Subject: Re: [linux-audio-dev] XAP and Event Outputs
From: David Olofson (david_AT_olofson.net)
Date: Wed Dec 11 2002 - 00:29:11 EET
On Tuesday 10 December 2002 23.02, Paul Davis wrote:
> >Yes. Event/audio time is one thing, and musical time is something
> >completely different, although related.
>
> you've just defined "event time" to be the same as "audio time".
> thats a mistake, i think. there are some definite benefits to being
> able to define events' time in musical time as well.
Like what? Since we're talking about sample accurate timing, isn't
asking the host about the musical time for an event timestamp
sufficient for when you want that information?
Note that I'm talking about a low level communication protocol for
use in situations where you would otherwise use LADSPA style control
ports, or audio rate control streams. These are *not* events as
stored inside a sequencer.
> >Musical time can be a bit hairy to calculate, so I don't think
> > it's a good idea to do it all the time, and pass it to all
> > plugins.
>
> VST does this the right way. or rather, existing steinberg hosts
> do. they don't compute the information till a plugin asks for it.
> then they cache it for that "block", handing the same data to any
> other plugin.
Yes, that's exactly what I have in mind. I can't think of any other
sensible way of doing it.
> >What you want is a callback that gives you the musical time
> >corresponding to a timestamp, and probably a few other variants as
> >well.
>
> this isn't adequate. the VST time info struct contains pretty much
> no dead wood at all, IMHO.
Well, I didn't mean "musical time" as in "musical time and nothing
else". *heh*
The use of a callback, as opposed to passing something to plugins
whether they want it or not (which means you would have to calculate
the musical time, transport time, SMPTE time and whatnot for every
single sample), was the whole point.
//David Olofson - Programmer, Composer, Open Source Advocate
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