In the mid-70s synthesizer designers started looking into a new market - guitar synthesis. The idea was that a guitar could be used to control a synthesizer via circuits that converted pitches to control voltages. As there were many more guitarists than there were keyboard players and synthesizers offered so many new sounds, the motivation was that this could be a lucrative market to move into.
The first guitar synthesizer I can find was the "Polyphonic Guitar Synthesizer" created by Bob Easton of 360 Systems and he followed up with the Slavedriver and Spectre. A few years later in 1977, Roland released their GR-500 / GS-500 combination and Korg followed with their X-911 Guitar Synthesizer in 1979.
ARP also ventured into this market and their story is particularly interesting because it was brave and innovative, but ultimately attempted before the technology available was able to handle their ambitions and it sadly came at a price for the legendary company.
The project started with a huge six-voice polysynth that would have both a guitar version and a keyboard version. The guitar version was dubbed the "Centaur VI".
Thanks to the help of the Alan R Pearlman Foundation I had the pleasure of interviewing David Friend and Bill Singer of ARP who worked on the Avatar project for my documentary "Electromotive - The Story of ARP Instruments". Found at 1:17:19 in the embedded link below is the specific section of the film where we cover this bit of musical history.
Please take a moment to check out the Foundation here:
One of the engineers who worked on the Centaur VI passed on what he could recall about its features.
Two oscillators per voice with each oscillator generating four footages (like an organ) that could be combined to create square waves or sawtooth waves.
ARP's 4-pole filters.
Two ADSR envelopes and an envelope follower.
The far left panel could be interchanged for the guitar or keyboard interface for the planned polysynth.
Above: David Friend working on the Centaur VI and Bill Singer ready to play it from his guitar. These photos were taken by ARP's then VP of Marketing Worldwide, Bob Hoffman, at Pete Townshend's studio during a demonstration of the Centaur and Avatar. They are reproduced here with permission.
As discussed in "Electromotive...", the Centaur VI just wasn't viable as a product due to the sheer amount of components required to build it and their associated cost. The estimates were that it would have had to have been sold for around $15,000 per unit and that's around $64,000 when adjusted for inflation, so it's not difficult to understand why ARP abandoned the project having made only one prototype.
ARP had also been working on a more affordable monophonic guitar synthesizer, the Avatar, and that did see the light of day at a more reasonable (but still pricey) $3,000 which is around $12,700 when adjusted for inflation.
Here's some photos of Bill and David demonstrating the Avatar with some famous faces from the same session as the Centaur.
The pitch to CV solution for the Avatar was a bespoke hexaphonic pickup designed by Ron Hogue that was essentially six pickups in one. This then gives you six signals that run through some very unusual connectors with coax so that they remain isolated.
As the synthesizer section is monophonic, only the strongest signal is sent through the synth and there are in fact individual switches to allow the player to define exactly which strings the synth should read from and which to ignore.
Here's a description of how the Avatar converts pitch to CV that Nathan @ Synthchaser kindly helped me with.
In a nutshell, we count the number of cycles of a very fast clock during each cycle of an incoming note, which measures the period of the note. The number of clock cycles counted is transferred into a digital memory location or "register".
The value in the register is used to divide down a second clock and this creates a square wave that can be converted from a frequency to a control voltage which in turn, is directed to the synths oscillators to sound a note that matches the one you played on your guitar.
The wave shape created by a guitar is too complex to be used directly, which is why the conversion to a square wave is necessary.
The main synth section of the Avatar is essentially a mark III ARP Odyssey and if that's all it was, it would seem pointless given that an Odyssey already existed and worked perfectly well from its keyboard.
But that isn't all the Avatar is, far from it in fact, as the audio from the hexaphonic pickup also runs into the synth. As this isn't controlling any oscillators it remains polyphonic and is a very unusual sound because there is no cross-talk between any of the strings. As well as the clean hexaphonic sound, there is a switch labelled "hex fuzz" which runs each string through its own isolated fuzz circuit to create an effect that was nicknamed "clean fuzz". The guitar signal (clean or fuzz) comes out in stereo with strings EAD on one mono output and strings GBE on another. The monophonic synth sounds come out of yet another output.
You can also run external audio into the Avatar and as you're not using the normal output from your guitar, you can run that through some pedals and then into the synth for yet another sound source. Or you could run that into an amplifier as you would normally and have a huge wall of sound coming from a single guitar.
The Avatar is also designed to properly integrate with the guitar so there is an envelope follower, string trigger control and string CV control.
There were also three foot switches and a foot pedal for the Avatar to control:
Switch 1: System on / off
Switch 2: Portamento on / off
Switch 3: Infinite sustain on / off
Pedal: Oscillator 2 frequency and/or filter cutoff
When I'm able to record some demonstrations with my Avatar I will upload them, but in the meantime check out this recording from 1978 featuring the Avatar by David Torn and Drew Schlesinger.