Sean Bratnober, John Nolting, Brook Reeder -

MUS 250a Fall 2006 - Final Project

CCRMA, Music Dept, Stanford University


Click here to see the process of constructing Myrtle
"Myrtle" - musical interface/controller

Myrtle is a music controller that communicates with a computer via OSC (Open Sound Control, an open-ended machine communication protocol) and MIDI simultaneously. The interface is primarily designed for controlling the pitch, amplitude envelope, and rhythm of three sound sources in real-time. Designed in conjunction with the PD environment, Myrtle currently controls a bank of FM synthesis objects via OSC, and can transmit 12 different user selectable MIDI notes via a standard MIDI out port. These notes are triggered real-time using the Penny and Giles fader.


Myrtle was designed to be used in a live-performance environment, played solo or as part of an ensemble. Instead of an "all-in-one" design, the functions of Myrtle are fairly specific, giving it a unique sound and feel. However, since it is only a controller and not a stand-alone instrument, it can be mapped to any number of different sounds or devices, limited only by the numerical data it puts out. The typical usage of the controller is with the left hand controlling pitch via the foam strips (see below), and the right hand manipulating the various controls on the right side.. There are many ways to use the controller differently than this, however.


Myrtle's construction took place during the fall of 2006 at Stanford university, as a team project. The goal was to create a new and unique tool for musical expression, and integrated into that goal was the idea that Myrtle would have the ability to control audio synthesis in complicated ways, using an intuitive and easy-to-use design. The combination of 3 different controls - a fader, optical sensors, and a series of buttons, used in conjunction with one another , were all integral in achieving this goal


On the left hand side are three 12-inch strips of fabric-coated foam rubber (mousepad material) are embedded into the wooden top, at a distance that is conducive to one-handed control.

On the underside of each strip is a length of magnetic tape. When the strip is pressed, the tape makes contact with a strip of grounded copper. By running a current through the tape, you can vary the output voltage by pressing at different locations along the strip. This information has been mapped to pitch, typically and octave range, so by moving a finger along each strip, the player can quite easily make an interesting polyphonic sound. Since the mapping arbitrary, each strip can have a different range and instrument that it controls.
In addition, a series of buttons just to the right of the strips offers additional control. Specifically, there are buttons to transpose the pitch up and down to increase the range of each strip. When the player lifts their finger from the strip, the voltage returns to zero and thus the sound will stop. By including a button to hold the pitch on indefinitely, the player can play pitches without having to constantly touch the controller. The hold button has an LED light indicating it's state
Creating pitches is only part of the controllers function. The right half of the device consists of various controls that extend the use of the device from a simple synthesizer into a versatile instrument:


A Penny and Giles (P&G) PGFX3412 fader controls acts as a switch, sending a signal to the computer to cut the sound or allow it to pass. This glorified mute switch extends the device by allowing the player to manipulate the sound rhythmically in the same way a turntable can be quickly cut in and out.

MIDI knob:

MIDI interface is accomplished through a Flesh O.N.E. A8_MIDI_V1 board. A 12-position knob works in conjunction with the fader to send out MIDI signals that act as triggers. The player can set which trigger they want to send with the knob, and then send it by sliding the fader entirely to the right. When the fader reaches it's maximum position, the trigger is sent. This combination is very useful for starting and stopping samples and other routines at a specific time, because it is integrated completely into the rhythmic part of the controller.

Effects Knobs:

Two knobs send out data from 0-1023 that can be mapped to any parameter the player wants to control live. Since Myrtle works in conjunction with an FM synthesis program, a handy use for one of the knobs is to control the modulation index of the synthesis, much like an analog synthesizer does (although everything is digital, and the synthesis done in software with Myrtle).

Optical Sensors:

The optical sensors, one of the more unique aspects of the Myrtle controller, are Sharp GP2D12 IR Sensors. When the fader is moved to the far RIGHT, the sound is cut off by a mute signal. When this happens, a mode is changed and volume can be controlled by triggering the optical sensors.  As it is currently configured, when the optical sensors are triggered, a message is sent that triggers an ADSR (attack, decay, sustain, release) envelope for the synthesized sounds. For more information on amplitude enveloping, click here.


The sensors and controls of Myrtle are all wired to an Atmel AVRminiv4.0 Buddha Board, which sends the control data via USB to a computer. The entire process is optimized for the linux environment, but OSC works under the Mac OSX environment as well.

MIDI board:

A separate MIDI processing board: Flesh O.N.E. A8_MIDI_V1.

Example Configuration:

here is a schematic laying out the lines of communication from the controller to the computer. There are multiple ways in which Myrtle can be used, this is the current configuration that works well:


as mentioned earlier, Myrtle sends data through the AVR microcontroller to a computer, which then routes than information into PD for real-time control over audio synthesis. PD is a graphical programming environment that specializes in audio. To see what the program does and how it looks, please visit this page: FM synthesis in PD

Internal Gear:

1x Atmel AVRminiv4.0 Buddha Board

1x Flesh O.N.E. A8_MIDI_V1 board

2x Sharp GP2D12 IR Sensors

1x Penny and Giles (P&G) PGFX3412 fader