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Audio Sync Specification

Posted: 06 May 2023, 23:13
by mineral

What is the exact specification of the sync pulses?

- pulse length
- shape
- amplitude
- timing
- quantity
- distribution

For both, the low pulses and the high pulses as well.
And of course any other important detail would come handy.

I am looking for a useful, tempo following solution. I tried to make something myself but due to missing details I could not make it work.

Many thanks!


Re: Audio Sync Specification

Posted: 07 May 2023, 19:50
by Simon
Hi :)

I suggest you use the Sync File Generator, generate a simple 2 bar file and have a look - that will gives most of the info you need ;)

To complete that (these are not exact specs - it's just on the top of head but it should help you getting what you need):
* the sync is based on 24ppq pulses, min 0.3V, max 0.9V
* rising edge is the one that matters (= the one used for the sync)
* pulses must be short, say min 0.01ms, and max 2ms
* to know where the bar is, there is an extra high pulse (min 0.9V) shortly after the last pulse of the bar, ideally right after like on the files generated by the sync file generator.

That high pulse is *not* used for sync and does not need to be precise, it's a bit like a reset to tell the Midronome "next pulse is a new bar".

Hope that helps :)


Re: Audio Sync Specification

Posted: 08 May 2023, 22:15
by mineral
Hello Simon

Thanks for the explanation, but somehow I struggle to understand when does it work and when it doesn't.
Could you please check the 2 sync files in the attached .zip for me and tell me what is wrong with one?
With one file it just displays Err or doesn't give a steady tempo.

Is it the pulse form, the amplitude difference, the timing?
How does it need to be different to get it work?

Many thanks!

Re: Audio Sync Specification

Posted: 19 May 2023, 22:19
by mineral
Any input?

Re: Audio Sync Specification

Posted: 21 May 2023, 17:17
by Simon
mineral wrote: 19 May 2023, 22:19Any input?
Sorry I must have missed your post somehow. I checked the files and imported them both in Studio One.
They both work for me, the "does_not_work" one is not exactly at 120bpm though, more like 119.5bpm, so the display on the device is constantly changing between 119 and 120. It looks ugly (and would not if the tempo decimals feature is implemented - but that's outside of this discussion) but does not affect the sync: the device syncs perfectly fine and your MIDI clocks run at 119.5 (or whatever the BPM of that file is).

A few points to note:
  • Your "does_not_work" file is a lot louder than the other one - I had to change its volume. When you make a new file make sure to go back to the settings, in inP then Syn and adjust the volume till you are in the "middle" of the green zone (as explained in the manual)
  • Make sure the "high" pulse is about 6dB to 10dB higher than the tick pulses (the tool uses 8.67dB)
  • The "high" pulse cannot be more than about 2ms later than the last tick pulse of the bar
  • It's up to you whether you want straight up square wave or (triangular) slopes. square signals are more precise but generate more ringing noise which can create issues
    (hence what the Sync File Gen tool generates: ticks rising edge with a sharp square for precision and triangular slopes everywhere else)
Hope that clarifies things and gets you going!