Latency compared to commercial solutions ?

You may know that latency for a DAC/ADC is more a function of the sample rate and frames/buffer size than the electronics it passes thru. 

For pi-Stomp, you can change the latency to be low as 1.3ms to 11ms or more depending on what you choose for your sample-rate and frame size.  The 1.3ms (96kHz/128 frames) will not likely perform well except for very small/simple pedalboards (3 plugins maybe).  I find that 96kHz/128=2.67ms is a better choice to support more plugins (6 to 8).  96kHz/256 or 48kHz/128=5.33ms is better for larger pedalboards or ones with lots of simulator (amp/cab models, pitch shift, etc.) plugins.

If you want to see actual pi-Stomp latency (which is generally very close to theoretical), I've posted that (with oscilloscope plots!) here: https://treefallsound.com/wiki/doku.php?id=performance_tests

Regarding how that compares with commercial devices.  I'm not certain of the number of frames that various devices use but I do know that Line6 HX stomp runs at 96kHz and I can't imagine it uses less than 128 frames.  In that case, it would have a theoretical latency of 2.67ms.  Mod Duo runs at 48kHz, so I'd expect it's latency to be 5.33ms.  Those are the main "competition" so I'd say pi-Stomp is in good company.  Personally, I don't really notice 5.3ms.  10.6ms I do.

Thanks for the kind words and interest, Craig.

To your questions...  Full size pi?  Guessing you mean the "B" models?  Those would require a bigger enclosure, and for what advantage?  Extra USB ports?  You certainly could though.  It works just fine.

Regarding XLR, you could feed your mic to an XLR preamp or direct-box then to the pi-Stomp.  XLR on-board the pi-Stomp would require an additional preamp - current one is unbalanced with unity gain.  Here's a XLR input module with almost all the bells and whistles: http://www.fabmodules.com/shop/index.php?route=product/product&path=60&product_id=53

it or something like it could be wired in place of one of the existing 1/4" TS jacks and should feed just fine into the unity buffer.  Phantom power would require a boost converter or additional supply.

Regarding more footswitches/knobs, sure, natural thing to want.  I went with 3 footswitches because you can always add more by connecting any midi-controller to the DIN midi or USB ports (demo of that: https://vimeo.com/477461214).  FWIW, I've started prototyping an extension box that would add at least 2 footswitches, maybe some knobs, and *maybe* a small display to show the mapping of each control.  Once I sell out of pi-Stomp bundles (20 or so more to go), I'll likely start on a smaller/cheaper version with reduced functionality, but still expandable via USB/MIDI.  If you would like to give suggestions on either project or collaborate, I'm all ears.  If you want to create your own pi-Stomp XL/XLR, I could likely help you there.  There's currently only one unused GPIO pin, but there are 4 unused Analog over SPI channels which could be used for pots, footswitches, etc.   Technically, you could use the pi-Stomp PCB as is, but you'd have to hack on some analog input wires.  More ideally, a new PCB rev with a new header could allow easy connection.

Thanks for your reply buddy!

My thoughts of using a full size pi was more to get the power and ram of a Pi4 board in there :-)

I love the idea of a smaller unit, maybe something simple with the main I/O, a single button and a screen, then the user is able to pair it with any combination of expansion boards to give them the necessary input.

I'd personally love to build a similar simple module with the Pi4 and it's 4 usb ports, then use perhaps two microcontroller powered expansion boards for the footswitches via usb.

Hey man, as you know already I think this is absolutely amazing. I will hopefully get a kit when I can afford to pick one up.

In the pics it looks like a model A+ - have you any plans of making them to fit the fill size pi?

Im also intrigued by your proof of concept too; I am a trombone player by trade, and would love to work on a version of this pedal with an XLR Input, to take my trombone mic.

If love to know more about how you worked through your concept model and try coming up with a bigger board with a few more buttons and that XLR in 😎