[linux-audio-user] Few questions on audio technologies

Tristan Van Berkom tristan.van.berkom at gmail.com
Tue Mar 22 16:16:27 EST 2005

On Tue, 22 Mar 2005 11:31:02 +0000, Steve Harris
<S.W.Harris at ecs.soton.ac.uk> wrote:
> > - Is JACK a suitable place to implement entire audio pipelines ?
> >   (i.e. if I have one "jack client" for each link in the pipeline; one
> >   reading an mp3 file, another decoding the mp3 file and outputting
> >   pcm data and another one creating FFT data for other purposes etc.)
> No. In particular sending FFT data over JACK will be tricky.
> I would only use JACK for PCM i/o, and do everything else with some other
> IPC.
> > - Is ALSA capable of really "mixing" or does it only route available
> >   commands supported by the hardware ?
> Goggle for dmix. If you care about this though, JACK is probably better.

Thanks alot for your reply ;-)

I do care; this is also why I'm wondering if JACK will turn out to be
an unneeded overhead or not, also I'd like to make sure that I can make
the most of whatever sound-card features will be available.

So far the plusses for using JACK is:
    - Simpler API for audio output (simpler than raw alsa lib)
    - Integrated mixing of streams
    - Renders audio capture practicly transperent.

That being said, my concerns are:
    - Having an intermediate daemon application between the streaming
      application and the kernel will definitly cause a significant overhead
      in terms of context switches. Although JACK brags of handleing 
      these context switches and scheduling in a clean and thought out 
      fashion; I'll only have one application to stream from, the that defeats 
      the purpose of /scheduling/ it.
    - Using JACK as a stream mixer may bring us further away from
      the metal than we'd like to be, 
        *  does "dmix" make use of any of the sound card's features to perform
           multi-stream mixing ?
        *  does JACK ?

    So far I think that JACK will simplify the project alot, I just
have to figure
out how many cpu cycles it will cost and if we can save those cycles by 
writing code ;-)


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