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

Paul Davis paul at linuxaudiosystems.com
Sun Dec 15 21:25:00 UTC 2002

>> >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.

>> 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 
>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.

>> >Anyway, in that other post, I think I said there *is* a relation
>> >between all of these, but I forgot to explain why:
>> >
>> >	* Audio device syncs to wordclock
>> >	* Sequencer uses audio for timing (nominal sample rate assumed)
>> >
>> >Note that both are just *sync* - not lock. If you wanted to sync
>> > with a VRC, you would most probably be using SMPTE instead of
>> > wordclock - and then, it would make a *lot* more sense to sync +
>> > lock the sequencer to that, and just let the audio interface do
>> > 48 kHz, or whatever you like.
>> 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).


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