[sdiy] Bunching of MIDI clock messages

Tom Wiltshire tom at electricdruid.net
Wed Sep 11 21:23:36 CEST 2013


That's how I did it. Seemed reasonable to me. I would imagine other people have had the same idea as us both. I have to admit that partly my motivation was to avoid repetitive MIDI clock and other real-time data clogging up the MIDI input buffer, rather than any high-minded sense of timing accuracy!

Tom

On 11 Sep 2013, at 13:39, ChristianH <chris at chrismusic.de> wrote:

> 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.
> 
> Chris
> 
> 
> 
> 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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