diagnosis tools? DEBUG, ERROR messages etc?

Sort of. There's verbose mode, telling you if something's wrong.


> Finally to get a start on JACK where should I start?

The documentation link I've posted above. And see the example-clients
directory.


Cheers

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