Just tried to MIDI sync an external device with Polypulse MIDI clock OUT and apparently output BPM is not accurate.
For a BPM of 113 inside Polypulse track I get 226 BPM at its output → outgonig to my external device.
While using my DAW MIDI clock OUT I get no BPM issue at all with the same external device.
Update:
The issue was due to the fact I was using “Midi clock out” and "“MIDI in to out” parameters (in settings menu) activated at the same time using external MIDI clock in Polypulse MIDI in port.
So this two modes were adding up clock twice which resulted in a 226 BPM at the Polyulse MIDI out port.
BUT !!!
How I got to that point ?
It’s because I noticed Polypulse can’t handle “MIDI clock in” very accuratetly (at least for now), so I did some workflow test. The result is Polypulse fluctuates a lot from receiving MIDI clock in which make it very unpredictable to use (record it) when synced.
It fluctuates by about ± 4 to 7 BPM sometimes (meaning for a middle 113 BPM setting It randomly fluctuates from 109 to 120 BPM trying to sync with external MIDI clock), which is a lot.
For information Polypulse is reaching about 81% total cpu in my session.
BPM fluctuations should not be so high using external MIDI clock in.
I have another sampler using the same external MIDI clock at its MIDI input and fluctuations are in a window of about ± 0.2 BPM max.
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Update:
It looks the reason behind that BPM MIDI clock in fluctuations is related to total voices polyphony used and cpu managment.
My session is peaking (a few times) at about 14 to 16 total voices of polyphony (but it looks it’s really at 16 total voices of polyphony the problem is triggered) with a total cpu at about 81% that’s exactly at this moment issue is happening.
So It seems my Polypulse session is reaching the system limit.
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Just for information, I only used audio samples for that Polypulse session.
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Ah that explains it, thanks for letting me know!
When more CPU is used for generating audio there is less time for background process such as rendering graphics for the display and MIDI I/O. This means that if the CPU reaches above ~80% the display will update less often, but also there is less time for the code that receives/sends MIDI. So what you have noticed is correct.
The PolyPulse uses algorithms to improve unstable MIDI clocks and reduce clock jitter. When the machine is at 80+% CPU however it becomes very hard however to correctly estimate the incoming BPM.
Some manufacturers hide jitter in MIDI by simply not showing the decimals of the calculated incoming BPM or only updating the BPM number the user sees every once in a while.
A possible solution is instead to sync the PolyPulse using the clock in and pulse jack located on track 1. These are sampled at audio rate and do not get unstable in high CPU projects.
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Ok, I’ll try that !
Thank you for your informative reply Ward.
Best
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