have you got some details .... id be interested to know...
(ive not heard/ seen evidence of any special pd interaction... its not in their GitHub repo, I'd assumed it was a standard alsa soundcard , since you don't have to use PD on organelle)
Ive been going thru the source code, and as far as I can tell its arch linux running on an arm 1ghz a9,512mb ram, single core (I was disappointed it wasn't dual) and uses an stm32f0 to interface to the oled/knobs etc but I cant find any information on the codec it uses.
I'm not saying its bad, even a PI that is setup well, can be a good audio processor (as I said, I've backed a pisound hat, ive also a HiFi berry ), but Ive not seen any claims its low latency platform (even from C&G ) - its designed as general purpose synth/fx box, which is cool enough....
the reason ive not bitten, is actually I don't like the keyboard, looks nice, but its clunky, and doesn't support velocity.
If you wish the difference is Axoloti and bela are designed to make instruments from (Organelle is already an instrument) so have to be low latency.
hard to compare...
bela is running linux (albeit real time, Xenomai) , whereas Axoloti has no overhead of a real OS
but the BBB has a 1ghz processor, so 5x more powerful. what I like about bela is it has 8 analog in and outs - and they are 5v tolerant (strictly 4v range).
if you need low latency (<1ms) and cpu grunt, bela is hard to beat, but its getting on 3 times the price (BBB + bela cape) of Axoloti , and more if you want the audio expander cape.
on the flip side, its lower level, so sure you can use SC/PD or C++ , but its not as easy as Axoloti to throw stuff together (hence my comments in this thread PD)
I guess i could run some benchmark tests, e.g. number of oscillators, filters, etc but wouldn't demonstrate much (as they wouldn't be exactly the same), but its also not that interesting (to me)
I look at these things differently... Axoloti and Bela (and the PI3 I have), i look at as projects, something I want to build an 'instruments' on top of, each provides potential to build something very unique/interesting/personal... (perhaps why i run cold on organelle, its a bit too finished in form/shape?), depending upon my ideas for the project, I'm might try to use Axoloti, or bela, or a pi3, whatever will do the job, I'm not really too worried which tech I use...
(which gets back on topic, using Pure Data vs Axoloti vs Supercollider vs C++... I'll use any, as long as i enjoy it )