[sdiy] Midi CC update rate question

[ASSI]

Am Samstag, 7. Januar 2012, 13:09:31 schrieb Richie Burnett:
> If I am designing a product with 5 knobs capable of sending MIDI CC data
> when they are adjusted what is a sensible update rate for their
> transmission over MIDI?

That's a loaded question...

> For example, if only one control is continuously turned the product could
> theoretically transmit CC messages at an update rate of about 1562 per sec
> if running status was used!  Whilst this ludicrous rate would surely be
> nice and smooth it also takes up 100% of MIDI bandwidth meaning the
> messages would have to be dropped by a sequencer in order to merge in
> other data.

Not to mention it would likely crash some synths.  Most  synths that accept 
"continous" CC data provide some filtering to reduce steppiness, so past a 
certain CC rate would not produce a "nicer" result anyway.  This would be 
the optimum rate to send at, but that of course gets you back to the opening 
question...

[...]
> I don't know if I am being too pedantic about CC message rates as
> sequencers and merge boxes will obviously drop CCs if things get a bit
> tight.  I just want to make the right engineering decisions at this stage
> rather than have something come back to bite me on the backside further
> down the line.

I suspect that many merge boxes wouldn't deal with that situation correctly, 
i.e. they might drop _any_ CC data instead of making the data stream more 
sparse for each of the CC streams they receive.

In any case, if you would allow the user to chose a maximum rate, preferably 
indepently for the aggregate and per each individual CC, you'll be leagues 
ahead of most stuff that is on the market today.

> Finally, I noticed that none of the synths and controllers that I tested
> used running status to compress CC messages even though it was the only
> data currently being transmitted.  Is running status meant to be used by
> synths and controllers that generate CC data, or is it meant to be kept
> only as the "sequencer's secret weapon" to compress outward going MIDI
> streams when things get a bit tight?

I've wondered about this myself.  My conclusion is that either nobody 
bothered to implement it or (more likely) that using running status just 
breaks too many MIDI merge boxes and nobody cared to deal with the 
predictable support disaster that would produce.


Regards,
Achim.
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