ForumsHardware ← Call for input: Soundplane to CV module

This year it seems desirable and possible for Madrona Labs to make a Soundplane to CV device. This would be primarily a Eurorack module, but the circuit could also be built into its own enclosure for use with vintage synths etc.

Normally I do most of my design work in private, and only announce a product when it's pretty much done. But we (Brian and I) are going to change it up this time. Because neither of us is that deeply into the Eurorack world, it makes sense to solicit input early on in the process this time. This is going to be a utility device (though hopefully an elegant one) — so before we get too far along, let's make sure it will be useful to you!

The basic idea

USB jack for powering the Soundplane. Module puts out CV / gates / mod outputs for individual touches. Like the Soundplane app, a zone map decides how the Soundplane surface is divided up into notes and what those notes are. You can switch between zone maps, and the name of the current one should be displayed somehow. Aside from this, visual feedback will be at least an LED per Z value. To keep costs low, probably nothing too graphical or fancy.

We're looking for input on things like:

How many voices?

Each voice of touch output will probably have 4 outputs for pitch, x, y and z. Setting up many voices on a modular is not the way most people use them, so I'm guessing that two voices of output will take care of 90% of what people want. We would probably add an expander module for more voices.

Any interesting modes?

A switch that changes z (pressure) into a strict on/off gate might be useful. Any other things like this?


individual voice groups vertical or horizontal? voice outputs at bottom or top? I'm thinking top, because a USB jack on the bottom will go to the Soundplane.


The module will need roughly 250mA at 5v to power the Soundplane. Brian will correct me if I'm wrong. Then there's whatever computing and display the module needs to do, and the outputs. Do we need our own power supply, or a list of compatible Euro power supplies that we can point people to? Any choices in connectivity to make here?

Finally, we're still looking for a great name…

It's still in flux. I'd hate to tell you something and then end up having been wrong. I think we can safely say it will be less wide than it is high. (how many HP is a square anyway?)

Mockups come in at 8 HP for the basic module, 16 HP for the Chris Harris X special. Just an estimate for now, but that should give you an idea.

Ha! I'll make room for it whatever size it ends up being.

is it too early to ask for a rough idea about when this will become available?

It's not to early to ask, but it's too early to say! We still don't have final hardware, so it's more than just manufacturing delay at this point.

Any idea yet how deep is the module going to be?

We are not yet sure. It's a battle to make it skiff-friendly, but yet not overly wide, and we are still working out the details.

Is there a specification for how deep a skiff might be?
I did some research a while back, and came up with 40 mm. I also believe that I discovered that the "isms" modules are 41 mm deep.

Are there skiffs that are shallower than 40 mm?

I think shallower than 40mm (module depth) is very rare and people who have it probably knew about the limitations when they made it.

First prototypes, as shown at Superbooth in Berlin, are here!

I thought that folks who aren't in Germany would like a peek.

Soundplane-cv REV 2.0

This is most certainly a prototype. There are a number of details seen in the photo that will change. In fact, this particular face plate has a strange transform on the font that has already been fixed. Component positioning and screw types will be different on the shipping model. The number of LED indicators is planned to change, and my sloppy drilling that can be seen - if you look closely - will certainly not be part of production.

One of those ribbon cables you see behind the module is connected to a MIDI input/output board. This allows testing of the CV outputs independently of the Soundplane touch detection code. I have a simple voice allocation algorithm matched to the four-touch configuration shown, with Velocity, Pitch Bend and Pressure implemented. Paired up with a simple modular synth for testing purposes, everything seems to be working well, with 16-bit accuracy across ten octaves.

As Randy explains on the banner page blog entry, we really tried to pull all of the pieces together before Superbooth, but firmware is always the biggest challenge. We have vendor code for the USB peripheral, my firmware that's been growing as the platform has been built up, and Randy's touch detection that needs to be ported from a laptop computer environment (think: 1 GHz and huge memory) to an embedded environment (120 MHz, 256 KB SRAM). I am certain that we'll be able to get everything working, but at the moment it's MIDI only.


Great job guys!
Is the display here to stay or is it there temporarily to test things out?

It's gonna have a display. Top dial selects a parameter and then the bottom dial changes that parameter. Both changes are shown on the display.

Was really hoping for a "blind" panel, but I guess this opens up a lot of possibilities.
Looks like I'm gonna have to break my no-display rule for this one.

looks great, very excited! will it be possible to assign trigger out instead of gate? and maybe responsive to the pressure, eg a short trigger from 0-10 volts or something...that would be incredible!

This is such a fantastic news !

We have to get the touches working now and see what extra features make sense to implement. I hear that a selectable length trigger might be nice to have.

@timoka Moog S-trigger is not possible, as mentioned before, because it's a current function rather than voltage. Apart from S-trigger, some control over gate length would be nice. If you have example patches in mind that would require a fixed-length trigger, please share them here so we might try them out.

@rsdio ok, well i meant short spikes in the ms range, around 10ms is a good length to avoid the double triggering sound when pinging a filter.
here's an example of pinging filters with a piezo mic and a module which converts the piezo information into a trigger with variable dynamic voltages:
so this was my thought, having a trigger mode on the module with fixed length but variable voltage reacting to finger's a technique i use almost daily to excite sounds, either filters or physical modelling patches like rings or karplus strong setups or even something like the norddrum2 reacts dynamicly to variable voltage triggers. most trigger modules just spit out a fixed trigger and one has to use alot of vca's to have simple drum-like sounds behave dynamicly, a variable voltage trigger however would be so much easier for these kind of sounds and patches! here are more examples:
it's just triggers into filters near self oscillation but to be able to play this with the soundplane would be a dream!!

so to summarize my thought:
we could set the trigger or gate length in the menu (everything from 5ms triggers up to gates with sustain) AND a menu option where we could decide if it reacts to finger pressure or not.

By pressure I guess you mean note-on velocity? [edit] I guess if you don't mind a "pulse" that is not a constant amplitude you could map amplitude directly to pressure. Seems worth trying at least!

yes sorry, i meant note-on velocity!

it might be nice if Z could be switched between pressure and (note on)velocity

will the firmware be user upgradeable, handy if any bugs become apparent etc.
(and open sourced?!)

really looking forward to this, if you need early adopters/testers, Id love to help out.

(im definitely going to need more oscillators/filters and vcas :) )

velocity on gate is something that seems to be used in the modular world. so long as the gate is greater than the required 2 V or 3 V threshold it will suffice to turn on anything expecting a binary input, and then the exact voltage level would indicate strength via velocity for cv destinations that support it.

personally, i think that pressure may be the most important dimension, so it shouldn't get stuck at an initial value. in contrast, it's fine if the gate gets a steady value.

@timoka thanks for the examples and numbers. 10 ms is definitely within the realm of possibility. i read somewhere about gate/trigger pulses as narrow as 50 us, and that would certainly be challenging.

i'm not sure how fancy things will be at the start, but some way to set gate time and amplitude will certainly be prototyped. gate time could either track touch time, or be set to a fixed value, or perhaps be proportional to velocity. gate amplitude could either be fixed at something like 10 V or 5 V or be proportional to velocity, with a built-in minimum to keep modules happy.

@rsdio thanks, that sounds good!
if the gate/trigger length could be set within a certain range (let's say good for exciting signals, from 0.5 to 10 ms for example) and this range would vary proportional to velocity on note-on...this would lead to the most interesting timbres. i thought about it a bit longer and to be able to vary the length like this would be more useful since it leads to timbre variations PLUS amplitude variations where a fixed length trigger plus variable amplitude would only modulate the volume.

@rsdio , agreed, I tend to mostly use Z straight into a vca , so you can play the envelope.

And I don’t see that changing in eurorack :)

any news from this project?

We put on a big push for Superbooth, which was exciting. I'm working full time on Sumu (the next plugin) now. When Sumu ships I can return to work on the module.

any news on this? release at superbooth ? ... my rack is waiting for this now :)

lol - just noticed, first post on this was nearly 4 years ago... doesn't time fly!

I have to finish Sumu first. So, no release at Superbooth unfortunately. Time really does fly.