[linux-audio-dev] XAP Time/Transport - varispeed/shuttle

David Olofson david at olofson.net
Wed Dec 18 19:12:01 UTC 2002


On Thursday 19 December 2002 00.55, Frank van de Pol wrote:
[...]
> > Of course, you may run backwards and stuff that way as well, but
> > don't expect the synths to play sounds backwards... ;-)
>
> yes, that is the idea. In fact some plugins would indeed play the
> sound backward (eg. scrubbing over a sample...), depends on the
> plugin :-)

It would work with hard disk recorders and the like, but synths and 
samplers (generally) don't play by musical time, so they wouldn't 
know where to start playing. You can tell when a note "starts" (by 
looking for control changes corresponding to "note off"), but you 
don't know when the note "end", unless you can read any events you 
like directly from the sequencer.


> this SPEED control allows the plugins to anticipate to the POSITION
> change events or discontinious position passed for the block to be
> processed. Fast forwarding without SPEED hint would result in fast
> skipping (like seeking on a mini disk deck); a slowdown would be
> euh, also result in repositioning, but nudging a bit back every
> block.

No, position changes are not just sent as absolute position, but also 
indirectly as "tempo". Since the tempo would be scaled as well, 
plugins would just think the tempo is different, and thus, beat sync 
effects, hard disk recorders and other musical time sync'ed or locked 
plugins will do the right thing.

However, your average sampler or synth will probably not timestretch 
to fit the tempo, so samples, envelopes and stuff won't track the 
speed control any more than they would tempo changes.


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

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