New Type of Acoustic Guitar Processing

Paladin

This is a snippet from EETimes.com about a new type of DSP for acoustic guitar.
Basically you plug your guitar through this effect (pedal? POD?) so that the output sounds more like a studio guitar sound for your live playing.
I dont know anything else about it. Anyone heard about this?

Fishman's digital acoustic imaging algorithm works by comparing the sound of a guitar under perfect conditions—in an ultraquiet studio with a variety of expensive condenser microphones placed at various distances in front of it—with the signal you get from a piezoelectric transducer or pickup, which Fishman places under the bridge saddle. The transducer senses the originating excitation of the strings, but is not sensitive to the sound hole resonances. And it doesn't hear the mix of phases in front of the instrument as various frequencies radiate differently off the top, sides and head of the guitar.

Fishman says it can capture and re-create all these subtle frequency and phase differences by running its algorithm on a Blackfin DSP from Analog Devices (Norwood, Mass.), contouring the audio from the raw transducer so that it sounds as if were in the studio.

"First, we take a guitar into the studio and do a two-channel recording—one channel records from what the transducer hears and the other channel records what the microphone hears," said Fishman. "Then we run the algorithm we developed to make a very close comparison of the two signals in the frequency domain, subtract one from the other to get their difference, then convolve the two to get what we call a sound image."

From the sound image, Fishman Transducers creates a custom filter with more than 2,000 frequency taps for the Blackfin DSP. "We not only adjust the amplitude of each frequency, but also make critical-phase adjustments, which is where the magic comes in," Fishman said. "Without that phase information, we would just have a 2,000-band graphic equalizer. But by adjusting the phase information too, we get three-dimensionality in the sound."

Eoin Madsen

That was the concept behind the Fishman Aura, which has been around for a few years now. It's already in its second incarnation.

I tried the original (and did recorded comparisons) - it totally failed to deliver. As far as I could tell, it was basically just convolution. Nice variety of sounds, but not at all achieving what it set out to achieve. Perhaps the technology has moved on a bit since then. I'm sure it will become the norm for live acoustic processing sooner or later. Though the potential of DSPs in live engineering is surprisingly unrealised so far.

Paladin

This is sort of interesting for me as my company is building the microprocessor for this, but to be honest I am still skeptical. Generally DSP is a lot of fun and great for some things, but I think the subtleties of acoustic live are still a little boyond current DSP.

I do think it will become the norm eventually though.