[sdiy] Bunching of MIDI clock messages

ChristianH chris at chrismusic.de
Wed Sep 11 14:39:24 CEST 2013

Wouldn't it be more reasonable to immediately increment some internal
time code counter right from the MIDI reception interrupt handler,
rather than checking for it at some other time after passing through a
FIFO? Isn't that what real-time messages are about?
Ok, probably some locking mechanism will be needed to prevent
concurrency issues.


On Wed, 11 Sep 2013 12:32:31 +0100 rburnett at richieburnett.co.uk wrote:

> How common is "bunching up" of MIDI clock messages due to erratic 
> transmission out of sequencers?
> For example, if I check for the reception of a MIDI clock message every 
> 2 millisconds in a receiving instrument is that sufficient?  (In theory 
> 2ms polling rate should be sufficient to support tempo up to 1250 BPM 
> provided the clock events arrive with even spacing!)  Or do you think I 
> should cater for the possibility of receiving as many as seven MIDI 
> clock events transmitted "nut to butt" over my 2 millisecond polling 
> period!?!?
> I know the MIDI specifications says that MIDI clock messages are to be 
> transmitted with even spacing at the average tempo rate, but I don't 
> think i've ever seen a maximum jitter specification anywhere?  (I can 
> just imagine sequencer software getting preempted in a Windows 
> environment, and later transmitting all of the overdue MIDI data in an 
> intense burst.)
> Any thoughts/experience on this?
> Cheers,
> -Richie,
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