Hi! Glad to see excitement around this!!
I’ll try to address everyone’s replies - please excuse me if I forget anything.
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The latency is very low but I have not measured it yet. The only test I’ve done is play the output from my thing mixed together with the Digitone output, and I can barely hear any difference when I add combine the two. I’m sure there’s some latency, but it appears to be very small based on this not very scientific method. I believe if the latency was higher I would hear some kind of flanger/phasing/delay effect.
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I don’t expect any support from Elektron, so unfortunately future firmware upgrades could break this until adjustments to my code are made. I doubt that would actually happen, but you never know. My hope is that at least Elektron are okay with this kind of DIY work and that it is not a thing they would actively pursue to terminate.
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In terms of how I did it: The first step was to look for other projects doing this, at which point I found OB for Linux (sorta ;) which was extremely useful. I have a good amount of experience with circuit board design and the microcontroller l used. Once I decided to move forward with this I ordered an evaluation kit, a USB analyzer (a device that lets you inspect USB traffic between a host and a device) and began writing the proof of concept software implementation. Once I got that working I moved into designing the circuit board, and sent that to fabrication and assembly.
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I am planning on open-sourcing both software and hardware once I manage to find the time to clean and document everything.
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With regards to getting audio out of a Digitakt - my understanding is that this would let you get 8 mono channels out of the Digitakt (one for each of the 8 parts), as well as 2 stereo channels - the master/fx and the external analog input. I don’t have a Digitakt so I am unable to test it.
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The DACs that I used are PCM1681 8 channel DACs. I needed a total of 12 analog outputs (4 synthesizer stereo pairs + master/fx + external input). The microcontroller is an ST Cortex M7 (STM32F733)
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I am contemplating selling a pre-assembled kit - either the circuit board as shown in the photo, or the circuit board and a matching enclosure. I would try and do that if there is enough demand since supporting users comes at a non-negligible cost, even though I do expect this to be mostly a plug-and-play experience since there’s no software to configure and the set of hardware it interfaces with is very limited (currently only Digitone and Digitakt once I get a Digitakt to play with). Since I won’t be benefitting from economy of scale manufacturing just a few units, I expect the price to be around $350 for a complete kit. How do you all feel about that? I wish I could get it done cheaper but for an initial batch I don’t think that would be possible.
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One thing that I haven’t mentioned so far is that this is USB powered, which means you could easily power it with a portable USB battery pack. Unfortunately (but it makes sense that that’s the case) the Digitone/Digitakt do not output power over their USB port.
Thank you for your interest! Happy to answer any other questions, and if there is interest in a group purchase of this then I can look into how to get that done.