Before ARP, Ken Freeman had invented the concept at the beginning of the 1970's with one of the evolutions of his former Freeman string symphonizer designed at the end of the 60's. But it hadn't any success at this moment (it gains a humble success later and now it costs a fortune). He talks about it in this great article on SoundOnSound.
Now, I'm going to copy/paste a short extract of the excellent book (available also in ePub and Kindle formats) "Creating Sounds from Scratch: A Practical Guide to Music Synthesis for Producers and Composers", by Andrea Pejrolo & Scott B. Metcalfe.
All the string-synths were paraphonic. This paraphony made the success of many brands, as I wrote above. And it keeps on having a great success. Today there are again numerous synths which provide the real paraphony in addition to the polyphony, and even today in 2018 among the Moog, Dave Smith, Waldorf, Yamaha, Roland, etc. instruments. And in all the brands which produce the most awesome "organ-synths" as I showed in previous posts. Because it is impossible to do with the common polyphony several things which are produced only by paraphony for incredibly beautiful results.The mid-1970s saw another solution called “paraphonic.” A paraphonic synthesizer allowed several notes (four or eight was common) to sound simultaneously, but all would share the same filter and/or envelope generator—meaning that as soon as the first note began, the envelope shape would begin as well; any subsequent notes would join the envelope shape in progress rather than starting from the beginning with its own envelope shape (see Figure 1.17). This is a little confusing, but consider the example of a real piano: As each note is struck, it follows an envelope of fast attack and long decay, regardless of whether the notes are hit concurrently or in sequence. With a paraphonic synth, several notes can sound concurrently but the envelope and filter shape are all tied to the first and last notes that were played. The paraphonic design was useful for pad sounds.
Figure 1.17
Graphical illustration of monophonic, paraphonic, and polyphonic envelope shapes.
In paraphony the common architecture of the synth is a divide-down architecture. There is not an oscillator for each key of the keyboard, but a very short number of oscillators (between 4 and 12 regard the design of the model to cover... simply an octave). Then it is by divisions of the frequency that the other octaves are produced. So all the keys have the same phase. The resulting sound of all these "phase-locked" oscillators is of course very different of the resulting sound of free phased oscillators. And no need to tell that it is also impossible of course with samples.
So you have a short number of oscillators to cover all the range of the keyboard, whatever the number of octaves. It is a concept named "Divide-down" architecture. And the paraphony means that in addition to this divide-down architecture, all the oscillators share... a same unique VCF and a same unique VCA.
If you press a new key before releasing the current active keys, the envelope of the VCF continues its curse with the new key in addition to the already pressed keys, without any new trigger for this new note. The same for the VCA. It means that there is no new trigger of the envelope of the (unique) VCF neither of the envelope of the (unique) VCA. These envelopes are retriggered only if there is no currently pressed key. That's why string-synths are so good for evolving pads, drones, symphonic ensembles, etc. All the best cosmic rock, krautrock, and prog-rock pads have always been made by paraphony.
And now, some videos again, showing the paraphony in action :
Marc Doty introduces the Strings part of the ARP Omni:
Marc Doty now introduces the paraphonic envelopes (named "Single Trigger" in this synth) of the ARP Omni:
And in this third part where both sections of the ARP Omni are used together, he explains a bit better what is a divide-down architecture and the paraphony:
Etc.
