Purdue students' device creates guitar "wah" effect without physical pedal

Electric guitar players soon may be free to walk anywhere on stage during a performance or rehearsal and still activate "wah" pedal-type distortion effects by using technology created by eight Purdue University students. For their senior project, students from Purdue's School of Mechanical Engineering developed the Ghost Pedal, a wireless device that uses sensors attached to the guitar player's foot to create the distortion effect. The conventional wah pedal alters the tone of an electric guitar to create a distinctive effect that mimics the human voice. The Ghost Pedal team includes Garrett Baker, Will Black, Matthew Boyle, Brett Hartnagel, Christine Labelle, Adam Pflugshaupt, Nick Sannella and Robbie Hoye. The students graduated from Purdue in 2011 with Bachelor's degrees.

Hoye says traditional wah pedals limit where guitarists can perform during a concert due to demands of the music. "During a performance, the guitarist uses and changes audio distortions by stepping on pedals. While vocalists and other band members can move around the stage to interact with the audience and each other, the guitarist is often restricted to the space around the pedals," he says. "Because Ghost Pedal is wireless and does not have a physical pedal, guitar players can activate and use their wah distortion effect anywhere on stage at any time. They also have the ability to deactivate the effect whenever they choose."

Hoye says Ghost Pedal is made of two sensors attached to the guitarist's ankle. "The variable resistor sensor records what the user is doing with their ankle, and a sustain sensor either accepts the transmission feed or ignores/sustains it. These signals are conveyed to a microcontroller that uses them to control resistors within the wah circuit, which affects the wah effect. Ghost Pedal uses a digital potentiometer to bridge the gap from a digital circuit to an analog circuit, so audio signals from the guitar always stay in their original analog format. This allows the guitarist to maintain the clearest sound possible." Once Ghost Pedal is turned on, the user enters a 10-second mode during which the variable resistor calibrates the ability to flex the foot from the floor in a normal pedal motion. After calibration mode, the guitarist enters freeplay mode. "During freeplay, the user actively manipulates the wah level by changing their foot's angle from the floor."

While in freeplay mode, the guitarist can hold the resistance level at a constant by tapping the sustain sensor with the other foot. This allows the guitarist to move on stage - jumping, running, spinning - without changing the wah effect. Tapping the sustain sensor a second time puts the guitarist back in freeplay mode, which allows the wah level to be manipulated again.

Hoye says using Ghost Pedal is intuitive. "The calibration mode adapts itself to modify the resistance sensor to each user and their foot flexibility at the touch of a button. Ghost Pedal and traditional wah pedals use the same motion to activate the wah effect; the guitarist doesn't have to learn a new motion. Activating and deactivating the effect by tapping the sustain sensor can be mastered after a few practice attempts."

Although Ghost Pedal was designed with wah capabilities only, Hoye says the device's functionality may be developed further. "Companies that sell distortion effect devices will have the ability to modify Ghost Pedal to play off of any effects unique to their business from stomp box effect pedals to volume control pedals."

The patent-pending Ghost Pedal is available for licensing through Eric Lynch, project manager in the Purdue Office of Technology Commercialization, at 765-588-3477, eslynch@prf.org

A video about Ghost Pedal - including Will Black, a member of the Ghost Pedal team, performing with the device - can be viewed at http://www.youtube.com/watch?v=R_GzNPT_8vk