Home -> Magazines -> Issues -> Articles in this issue -> View
The Musical Micro | |
Article from International Musician & Recording World, January 1985 |
The next in Liz Coley's sequence of computer features
We're all aware of sequencers. I don't know about you but I cringe every time I hear one of those short, flat, endlessly repeating patterns that some technofreaks seem to love. Even less inspiring are the two-note bass lines that many a stark synth outfit have a fetish for. Still, it's hard to be imaginative in the use of standard sequencers, bearing in mind their severe limitations. But, before we look at these limitations it's as well to understand how the things work.
The earliest sequencers were analogue. I'm not going to go into how these worked 'cause it's pretty irrelevant now, but they were difficult to use, unreliable and dealt in tens of notes as opposed to hundreds or thousands — you had to select a pitch for each note by twiddling a potentiometer knob to set the required control voltage! Anyway, you've probably heard them in action on many a 70's Pink Floyd album — little more than arpeggiators really. At this point I should explain that nowadays synths assign notes to keys in a more-or-less standard manner ('scuse me if you know all this). Each synth key generates a different control voltage (CV) when pressed. Very early in this decade the first agreement amongst major synth manufacturers set a standard for CVs at one volt per octave. Now, these CVs set the pitch of notes but in order to define the way a note is shaped, the associated envelope generators (EGs — usually just attack, decay, sustain and release) must be 'gated' on as well.
So, normally when you press a key an EG gate signal is generated in addition to the appropriate CV and continues as long as the key is held down. If the EGs aren't gated when you press a new note, you get a 'legato' effect — a slide between notes under the control of the last envelope gated... like picking a note on a guitar and sliding from fret to fret without re-picking. Now, if that's all clear to you you'll see that to 'sequence' — play a preset pattern of notes and rests — all you have to do is throw the appropriate CV and gate signals at the synth with the required time intervals between them, remembering that each synth voice requires a separate, independent CV & gate input. Most sequencers for general use work in this manner, hence the CV and Gate sockets fitted to all synths BM (before MIDI), though some now have both. That understood, we can take a brief look at the workings of a monophonic digital sequencer.
Inside each digital sequencer is a very simple computer that takes 'step time' or 'real time' instructions (or both) as to the assignment of note values/rests to a fixed number of pattern 'steps'. These can be replayed at a variable tempo by generating the required CV and gate signals with the appropriate timing between steps. The number of steps available is limited by the amount of memory built-in. Here I must pause and make clear what I'm going on about:
Step time means pre-programmed — workout the required timing relationships between notes plus note values, then enter the info one piece at a time.
Real time means play the pattern required on the keyboard and the sequencer records it, or the closest it can get to the pattern according to the step resolution set.
Steps form the sequencer pattern: suppose you have a 100 step sequencer: the 100 steps could be ranged over, say, two bars of a song structure giving you 50 steps per bar — a high resolution that allows a bit of rhythmic expression or complicated riffs... but the sequencer is limited to those two bars and repeats only. If you range the same 100 steps over a more luxurious 10 bars at the same tempo, you only get 10 steps per bar so the resolution is low.
So, here we have the first limitation — a maximum (and usually low) number of pattern steps allowing you only short complicated patterns or long simple ones.
Polyphonic sequencers are merely monophonic sequencers in boxes, all with the same number of steps, all under the control of a master timing clock (this is really just synchronisation). This gives you separate voice channels where chords are sequenced by assigning each note of the chord to a different channel with the same step number, so the notes are played together.
That's just about all there is to it. Manufacturers offer different numbers of maximum steps and various sequence editing features, but basically... that's it. Any further features go beyond CV and gate inputs (pitch selection and EG gate only, remember) and force the sequencer to at least be special to one particular synth and probably built into it... until MIDI.
MIDI is a great idea. The above problems forced manufacturers to agree on a standard system for controlling all the functions of a synthesizer — pitch, voice, note on/off, volume, touch sensitivity, patch changes, patch programming, etc, etc. The upshot is that with a MIDI equipped synth (or 12), plus a home computer, you have the basis of an immensely powerful and versatile composing, sequencing and performance system with only a couple of minor drawbacks. Next month reveals all.
Digital Signal Processing - An introduction (Part 1) |
Music On The PC |
Software Support - Hints, Tips & News From The World Of Music Software |
On the net |
Software Support - Hints, Tips & News From The World Of Music Software |
![]() Software Support - Hints, Tips & News From The World Of Music Software |
A Time Trip - Ready:_ |
![]() Basically BASIC (Part 1) |
CAMI - Pitch Training On The BBC Micro (Part 1) |
Lab Notes - Computer Drums |
Synth Sense |
Step-time Composition on the Model 64 |
Browse by Topic:
Feature by Liz Coley
mu:zines is the result of thousands of hours of effort, and will require many thousands more going forward to reach our goals of getting all this content online.
If you value this resource, you can support this project - it really helps!
New issues that have been donated or scanned for us this month.
All donations and support are gratefully appreciated - thank you.
Do you have any of these magazine issues?
If so, and you can donate, lend or scan them to help complete our archive, please get in touch via the Contribute page - thanks!