P2 Eurorack SIG
Twyyx
Posts: 66
in Propeller 2
This thread is meant to be an anchor for P2 early adopters and developers who are building for eurorack modules.
Consider it a P2+modular synthesis special interest group.
I have started doing some R&D on building a set of euro-rack modules with the Propeller 2, but I'm still at the beginning.
I'd like to share ideas and compare notes with others who are willing to share their work in a public space.
Consider it a P2+modular synthesis special interest group.
I have started doing some R&D on building a set of euro-rack modules with the Propeller 2, but I'm still at the beginning.
I'd like to share ideas and compare notes with others who are willing to share their work in a public space.
Comments
I'd really like to understand how people use this eurorack gear to make cool soundscapes
I've got some hardware ideas to bounce too
I'm interested in finding the middle 80% of a common reference design (with help) and sharing that here.
I'm also interested in building a reconfigurable modular device which allows users to build and share their own algorithms and tools easily with others.
These are more long-term goals. My shorter term goals are to actually build some modules and experiments as stepping stones to get there.
Here are some interesting musing (not mine) on bit depth and sample rate for various signals:
https://euphonia.us/the-digital-representation-of-analog-synth-signals/
Also, the main "spec" for what we now call eurorack is here: http://www.doepfer.de/a100e.htm
There are variations on this theme, but this is spring from which modern eurorack designs flow.
Too bad that I have ZERO time to spend on yet another project. Being a family father with two small children takes almost all my off work time. It's a blessing and a chore at the same time!
For background, Pd (https://puredata.info/) is a software playground that allows one to construct a network of signal manipulation nodes visually.
While this environment normally runs on PCs, there's a C-based library (https://github.com/libpd/libpd) that can render the "patches" created with Pd to a callback that takes care of sending the data stream to audio hardware.
Not sure what the best application of P2 to Pd might be, but wanted to expose y'all to it for discussion.
-joe
@octetta I don't think you're hijacking anything. Interfacing is one of the most important and hardest challenges for us to deal with here.
It is interesting to imagine a pure data patch being rendered into a native P2 form. I don't think this can easily be done as a cross-compiler tool at the instruction set level, but I do think there is a way to map the libraries and processing graph in puredata to an equivalent set of modules and routings within a P2. Simple oscillators are just LUTs or waveform generators or system counter tricks.
But there is a missing piece that I think we would need in general to mix P2 audio designs with PC elements in real-time: A DAW interface for P2. It is easy enough to hook an analog device to an analog IO on the P2, but this gets clunky, more expensive, and more limiting than something that could speak waveform data directly to a P2 audio component. I wonder if anybody has already done any work on this. If not, it seems like @Ahle2 's work on reSound is perfect to be joined with a low-latency interface board and desktop audio driver. (ASIO or similar)
I wish I had more time to work on these projects too. When the tide shifts I'll have a few days here and there to jump in and get my hands dirty.
I've done some experimentation with display forms that would be useful for configuring a eurorack modular component.
The first was the 64x64 LED panel. I really like this one, and it is exactly the right size to fit on a eurorack system, but it comes with some trade-offs: 10W power draw is significant. Perhaps 3-5 times the power draw of a typical module.
Also, it is only a display interface. Without some type of tactile overlay, it's just a visual. It would almost certainly need to be paired with a capacitive overlay, or additional panel space for a dedicated set of knobs and controls.
Yet, the visual appeal of a crisp and very responsive display is undeniable. It's more fun to look at than the little LCD and OLED screens found in many modules.
The second is an import version of the 320x240 TFT LCD Panel. I really like these, but programming them is a bit of a nuisance due to all the TFT-specific settings you have to account for. Still, with PASM, I was able to get these to refresh at very high rates. (I had to add NOP instructions in a couple places to ensure reliable latching over SPI).
These panels have poor off-axis visibility, but at least they come with a resistive touch interface. The fact that they come with their own internal display RAM is handy, meaning you can use immediate mode rendering as long as your application state doesn't depend on pixel blending or related functions.
After implementing a partial driver for this display, I realized that @Cluso99 already built a full driver for the larger panel size. Reading that code was really helpful in thinking about how to build a dedicated immediate mode driver for the smaller format. (Thanks @Cluso99 !)
Next on the "try out" list is an OLED module. I have several formats of this laying around. I really think this is going to be the primary configuration interface. The power envelope is good, the clarity is good, and they can be found in many different sizes.
Why all the talk on display modules when this is a eurorack thread? It's because I want to be able to interactively configure and experiment with different algorithms. If possible it would be really awesome to be able to hit an authenticated website from within the interface to download DSP routines. Also, you would need to have parameter names and other details on the display to configure MIDI 2.0 signals.
Once the display is selected for this project, I'll begin testing the OpAmps and ADCs that are waiting their turn.
I haven't settled on the P2 package that I want to use. For building in bulk, a custom PCB makes the most sense, but for initial efforts it will be either a P2 Edge or a P2D2 or something similar. The P2 Edge Breadboard is the favorite way to prototype so far. In any case, I think it makes sense to standardize on the 8+8 pin grouping that the Parallax kits provide so that people can prototype pluggable components with a breadboard or a "module" in any form of completion.
ADC/DAC:
I did some research yesterday to try to source the AK* ADCs that we discussed on the forum. I found the original manufacturer's page, but no stock or mention of them at digikey or mouser.
For now, I'm going to stick to some of the ADCs and DACs that are carried in bulk supply at mouser with simple bitstream interfaces. These are, as Chip said, pretty affordable to use in designs.
Displays:
In terms of display, I've settled on using OLED displays, with the larger LED panels being used as accessories at some point.
Inputs:
The "big wheel" input based on the high precision rotary encoder and the hefty aluminum jog wheel is coming along. The machining is partly done. This will come back to life after this week when I'm on break.