[gmpi] Re: Reqs 3.9. Time - opening arguments.1

  • From: Tim Hockin <thockin@xxxxxxxxxx>
  • To: gmpi@xxxxxxxxxxxxx
  • Date: Thu, 12 Feb 2004 13:28:52 -0800

On Thu, Feb 12, 2004 at 02:54:30PM -0500, Michael Stauffer wrote:
> >Does that answer that?
> 
> Yes, I think it does. Don't hosts have to handle all this already when
> they sync to an external master? If a host is sync'ed to midi clocks,

right - it's the same problem.

> The multiple-tempo-event-list-per-audio-frame model would only make sense
> if the tempo controller were working from a static tempo map so it could
> know ahead of time what the changes were going to be within an audio
> frame. That is, unless the 1-frame latency is used that Koen mentioned.
> Does that sound right?

I've always assumed a 1-block latency for realtime events.  Introducing
variable jitter just seems WRONG to me, though it is the host's choice..

> This makes me wonder about the audio-frame method for sending events to
> plugs. Why are events not sent via a separate method with smaller time
> resolution? I figure it's much easier to just package all audio data and
> events into one bundle and have a single callback/thread to handle the
> data.
> 
> Are there other reasons? Cuz otherwise, plugs could receive all midi and
> other control events at finer resolution in a separate callback thread,

Concurrency.  One of the things people complained loudly about was having to
do locking between the GUI thread and the DSP thread accessing the
parameters.  Now, one of the caveats in the reqs already is that we MAY have
to incur some concurrency.

IF gmpi provided a sane locking architecture....?

Complexity.

> with? e.g., how common is 512 samples at 44.1kHz? This yields ~10 msec
> frame latency, which isn't too horrible for tempo processing, especially
> if it's a small percentage of users who might not be as concerned about
> top performance anyway. I don't know. I'm wondering how much of an issue
> frame latencies are going to be as systems can handle smaller and smaller
> frames at higher resolutions. Or have I got things mixed up somehow?

I think low-latency is becoming more the norm, and micro-optimizing to
provide lower control latency is probably a bad idea.  

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