[gmpi] Re: 3.9 Time Formats

  • From: "Michael Stauffer" <michael@xxxxxxxxxxxxxxxxxx>
  • To: <gmpi@xxxxxxxxxxxxx>
  • Date: Tue, 17 Feb 2004 15:29:48 -0500

Tim wrote:

>> >What I don't get is this:  Given that there is a significant
>> >chance that any
>> >lookahead will be *wrong*, why do it at all?  Why do people
>> >keep insisting on
>> >it?  I mean, I'm not AGAINST it, if it can be justified.
>But if it is
>> >unreliable AT BEST, what's the point?
>> If the host is not accepting tempo input from anywhere else
>(or depending
>> on how it's all set up, if there's just a single tempo controller that
>> has a *static* tempo map posted and designated for use), then
>> will not be wrong. Ie, if there's a single static tempo map somewhere
>> that's being used during performance, there's no chance it
>will change. I
>> figure this is a common scenario.
>That's a big set of "if"s.  I would think it would be more
>common for a host
>to always provide the option to change the tempo, rather than

Well it's really just one "if": when there's a single tempo source and
it's a static tempo map, ie the host is in *internal* sync mode (or
there's a single static tempo map from a GMPI plug if things get that
involved with GMPI).

When the host is in *external* sync mode (whether it be sync from clocks,
ReWire, or a plug) it's in a signifigantly different operating mode, and
tempo lookahead would be meaningless.

I just tried it in Sonar. When it's in *internal* sync mode it plays
using the current static tempo map. I can change tempo and insert tempos
while it's playing, but the playback cuts out while Sonar readjusts,
which is what Ron was probably talking about. Since it was setup with
internal sync and to play from the static tempo map, it wasn't ready to
change tempo while it was playing. In this case, a tempo-sync'ed plug
could conveniently lookahead at the tempo changes to optimize
performance. The sync mode of the host is a fundamental mode that could
be queried by the plug.

Playing with a static tempo map is a common way to do things. e.g., Jack
and Jill setup some backing tracks and go to the bar and sing an play
guitar along with the tracks. The tracks play with a fixed tempo map, and
Jack and Jill follow along. Of course, what's they try out realtime
tempo-tracking from me or Koen, they might never use a static tempo map
again! :-)

In any case, I'm not saying tempo lookahead should necessarily be in
GMPI, I'm just trying to flesh it out.


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