Re: Multiple asynchronous JACK chains resampled?

Jonathan Brickman <jeb@xxxxxxxxxxxxxxxx> · Tue, 23 Feb 2016 10:38:50 -0600



              What I want to do,
                is to use the resources I have to run multiple signal
                generation and processing chains asynchronously, in
                parallel, and then use the final
                audio-hardware-synchronized chain to resample them all
                into one, perhaps using the Zita tools.  Anyone know if
                this is possible?  I saw this flow structure work very
                well in the video domain, quite a few years ago.

              
            That's not what you want to do at all.

              
            JACK is designed to be a *synchronous* system. All
              clients process audio corresponding to the same period of
              time, precisely in sync with each other. You do not want
              to "resample them all into one", and certainly not with
              the zita tools. 

              
            A "correct" digital audio processing and/or synthesis
              environment consists of a single audio interface (or at
              least, a single digital sample ("word") clock). You can
              run any number of JACK clients, connected in arbitrary
              ways. But using multiple audio interfaces (which is what
              the zita tools are related to) is not  the right thing to
              do unless you are forced to by lack of funds or
              inappropriate hardware.

            
    I do understand that JACK is designed to be completely synchronous. 
    But a good pipelined architecture, can take multiple synchronous
    processing chains running independently (asynchronously to each
    other), and then merge them at the output end.  What I want to do is
    the equivalent using JACK at the synchronous level, so that I take
    advantage of more of my computing power.  Eventually I will want to
    do exactly the same using four or five RPi-compatibles, with just
    one of them having the audio output; but right now I have about 75%
    of my CPU and 6+ gigabytes of RAM not being touched, so clearly the
    testbed is waiting :-).  The video processing pipeline I saw a while
    ago used a proprietary bus (it was a while ago), I am thinking IP is
    probably the simplest now, over localhost within this box, and
    through a good switch whenever I start work on RPis (which is
    probably not soon but is worth contemplating).

    
    And to use the Zita tools, I was going to see if there was an
    audio-over-IP transport which delivered ALSA ports :-)  I don't
    quite remember, it has been about eight months since I looked.  If
    there is, I would expect the existing Zita tools would do
    wonderfully for the resampling connectors.  If not, I wonder what
    best to use for JACK-to-JACK resampling?

    
    -- 

      
        Jonathan E. Brickman   jeb@xxxxxxxxxxxxxxxx   (785)233-9977

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