Making Music with Machines, A-Term 2025

Collin Keegan, Marzuq Mir, Sean Smith

Overview

The Digital Reed Aerophone (DRA) is a digital woodwind instrument that utilizes a valve as a reed to excite the air column. Air is supplied by a seperate pump through the valve which oscillates at the fundemental frequency of the note that is being played. Six tone holes are used to vary the length of the air column providing an additional avenue of pitch adjustment, and are controlled by individual servo motors.
The goal of the project was to exeperiment with the idea of using a valve in place of a reed in a woodwind instrument, and to explore what sonic benefits could come from decoupling the reed frequency from other factors. The instrument is capable of varying pitch in 3 ways: opening and closing tone holes, adjusting ‘reed’ frequency, or a combination of the two.

Construction

Resonator:
The resonator for this instrument was constructed from 1-1/4 in. PVC pipe. The length of the tube as well as the location and size of each tone hole was determined using an online flute hole calculator (shown below). We opted to not drill the thumb hole (LTh) due to its proximity to L2. The length added by the corners was approximated and taken into account into the length to cut the PVC at. Only 48″ of pipe is required, as the corners add enough length to make up a bit more than the distance required.

Tone Holes:
The tone holes are covered by a lever with 3/16 in. thick foam tape applied to them and are actuated by servos, held to the tube using a 3d printed c-clamp style mount. Each hole is 1/2 in. in diameter, and the key chosen for the range of the instrument were based on the expected capabilty of our valve to reach the required frequencies. We did not tune the frequencies of the valve to necessarily match the intended frequency of each hole described by the calculator, but rather just tuned them based on the point where it resonated with the most volume.

Electronics and Software

Controls and Power:
All of the electronics for the instrument with the exception of the pump are controlled by a Raspberry Pi Pico and programmed in C. Each of the six MG996R servos are controlled by PWM pins on the Pi, and the valve is driven by an H-Bridge motor driver.
Power for the system comes from three external benchtop power supplies- One for the valve, another for the solenoids, and the third for the pump. This was less of a design choice and more of a decision dictated by our unique access to numerous benchtop supplies.

Valve:
The valve we used is an Adafruit 4663. The valve frequency is controlled through multiple factors- PWM period, duty cycle, and a second layer of PWM within the “on” portion of the first, to step down the “on” voltage closer to the intended voltage of the valve, as the power supply we used was supplying 12V rather than 6V. By driving the valve with a motor driver rather than an NMOS, we were able to actively push and pull the valve open and closed rather than relying upon a slow spring return. Because of this, at higher frequencies the valve was not opening or closing fully, but rather oscillating in between while never fully reaching either state. This had the benefit of reducing the volume produced by the valve, as when playing slower frequencies that allowed enough time for the valve to cover its full stroke, an audible ‘click’ sound was made upon each impact.

Pump:
The pump we used was made up of a 3d printed impeller and housing coupled with an RS550 Motor, which we found preassembled for free. We chose to use an impeller style pump due to its continuous and consistent airflow. We powered the pump directly from an external 12V power supply. Due to its volume, we placed the pump inside of an insulated box during operation to isolate noise.

Servos:
We opted to use MG996R servos to actuate the tone hole levers, with control coming from PWM pins on the microcontroller and power coming from an external 5V power supply.

Interaction and Composition:
The DRA is setup to be controlled via Ableton Live via a serial communication MAX patch created by Scott Barton. Each pitch is stored in an array and mapped to a MIDI note value. At the time of writing, 13 distinct pitches or methods of pitch production are programmed, which can composed for in MIDI or played in real time through a MIDI keyboard or other MIDI controller.

Documentation

Video:

Audio After Filtering:

Part Name	MPN	Link	Quantity	Total Cost
Resonant Cavity	2ft 1.25in PVC Pipe	PVC Pipe	2	$13.62
PVC Elbows	1-1/4 in. x 1-1/4 in. 90 Degree PVC Socket x Socket Elbow Fitting	PVC Elbows	2	$5.18
PVC Coupling	1-1/4 in. PVC Schedule 40 S x S Coupling	PVC Coupling	1	$1.24
PVC End Cap	1-1/4 in. PVC Schedule 40 Socket Cap	PVC End Cap	1	$1.59
Microcontroller†	Pimeroni Pico LiPo	Pico	1	$18.00†
Valve	Adafruit 4663	Valve	1	$2.95
High Torque Servos◊	MG996R	Servos	8◊	$32.00
Breadboard	Busboard BB830	Breadboard	1	$8.75
Pump Motor†	RS-550VC-7527F	Pump Motor	1	$21.00†
Air Reservoirs† **	Clippard AVT-32-16	Reservoirs	2	$142.96† **
Air Hose	5/16 in. O.D. x 3/16 in. I.D. x 20 ft. Clear PVC Vinyl Tube	Air Hose	1	$6.56
Barbed Fittings	3/16 in. Barb x 1/4 in. MIP Brass Adapter Fitting	Barbed Fittings	2	$12.94
Pipe Nipple	1/4 in. x 1-1/2 in. MIP Brass Nipple Fitting	Pipe Nipple	1	$5.75

† This item was free or already owned and did not contribute to our overall cost.
◊ Only six were used, but came in packs of 4.
** The Reservoirs used were chosen because we already owned them and therefore added no cost. Any attempt to reproduce this instrument should not use these reservoirs if purchase is necessary, as they are extremely overkill for this application.