Mac OS X Con: Musical Interfaces

Saturday, November 6, 2004


Driving in San Francisco.

[Here are the details for this panel, fully titled “Physical Interfaces for Musical Performance.”]

Scott: I didn’t come up with a very catchy name, like the Powerbook Rockstar or something.

First we’re going to talk about physical interfaces. Real-world, hands-on. Then we’ll talk about virtual interfaces such as Ableton Live.

Why do we need a physical interface? I already have a keyboard and mouse, right? Some people prefer the erganomics of an external controller. [Holds up a white, plastic kid’s guitar toy.] Practicality is another good reason. Maybe you want to be something more of a rockstar.

Disadvantages to some of these are the steep learning curves sometimes. Rolling your own can be the most difficult. Off-the-shelf tend to be easier to use and configure. [He’s got an Evolution UC-33 control surface up on the screen.]

You can also take apart off-the-shelf tools and make your own with them. [Holds up guitar he made — same as above.] This has the guts of a USB keyboard. They keys are attached to the chord buttons on the guitar and he’s got a couple of knobs mounted on it.

[Showing some other devices he’s found that could be turned into an interface.]

I’m showing these because I’ve worked on them.

How do you get knobs onto you computer? Doepfer makes a CTM-64 MIDI interface component you could use to convert analogue voltages into MIDI data. Or data your computer can understand.

Sort of things you might want to interface with.

First, a switch. All of the guitar keys are switches. [Shows photo of guitar innards.] You can see the switches and the wires connected to them here. I opened up the body of guitar and wired everything to the neck. To the contacts in the neck. So when I press a button, the computer sees it as a keypress. If you use a USB board, your instrument could actually be a hub.

You’ve got to be prepared when you do this that you might fuck around and accidentally short something or fry something like hte USB port on your computer. And don’t spill things on the electronics. If you fry your USB port like this, Apple may not fix it…

Now — potentiometers. Can’t read a variable voltage with a USB hack. There are other hardware options, though.

Old ball mice use little disks with holes in them so a little light sensor sees different patterns of light through the holes depending on the direction of the turn. That’s what he did to ake the guitar knobs. is the electronics supplier from which I buy a lot of my stuff. [He moves the cursor around the screen by twirling the knobs on the guitar.]

What about getting voltage out of the device? The voltage comes in pulse waves (called a “duty cycle”). As you increase the duty cycle the receiving device kind of forgets the gaps and averages out the voltage. [Or something like that.] This happens hundreds of times per second and can be used to adjust brightness of LEDs or the speeds of motors and such. I used it to monitor the signal output of the device I build.

As far as performing with this stuff. The guitar is kind of still in progress and I’m afraid to pull it to far away from ther computer, but here’s a demo…

[Playing a glitchy little number using the guitar as a controller.]

I used Ableton via a Max/MSP patch to connect it to an external keypad.

This guitar was $3 at a local thrift store. Bought the bigger things from a guy who didn’t know what they did. Which is fine, because I gutted them, mostly. My parents also have some stuff. You don’t have to pay a lot for these things. It’s remarkable the amount of stuff that’s floating around. I’ve got bunches of stuff I just walked out of the university with and they didn’t care — they were glad to have me take it away. Duke University also had a surplus. None of them seem to care.

I built the guitar for this conference because it’s small and can be carried on the plane.

Wearable computing is a big buzzword, but there’s not reason it can’t be built into a gassmask or something. They’re cheap. I’ve got a gasmask with a little USB keyboard in it, has buttons around the edges. There’s really no end of fun if you’re willing to tear things apart — and the key, of course, is to get these things for free.

We were talking about aesthetics earlier. Playing with this guitar would have a certain aesthetic to it. Some drums I have lend themselves to palying more goofy, toy-like music.

[Now he’s showing the Max/MSP patch he uses to convert the MIDI to something Ableton Live can use.]

Names of some of the IO boards: makes some of them. Their stuff is very robust and durable. are good, also. Fusion Systems iCube is another MIDI box. EasyIO is a serial adaptor that’s available.

Commercial controllers are a bit more reliable. Invariably I’ll be playing somewhere and something will come unglued or unsoldered. These commercial things are designed to endure the rigors of playing live repeatedly. But with my controllers, I can develop an interface with a specific performance in mind.

Cook at Princeton has a COW controller.