[sdiy] MIDI clock query

[Colin f]

> I've just seen on the following page a claim that MIDI 
> includes two messages for timing "Clock" (&F8) and "Tick"(&F9).
> 
> http://en.wikipedia.org/wiki/MIDI_beat_clock
> 
> I've never heard of such a thing before (Only "Clock", never 
> "Tick") and other sources say &F9 is undefined. I can see the 
> point of having two messages - I'd always wondered how MIDI 
> indicated the start of a bar. But I doubt this is true.
> 
> Does anybody know about MIDI clock enough to fill me in?

The early drafts of the MIDI spec had a slightly different implementation of
clock.

F8 : TIMING CLOCK IN PLAY
F9 : MEASURE-END (transmitted instead of F8 at the end of each measure)
FA : START FROM FIRST MEASURE
FB : CONTINUE START
FC : TIMING CLOCK IN STOP

The idea of the 'stopped clock' was that devices with a higher resolution
through clock multiplication would be locked to the correct tempo before the
clock returned to running state.
In practice, you can just keep the F8 tick going, even while stopped.
F9 was dropped before any devices were produced, and FC just became STOP

Cheers,
Colin f