ForumsDIY ← Alternative to that (expensive) 8-channel interface

So, I've got a PreSonus FireStudio that I don't mind devoting 4 channels to (some of the time), but I don't really want to devote all 8. Also, does it take 8x8, i/o or 8 in and 2 out? I'm asking because I want to do some distribution where I'd need just one input and four outputs, so I'm wondering if this could be like a complement to that.

One more question: if the 8 channels in are really, totally necessary, do you have any ideas of a good 8-channel cable-to-ADAT Lightpipe interface that I could use? What kind of preamps are necessary to get a good response? I don't want to spend the time making a lame instrument, but I also don't want to spend $1,000 on an 8-channel fancy mic preamp just to have it be basically useless.

All right, lots of text, but the basic question is whether the 8 inputs are totally necessary for this.

Oh, I saw that it was buried in the poly~. Sorry about that--I might try my hand at a 4x4, though. Has anyone else tried making one of these?


You can set up the controller in any kind of m x n configuration where you have m rows and n columns. Less than 8 will work fine, but the square grid approach will stop working as well when the squares are big. If you have only four or fewer steps on a particular axis, it will probably make sense to reshape the electrodes to use a tapered pattern, so that the voltage varies smoothly across a larger area. I've been meaning to write up more instructions on this approach.

Imagine that you have a long thin rectangle, divided into two long skinny triangles by a diagonal through it. Now induce an AC voltage in this strip at some point along it. If your two triangles are a and b, the position can be calculated as v(a) / v(a) + v(b). More info and a drawing are in the Radio Drum section in my Masters thesis.

I have tried out the MOTU Ultralite Mk. 3 and the RME Fireface interfaces. Both had pretty much identical performance. The MOTU is a bit trickier to set up the gain structure of, but it's $500 as opposed to $1200 or something.

Thanks for the reply. So, would FFT analysis allow the use of multiple triangle controllers on two channels? Or, even a single i/o audio channel--say you have 16 frequency bands, and the natural harmonics of a 512-sample sine wave (for perfect FFT analysis) and you just ran the same channel through all 16 triangles (8 pitches). Wouldn't you be able to split the signal apart using an FFT and judge the power of each individual band? I know that there would be a small frequency lag, but reducing the buffer size to 256 or 128 (or increasing sampling rate to 88.2kHz) would minimize the lag, albeit at the cost of CPU resources.

I'm particularly interested in the continuous-controller approach, primarily because my goal is to get Just Intonation on a much finer scale than any sort of existing MIDI controller. Also, I like how the reaction time is around a millisecond. Any sort of problems with too much skin of the finger touching aren't really an issue (any more than they are on the violin, anyway). Thanks again for your thoughts.

Hi A.C.--

Let me take a step back and explain the relationship between FFTs and audio channels.

There needs to be one audio channel---one sinewave carrier---per carrier antenna. These have to be on electrically separate surfaces. By placing a single pickup antenna near a combination of these carriers, the distance from the pickup to each carrier can be calculated from the combination of the carrier signals induced. The pickup would take a single audio input---it is this signal that is decoded by the FFT.

If you want to play around with this idea I would start by making a 1 by 2 setup, with two carriers and a pickup, and see what you can do. With two carriers as long triangles and one pickup over them, you would have a nice ribbon controller. I have been meaning to write this up as a DIY project for a while. I am still meaning to...