In the previous articles introducing the synthesizer, we looked at the basic building blocks of a basic front panel – if you haven't read them yet, here's your chance to get caught up:
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In this third part, we'll be looking at how many notes you can play at once on your synthesizer – as well as why, and how it works.
The question of polyphony
The word note usually means a musical note. We talk about notes in a scale, quarter notes vs. half notes, or a particular sequencer that can record up to 256 notes.
A voice usually means the “machinery” that’s needed in order for an instrument to play one note. The number of simultaneous voices an instrument has — the number of notes it can play all at once — is its polyphony.
Unlike acoustic instruments, a synthesizer’s polyphony can’t be guessed at by looking at it. A grand piano has 88 keys, and if you fall on it and hit them all, you’ll hear them all: that’s 88-voice polyphony.
Monophonic
If a synthesizer only has enough modules to create one voice, it doesn’t matter how big its keyboard is. It can only play one note at a time: it’s monophonic.
Now, there are a lot of monophonic acoustic instruments — the flute, for example. But in all the history of keyboard instruments, from the organ to the harpsichord to the piano, none were monophonic. When synthesizers became a thing, however, monophonic voicing also became a thing – mainly because it was expensive, and complicated to deal with the circuitry of more than one voice. One voice could also bring a lot to the sonic table, in terms of timbre and note shaping, using the synthesizer's filter and envelope.
In Synth Gems 1, you’ll see a historical trend from early monophonic synthesizers (mono synths) to now-common polyphonic synthesizers (poly synths), with some interesting side trips along the way. Let’s continue with a few words about polyphony and technology.
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Polyphonic
By definition, any synth that can play more than one note is polyphonic. However, based on the technology limitations of a given time period and the design choices they require, there are various types of polyphony.
It’s now common to define a polyphonic synthesizer as one that has a complete signal path for each voice — at least one VCO to make a sound, a VCF to shape its tone using an envelope, and a VCA to start it and stop it using another envelope. This is often called “true polyphony,” but there’s nothing particularly “false” about poly synths that don’t have it.
As you can see from the diagrams, the more polyphony you want, the more modules you need. It took years to go from poly synths that were astronomically expensive and delicate to ones that were reliable and affordable. In the meantime, some designers came up with a practical way to give players the polyphony they wanted... sort of.
Electronic instruments like organs can play as many notes as there are keys — but they have none of the articulation (note shaping) you’d get from VCF and VCA envelopes on each note (which polyphonic synthesizers have). However, it turns out there’s a trick to simulate that articulation without a lot of extra electronics – see below.
Paraphonic
In a paraphonic synthesizer, there are oscillators for every key — but they’re all sent at once through a single VCF-VCA chain with one pair of envelopes. Clever keyboard control over which notes trigger the envelopes can add a sense of articulation.
Paraphonic synths can play more than one note at a time, but at some point in the signal path, all notes are combined and processed as if they are one sound.
On some synthesizers, that might mean multiple oscillators (like a divide-down network) going through a single filter and amplifier with single envelopes; this creates what can sound like a single articulated note whose pitch changes as it evolves.
On others, individual oscillators might have their own amplifiers to articulate their notes separately, but then go to a global filter – leave the filter open and you have polyphony, but open and close the filter, and some of the individual note articulation can be obscured.
In 1981, KORG released the Mono/Poly. Interestingly, how the keyboard plays the VCOs, called the Key Assign mode, can create a variety of different behaviors.
In Unison mode, the Mono/Poly operates like any other analog monophonic synth, albeit with the massive sound of four VCOs.
In Poly mode, up to four notes can be played at once, with one VCO per voice – but instead of every voice sounding exactly alike as you’d get with a divide-down synth, the four notes could be set up with drastically different timbres.
In Chord Memory mode, monophonic playing follows a chord voicing set by the player, with each VCO playing a different voice.
Finally, in Unison/Share mode, oscillators are distributed between voices playing at that moment – play one note, hear all four VCOs; play two notes, hear two VCOs per note; play four notes, hear one VCO per note.
The Moog Matriarch, featured in-depth in Patch & Tweak with Moog, has different voice modes, not much different from the unison and poly modes of the KORG Mono/Poly.
While it’s true that paraphonic synths don’t have the nuance of later poly synths, they can still be fun to play while sounding beautiful. Below, you can see and hear the paraphonic Moog Matriarch along with other monophonic synths.
Check out this amazing performance by Lisa Bella Donna where she uses a paraphonic Moog Matriarch, the monophonic Grandmother and these mono synth modules: Eight Mother-32s, two DFAMs, and two Subharmonicons. All these synths also have sequencing functionality built-in.
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