Here are some photos of my EML Poly-box. Polyphony (or the number of sounds/voices that an instrument can make at once) has always been a challenge to manufacturers of electronic instruments. In analog synthesizers, the number of circuits multiply with every added voice, so if you want to play a 4-note chord, then you need four times the amount of circuitry required to make a single voice.
Even in the digital realm, most synthesizers have a maximum number of voices that they can simultaneously produce because of the number of calculations required for modeling the sounds.
In the 1977, EML (or Electronic Music Laboratories) had a solution to the problem of polyphony. They developed this tool, which essentially takes an external audio signal, tracks the frequency, then outputs a chromatic scale of pulse waves based on that frequency. The idea was that you can use modular synthesizers to patch in chords of notes, rather than single oscillators. This was not a very popular product at the time because a lot of other solutions to polyphony, like polyphonic synthesizers, started hitting the market. This box came in black and orange (like the one that I have). Only 130 were reportedly manufactured. I am not sure if this is the total number of both colors combined, or of the orange.
So how does this sound? On its own - if you switch to its internal pitch reference, it is very bland. The tone of the output sounds like the blandest organ imaginable. There is no envelope, so an organ (note on off) of square waves is a fairly accurate description of its sound. The one positive addition to the organ scenario is that it does have a second squarewave that can be detuned (phasing control)or shifted 1 or 2 octaves(octave couple switch) away from the reference pitch. In addition to this, the combination of the 2 squarewaves can be transposed by 1 or 2 octaves down. This makes the tone a little more interesting. It also has a brilliance control that is much more like a treble tone control on a stereo than a filter of any significance.
The magic happens when you process other synthesizer sounds through this box. Now granted, this box does not track the timbre of the incoming signal, nor is there any kind of envelope or volume contour tracking. But it does track the frequency with great precision. Even better than most guitar octave pedals, this box is very accurate to the point that not only will it track vibrato and sudden changes in the pitch of the input, but it will track simple FM modulations to some degree: If I put an audio oscillator from a modular synthesizer into this, then use a second audio oscillator to modulate the first, the poly-box responds and tracks the cross-modulation of these two oscillators!
Another interesting thing about this box is the way it sounds when you try to confuse it. There are 2 ways to confuse it: first, by trying to input multiple frequencies, as in a chord or a mix of 2 oscillators sounding simultaneously; or second, by sending an oscillator through a highly resonant filter before processing it with the poly-box. Both of these result in entertaining sounds that can't easily be produced any other way.
One of my favorite things to do with the Poly-box is to make tone clusters for adding some noise or chaos to a sound - especially for percussive sounds. One can track the pitch of another oscillator, then hit several notes in the same area to make a more chaotic cluster of tones, then mix it slightly in with the tracked oscillator.