[sdiy] MIDI Clock sync advice

Spiros Makris spirosmakris92 at gmail.com
Wed Mar 20 08:53:11 CET 2024

I was thinking about it and the teensy interval timer class has an inherent
limitation. When the period of the timer is changed the actual period is
not updated immediately. The current timer cycle ends before changing it's
frequency and starting again. I'm sure you can change this if you delve
deeper into the hardware and set them up yourself.
If you are measuring the input frequency and run a timer based on that
measurement, in the case of an abrupt change you will inevitably have to
drop out of phase when using the interval timer I described above; a clock
that arrives sooner will be registered correctly as the new frequency by
your detector but the new clock won't be output until the last cycle is
over, effectively throwing you out of sync.
A behaviour akin to the avr timers wherein you compare a timer with a value
and reset would output the next clock as soon as the next measurement is
in. You will miss some time but probably not enough to make it noticeable.
Without any additional syncing this is a cumulative error and further
changes and noise in the measurements should eventually add up.
Should you try to run the clock faster, say 48ppq, you will run into the
problem of outputting an out of time clock before being synced again. While
the second clock after the change will have the correct timing relative to
the first, the sync is messed up, and the amount is relative to the tempo
change. You can "hardsync" to get the two clocks back in phase, but to
bring the whole beat back in sync you will have to output a short burst of
clocks so that all sequencers are back on track.
In retrospect, I've never used step tempo changes when making electronic
music, but it is a very intriguing problem.

On Wed, Mar 20, 2024, 01:07 Adam (synthDIY) <synthdiy at adambaby.com> wrote:

> On 20 Mar 2024, at 6:19 am, Chromatest J. Pantsmaker <
> chromatest at chromatest.net> wrote:
> Ableton Link provides both Tempo and Phrasing, so it will always start
> your sequencer at the beginning of a bar of the master clock.
> I think there is a solid market for an Ableton Link to MIDI device, but
> nobody makes one yet.  The standalone hardware devices out there only take
> Ableton Link and output triggers/gates.
> This sounds interesting. I wasn't aware of this thing.
> Anyone joining has their start time delayed to the start of the next bar,
> right? Nice!
> Looks like anyone on the network can change the tempo at any time!! Oh
> dear..
> Sounds like it has a lot of potential for jazz!!
> In terms of jitter, I wonder how it stacks up against the Innerclock
> litmus test gallery?
> A
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