Use of Octo with rPi's MIDI or separate MIDI device

[squidbidness]

I have a project in mind to build a custom multi-effects pedal for guitar, based on the Raspberry Pi 3 B; something quite similar to the Mod Duo. I've had my eye on the upcoming Pisound audio/midi board for the RPi, but I just discovered the Octo and it seems more particularly suited to my purpose (and less expensive). The multi-channel inputs and outputs are the particular draw, since then I could use these to give the pedal multiple effects loops, for example to send a signal with some effects already applied to my amp's pre-amp then back to the pedal (using the pre-amps effects loop), for more processing by the pedal before sending to the cabinet speaker.

My one hesitation before pulling the trigger and ordering an Octo is whether I'll be able to make it play well with MIDI. I plan to use MIDI to control looping software (such as Luppp, SooperLooper, etc) on the pedal, as well as to trigger/bypass individual stompbox emulators in the pedalboard simulator or to trigger scene changes, etc. I'm a novice in this area, but I've read some sources online that indicate that using more than one sound card can be a concern if the different cards use different internal clock rates -- that this can pose concerns for syncing the different cards without raising quality issues. I'm presuming that the same would apply as regards syncing the Octo's sound devices with another MIDI -- am I right in this regard? I realize this might not be such a concern for simple CC events such as 'play' commands; but it would be nice to keep the options open for use with actual MIDI instruments.

I wonder if someone more knowledgeable than I can shed more light on this, and offer any reasoning about whether such a setup should work well or not.

Thanks

-Andy

[flatmax]

I can try to help you, however MIDI isn't my forte

How is the MIDI going to interface the Pi ? ethernet or usb ? Or will it be external ?

Matt

[squidbidness]

The actual MIDI controller would likely be external to the Raspberry Pi (3 B, or maybe a Zero), driven by some version of Arduino, and connect to one of the Pi's USB ports. In other words, it would be an independent MIDI device that would send control signals (notes or CCs, probably) to the Pi. I'm presuming there would be a way to use both the MIDI device on the Pi's USB bus and the Audio Injector Octo in Jack simultaneously -- I've seen enough evidence of that kind of combination of devices being done in examples online. So I'm confident that this will be possible, I'm just trying to deduce if I will see clock drift issues between the external MIDI device and the Audio Injector.

According to this discussion, one of the major issues is MIDI over USB, period; Is it that the baud rate of USB just inherently mismatches that of true MIDI connectors? That's just my naive guess as to why, since I haven't fully grokked that discussion yet.

I'm also concerned about an issue from the Audio Injector and the Pi's USB bus introducing different latency values. I understand that there are various techniques to lower the latency of audio and MIDI through the Pi's USB bus, but still it's likely to be higher than through the Audio Injector, and it would be a pity to have to force the Audio Injector to a higher latency to match, if that's even possible or reliable.

I don't understand the issue fully yet, but hopefully my brainstorming here can give a better idea of what's concerning me.

[flatmax]

Regarding latency, I am not familiar with the MIDI USB protocol, however regarding audio the USB protocol tends to have largeish latency. Regarding clock drift, yes that may be a problem, however if you consider that you are playing an instrument in response to sound you hear, then clock drift may not be a problem ... as long as the recording system records everything relative to when it receives it !

I like your idea w.r.t. effects loops, sounds powerful !

Matt