A digital sequencer is a sequencer that uses a microprocessor and RAM to remember and play back sequences of notes. Although it's digitally controlled, the output usually consists of analogue CV and gate signals.
With the exception of coarser, looping digital step sequencers, digital sequencers tend to conceptualise music as a handful of monophonic parts, each playing a single long list of notes which can start and end on arbitrary points on a fine (usually 24 PPQN) grid.
A digital sequencer works by turning each note into at least three numbers, representing its start time, length, and pitch. Some can store additional values, useful for details such as velocity. It can store these numbers in a handy list, and then read them back out again to play them.
All these numbers are simplified, quantising the pitches to twelve-tone equal temperament, and the timing to a simple grid. This is still a far more versatile system than its analogue predecessor, which has a far shorter list and far coarser grid. The notes can be different lengths. So can the gaps between them. Nothing has to repeat, with a song consisting of thousands of completely independent notes. You can likely even save the list of notes to a cassette tape as raw data.
In effect, the step sequencer's short, looped phrases of eight or sixteen equidistant notes have been replaced by a whole song's worth of thousands of notes.
This was the approached pioneered by Ralph Dyck's Digital Sequencer, which impressed Roland so much they hired him to help evolve it into the MC-8 and its successor, the MC-4. Once MIDI came along, this framework was adopted by almost all MIDI sequencers.
Vince Clarke suspected that the MC-4's tight timing gave Chorus its distinctive sound, but I think it's more likely the result of having exclusively monophonic parts, each played on a custom patch on an analogue subtractive synthesiser.
The revolution in electronic music didn't happen when they invented the DX7 or the Prophet-5. It happened when they invented the sequencer. It enabled me to program something I could only dream of, which is what I do. I imagine it, and then I make it happen.
— Vince Clarke, 2022
- "Vince Clarke" Paul Ireson, Sound On Sound, Dec 1991
- "Vince Clarke: The Idea and the Song" Bren Davies, Tape Op, Jul 2022