Machine Design

Accelerometer gives guitarists a hot hand

Until now, musicians playing electric guitar relied on foot-operated pedals to control filters and other special audio effects.

But pedals are limited in speed and range, and they restrict how much a musician can move on stage. Engineers at Source Audio LLC, Woburn, Mass. (, have come up with an alternative, Hot Hand, that uses a dual-axis accelerometer from Analog Devices ( The device frees guitar players and gives them more flexibility in shaping the sounds coming out of their guitars. It also lets them add some showmanship to their performances.

The micromachined 5-g accelerometer is small enough to be worn as a ring, usually on the guitar player's strumming hand. It detects accelerations in two planes, sensing motion and tilt of the guitar player's hand. Signals from the ring are converted from analog to digital and fed into a 56-bit audio processor with a 100-dB dynamic range.

They are sent through a low-pass filter to eliminate unwanted frequencies due to jitter in the guitarist's hand and other sources. The guitarist can also adjust the filter's cutoff frequency to match a playing style or to get a particular sound. The motion knob on the Hot Hand control unit changes the filter's cutoff from 2 to 20 Hz. In the first-generation Hot Hand, the signals control various resonant filters and let the musician dynamically sweep these filters, creating what is known as wahwah effects. The device can be easily calibrated and runs for up to 20 hr on four AA batteries.

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