TL;DR: Digitone with external clock sync over USB has serious jitter? See examples
When my Digitone is slaved to external clock sync over USB, it has some serious jitter issues, which are particularly noticeable when using the onboard delay send effect. The delay lines are pitched out of tune by the variation in speed. This is maybe not suprising given the nature of my setup, which is not ideal in terms of avoiding jitter.
My master clock is the Octatrack, which sends clock to various MIDI destinations, including my audio interface. Some of my gear recieves clock directly via MIDI DIN, and other gear are synced over USB MIDI via the computer. The convertion through the audio interface to the computer, and back out again surely introduces some amount of jitter (and whatever round trip latency 64 samples at 48K produces, but I don’t think that’s relevant here).
This results in the before mentioned nasty out of tune delay lines. There are probably other unwanted effects as well, but to my not so fine tuned ear, it’s not really an issue. If there is some off timing, I’m happy to call it “swing”. The delay lines are however disharmoneous, and renders the delay effect unusable in this scenario.
The strange thing is, however, that the delay lines produced by my Eventide H9 pedal, which is also synced to the same source, over USB via the computer, does not have this issue. It seems to be, well, not dead stable, but at least usable to my ears. There really isn’t the same amount of crazy out of tune stuff as on the Digitone. The Digitone and the H9 are both connected to the same USB bus on my computer, both to two adjacent USB2 ports at the rear.
So this leads me to the question: is this due to differences in MIDI implementation on the two devices? Or perhaps in hardware or DSP? Is there perhaps a point in troubleshooting using different cables, switching to USB3 ports, etc?
Attaching two examples, where a chord stab is sent to either the internal delay, or the external H9 delay:
Internal delay:
External delay: