[linux-audio-dev] XAP and these <MEEP> timestamps...

David Olofson david at olofson.net
Sun Dec 15 22:25:01 UTC 2002


On Monday 16 December 2002 03.22, Paul Davis wrote:
> >> >Positional data sort of implies that you can extract timing
> >> > data as well, provided you get a stream of positional data
> >> > with sufficiently accurate timing.
> >>
> >> no, you can't. how rapidly we are moving through a series of
> >> events on a timeline has nothing to do with how many samples per
> >> second we expect to process.
> >
> >Who said anything about samples/second?
>
> just an example unit. you can't get any information about a
> continuously flowing time by watching non-monotonic, discontinuous
> positional data.

No, you're right, of course. It's just that if the information comes 
at regular intervals and with reasonably accurate timing, you can 
"guess" the relative speed of time where they come from, by looking 
at two or more events. If you don't get at least few hundred messages 
per second, what else can you do?


> >> we could be playing something at half-speed, for
> >> example, or scrubbing using an MTC/MMC/SMPTE power jog wheel.
> >
> >Sure, that's exactly what I'm thinking about. You're suggesting
> > that you *must* wait for each positional "event" before you do
> > anything at all?
> >
> >What I'm talking about is just what every reasonably well written
> >sequencer does when you tell it to lock to something.
>
> no, i didn't mean anything but that. its just that unless you know
> that the positional data is "not normal", its useless as a time
> reference. you can certainly lock to it, and move along the
> timeline based on your current notion of direction and speed. you
> just have to be ready for that to be revised at any time, and for
> the current position to change in arbitrary ways at any time.

Yes indeed - that's exactly what I meant, but I seem to be using the 
wrong terms all the time... :-/


[...]
> >> see above. you're confusing two entirely separate types of
> >> synchronization.
> >
> >Confusing what with what? You can't sync a sequencer to a VCR, and
> >let the audio interface (for the softsynths, or whatever) run at a
> >fixed sample rate? Seems to work really rather well if the "audio
> >interface" is built into an external MIDI synth, that doesn't sync
> > or lock to anything it all...
>
> of course you can do that. the point is that the SMPTE sync between
> the VCR and the sequencer is completely unrelated to the "sync"
> used by the audio interface (its own clock source, for example, or
> wordclock).

Well, yes. The former is positional, while the latter only affects 
the sample rate, or "speed". If it still sounds like I'm taking those 
for equivalent, I think I'd better STFU and learn english.


//David Olofson - Programmer, Composer, Open Source Advocate

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