Friday, June 4, 2010

Updated Trombone Controller

Over the past month or two, I've been slowly working on a refinement to the trombone controller, and I've finally got something that's physically stable and reasonably playable. Here's an update:

First, here's a photo of the prototype:

If the wooden handle (used to hold the instrument) looks like an axe handle to you... you'd be right. I'm still working on how the performer's left hand is involved, but for the time being, I've relegated it to a supporting role.

The major change between this prototype and the previous prototypes is the slide. The new prototype is essentially a copy of one half of Thomas Henriques Double Slide Controller. The basic construction is pretty simple, and involves:

  • A piece of 1/8" x 1 1/2" x 36" aluminum stock (Home Depot) - the substrate for the "trombone slide"
  • A 24" x 2" piece of plexiglass (Tap Plastics - a 15 minute walk from my house) - the bearing surfaces of the "slide"
  • A 5" x 3" piece of plexiglass, that holds:
  • Two 3/4" x 2 3/4" blocks of teflon, which I shaped with a router, and ride along the long plexiglass piece. These are equivalent to the outer parts of the "slide"
  • A repurposed joystick controller, which the player holds in his/her right hand. The controller handle is used to move the "slide", but also has 5 buttons that control overtone selection and a slide quantization mode (I'll explain that later). The buttons were epoxied into holes drilled into the joystick handle.
  • A project box that contains a Freescale pressure sensor, and all the wiring interconnects.
  • A "mouthpiece" that allows the performer to blow into the pressure sensor.
To set the stage, here's a little video that shows how the instrument is held, and how the slide moves:



There are three types of sensors on the instrument:

Breath is detected via a Freescale pressure sensor. In the photo below, the mouthpiece (the clear plastic vinyl tubing that the player blows into) is connected to a box with some 1/4" tubing. The box contains the pressure sensor, along with the other wiring interconnects. At the top of the mouthpiece, there is a "T" connector that allows half of the airflow to exit (so the player feels like s/he is blowing through the instrument) and the rest goes to the pressure sensor. The Arduino code reads the sensor and produces MIDI Breath Controller data.

Slide Position is detected with a SpectraSymbol 500mm SoftPot linear potentiometer. The SoftPot is adhered to the aluminum stock using the adhesive backing provided with the SoftPot. The aluminum stock is screwed to a slightly wider piece of plexiglass. A mechanism slides along the edges of the plexiglass. The bearing surfaces are made of teflon block. I cut a groove in two pieces of the block using a router, and these grooves line up with and ride along the plexiglass, as shown below.

In the middle of the clear block, you can see what appears to be a setscrew. This is actually a stylus that is manufactured by SpectraSymbol. You can't see it in the photo, but the end of the screw is a small nylon stylus that rides on a small spring that provides a constant force. This makes the pressure on the SoftPot very consistent, which means the slide behavior is very predictable.

The Arduino code reads the slide position and computes the appropriate pitch bend to send. My most recent firmware also includes a mode where the slide positions are quantized - in effect, the slide "clicks into position" automatically. Although a glissando isn't possible with this setup, the instrument's notes are always in tune. The slide quantization mode can be toggled on and off using the thumb of the right hand (there was a spare button on the joystick handle that was perfect for that).

A future enhancement I'm considering is providing an LED on the instrument that lights up when the player has the slide in one of the seven positions (well, actually, within a certain range of the dead-on position). Trombonists are used to reaching out to touch the bell to gauge where 3rd position is; this LED would do the same thing, but for all seven positions.

Overtone Selection is accomplished via a set of four switches on the handle that the player uses to move the slide. Here's a picture of the handle:

The handle is a repurposed joystick, with some momentary switches epoxied into some (very crudely drilled) holes I made in the handle. The "trigger" button is actuated with the index finger, and the remaining buttons are operated with the second, third, and fourth fingers. By using a simple "chording" method, the player can select any one of eight overtones:

Overtone 0: off off off off
Overtone 1: on off off off

Overtone 2: on on off off
Overtone 3: on on on off
Overtone 4: on on on on
Overtone 5: off on on on
Overtone 6: off off on on
Overtone 7: off off off on

Now, only 8 overtones is not really enough to make a trombone player feel at home (most accomplished players can produce at least 10), so I need to think about this some more, but 8 overtones does give me enough range to play stuff that's interesting.

Here's a short video of me playing a little improvisation on the instrument. I still have some work ahead of me to produce a patch that makes the instrument play well. The patch you're hearing is one I built for the ES2 FM synth that comes with Apple Logic Express.


I have to say that, while the instrument is still pretty glitchy, I'm starting to feel like it's possible to be expressive with it. I'm also feeling like the instrument is pretty consistent; it behaves predictably, which allows me to practice a musical passage, get it right, and then to be able to perform it in a repeatable fashion.

Finally, as a point of comparison addressing the expressiveness of the instrument, here's an improvisation in the same vein, but on my trombone.