[LAD] 64 bit tempo-based time stamp

[David Robillard]

On Tue, 2012-02-07 at 19:29 +0100, Pedro Lopez-Cabanillas wrote:
> On Tuesday 07 February 2012, David Robillard wrote:
> > Hi all, seeking opinions:
> > 
> > I have to choose a way to represent beat-based tempo time in 64 bits.
> > Uses are many, but the main one is event time stamps for plugins.
> > 
> > Requirements:
> >  * No odd data sizes (for performance / programmer ease)
> >  * High precision (ideally close to sample accurate for most tempos)
> >  * Fits in the same space as two uint32_t's
> > 
> > Questions:
> >  * Is "bar" needed?
> 
> Probably not, for most use cases. Bars are required for notation, and useful 
> for rhythm matters, but the important rhythm element is the beat, and with 
> beat count and tracking time signature changes you can calculate the bar 
> numbers very easily.

True.  For some things you will need proper transport information
anyway, so perhaps it's not a good idea to complicate *everything* so
make the bar available, when no matter what certain things are going to
need to work with a real meter/tempo map anyway.

> > /* D (high range/precision, but no bar) */
> > double beat;
> 
> This would be my preferred option. It would be similar also to Apple's  
> AudioToolbox framework:
> 
> MusicTimeStamp. A timestamp for use by a music sequence.
> typedef Float64 MusicTimeStamp;

We use this internally for sequences in Ardour, as it happens.

> Working directly with beats (and 
> fractions) would be more natural for applications like 
> quantization/groove/humanization/swing, or other rhythm effects. 

This is true, and a very compelling argument, since this is the sort of
thing plugins are most likely to do.

Thanks,

-dr