Hello everyone! I am in the process of building my 1st eurorack with biofeedback from plants and humans. It will consist of atmospheric, pscychedelic, grooves from plants, sensors and various outboard gear. This first stage is mostly for ambience with various percussive rhythms and building up to have a plant band.

I currently own a Structure 208hp case by Pittsburgh Modular, 2 Instru Scions, MI Rings, Strymon Magneto and Roland 531. And also have a 2.4sink for more biofeedback on order.

The pieces I picked out for the eurorack are close to what I could imagine it doing but would greatly be appreciated for more input and discussion on this rack, patching, links, and future ideas.

Thank you, SvenZ


I like the idea!

Unfortunately, unless I am missing something, you don't have enough CV utilities for attenuating, inverting and mixing your CV signals. Maths, sure, all well and good, but for the number of modulation sources in there I would say you need at least a couple of extra CV processing modules - say something like MI Blinds.

You're almost certainly going to become very frustrated very quickly without these!

If this doesn't make sense to you and you don't understand why you absolutely need these kinds of utilities, please say so and I am sure someone, possibly myself, will point you in the right direction :)

I am taking commissions for synth builds. UK ONLY for now. DM for details :)

You can find my modular synth album here https://kel-audio.bandcamp.com - enjoy!

Thank you Kel, this is the feedback I’m looking for. I was trying to squeeze a quad VCA into the rack but can see I can do a bit more with MI Blinds. If you needed to adjust the rack to fit it in, what might you do?

Um, this is work... need to think about it! Give me a day or so ;)

I am taking commissions for synth builds. UK ONLY for now. DM for details :)

You can find my modular synth album here https://kel-audio.bandcamp.com - enjoy!

Conceptually, this is interesting, but I'm not sure exactly what this cab is for. Is this a "voice", or is this where you intend to do the signal conversion?

One other point about biosignal work: it's not merely a matter of "connect ficus tree to input preamp". In order to amplify signals of this magnitude, you'll probably wind up needing far more gain than a typical Eurorack input can offer, plus a good bit of signal cleanup. For a decent older example, see l80AAOSwJU5drCq6" target="_blank">https://www.ebay.com/itm/EEG-POLYGRAPH-DATA-RECORDING-MACHINE-GRASS-MODEL-79D-PARTING-OUT/153691498905?hash=item23c8ba2999l80AAOSwJU5drCq6 What you choose for electrodes and leads will also be important; some work well for one application, but are utterly useless for others.

You'll mainly be looking at EEG gear for your signal pickup, since those systems have the necessary amplification factors to bring the biosignals up to a relatively usable level. They also tend to offer the HP/LPFs needed to remove noise and spurious signals on the input...and believe me, you WILL be wrestling with that noise/garbage issue, since it only takes a few feet of unshielded cable to pick up enough electronic crap at the required amplification levels to render all of your bioinput totally useless. However, if you're uncomfortable with electronics that go WAY outside typical synth gear...well, you're just plain screwed. This is very much one of these control methods that requires going outside of most synth users' comfort zones.

It's an interesting idea...one I've tinkered with on occasion. But at the same time, it's an infinite rabbit-hole...so be forewarned!

Hello Lugia and thank you for the wonderful feedback. I totally agree on a lot of what you say but am lucky to find ways around some of the problems you described.

Two of the modules I have do the converting of biometric feedback into CVs using electrodes and small clips. I am looking to expand upon this idea with more inputs from more sensors. The setup I have can do simple voicings, so one of the things I’m working on is the guts of the eurorack to create more complex harmonies, rhythms and algorithms.

I really dig the link you sent, hopefully my case ends up a bit smaller and lighter in the end.

Just remember: even if those Eurorack modules can handle the amplification level, you'll still need to extract your desired signal from what'll be a lot of noise. The two solutions for this are either very aggressive bandpass filtering after the preamp to localize the range in which the signals can be found (usually subaudio ranges) or the use of a lock-in amplifier which can "track" the signal as it fluctuates. I'd also suggest making use of several window comparators which can extract voltage level information and convert this into gates, which can then be used as needed.

And yeah, that Grass device I linked to is pretty chunky...but you have to admit that, as unwieldy as it is, that damn thing looks COOL in addition to being one (of several) of the right devices for the task. Not as technologically badass as MY lock-in analyzer (made by EG&G...the folks who also run Area 51!) that's on top of a rack right behind me as I type this, but those Grass things definitely have that "evil guvment lab" look DOWN. Test gear suuuUUUUUcks to haul around...but onstage, it definitely projects a "whoa..." factor!

Good things to ponder about and cool things to look at to keep the mind wandering. Thank you again Lugia!