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Hot Hand puts effects at guitarists' fingertips

Posted: 01 Jun 2006     Print Version  Bookmark and Share

Keywords:R. Colin Johnson  automotive  accelerometer  audio processor  Hot Hand 

It's the stuff of rock 'n' roll fantasy: a ring that gives its wearer the power to morph the sound of an electric guitar at will. Thanks to the pairing of an automotive airbag accelerometer with a customized version of a popular audio processor, a technology called Hot Hand claims to make that scenario possible.

Devised by Analog Devices Inc. spin-off Source Audio LLC, Hot Hand puts an ADI accelerometer chip in a ring that guitarists place on a finger of their picking hand. The movements of the ring are tracked by feeding the wired control signals into a box that houses an ADI-customized SigmaDSP—a 56bit audio processor with 24bit ADCs and DACs, and a 100dB dynamic range. Two foot pedals control on/off and cycling through user-defined presets.

"Hot Hand is one of the most innovative new sonic tools for guitarists, especially in home studios, where players have the time to experiment," said Michael Molenda, editor-in-chief of Guitar Player magazine. "Hot Hand will likely be popular among adventurous players looking for unique ways to manipulate the sound of their guitar. It may not appeal as much to live performers, especially guitarists who don't move around much on stage," since hand movements achieve the effects.

But "I tried it out at a gig," Molenda said, "and for me, it was very cool being able to use physical gestures to control my guitar effects."

"We have been making MEMS devices now for almost 20 years, and we continue to be amazed by the novel applications that engineers can come up with for our sensors," said Christophe Lemaire, business development engineer at ADI.

Source Audio was founded by two former ADI employees: Roger Smith, the spin-off's president, who at ADI had been director of audio products, and Jesse Remignanti, VP of engineering at Source Audio and a former audio systems and software engineer at ADI. The pair convinced their former employer to create a customized version of its SigmaDSP for an SoC called the Sound Audio 601 (SA601), to complement the low-power version of an ADI accelerometer chip (the iMEMS ADXL320). The co-founders then recruited former Kurzweil Music Systems Inc. chief scientist Bob Chidlaw to craft the effects.

Source Audio's first Hot Hand version applies the SigmaDSP-iMEMS combo to achieve wah-wah and volume effects. Other guitar effects are slated to follow soon.

"While working on SigmaDSP chips at ADI, we got the idea to combine SigmaDSP with an accelerometer chip, and that insight gave birth to Source Audio," said Remignanti. "Then we brought in Bob Chidlaw to make it sound great. He's the sound designer of Kurzweil's famous sampled piano sounds, which virtually redefined synthesizers."

Among the volume effects possible with Hot Hand is the use of a slow attack envelope to simulate the sound of a bowed instrument such as a violin. Other volume control effects include tremolo, or amplitude modulation. Ordinarily, tremolo is controlled by a low-frequency oscillator, but in Hot Hand it is controlled by waving the fingers, hand, wrist or forearm.

"With volume you can do swells by hitting a chord and then raising your hand to come on stronger, and you can get tremolo effects whose speed is controlled by your hand position," said Remignanti. "We don't use just standard wah-wah effects, although we do have one that is an accurate model of the original Cry Baby [pedal effect popularized by Jimi Hendrix], which Bob Chidlaw did with a methodically crafted mathematical model.

"Our new wah-wah effects combine both low-pass and bandpass filters, plus what we call multipeak filters, which are like two or more wah-wahs moving in sequence against each other and are unique to Source Audio."

Source Audio's next effects implementation has already been prototyped. It will use the same hardware setup, but will offer flanger (signal delay) and phaser (signal filtering and remixing) effects. These are achieved via comb filters with moving bandpass peaks that typically are controlled by a low-frequency oscillator but, in Hot Hand's case, are controlled by gestures.

"We expect to have our first Hot Hand wah-wah off the assembly line within three weeks, but Hot Hand is not just for wah-wah effects. It's a whole new way of controlling any effect," said Remignanti.

He said the company hopes to demonstrate the prototype flanger and phaser capabilities at the National Association of Music Merchants show on July 14-16 in Austin, Texas.

- R. Colin Johnson
EE Times

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