In my spare time (??) I’ve been de-constructing and re-constructing some iMS-20 patches to show some of the fundamentals of analog synthesis. The patches here are based on patches from the built-in templates. I will add more of these sporadically unless I am blessed with a big stretch of free-time to play. These patches will also work on the MS-20 and MS-20 Mini though the effects will need to be added externally.
iMS-20 Block Diagram
The iMS-20 is a seriously fun App with a fairly deep semi-modular architecture. In the patch bay, some of the patch points will break the connection while others will mix the signal (audio or control) into the path. The points that break the connection are shown in red here. Click to enlarge!
Differences in the Hardware MS-20 and iMS-20
- Basically identical except for some markings on the patch bay
- can not actually plug an external instrument like guitar into EXT on iMS-20
- MS-20 is a monophonic synth, iMS-20 is actually seven (7) MS-20’s in one unit
- the restrictions are:only one of the 7 can be used with the Synth Sequencer (aka Synth); the other 6 must be used with the Drum sequencer
- When using the synth to create drum patches, these patches do not include: Portamento, EG1 Release, EG2 Hold, EG2 Release, MG does not have Key On/Off switches
- However, the “drum” parts can actually be synth parts as well, but they must be controlled with the more restrictive Drum Sequencer
- Many of the sounds actually consist of 2 parts: a synth part and a sequencer part that uses gating to chop part of the sound up (eg Kick sound in the SyNC template)
- VCO1 and VCO2 have different ranges. VCO1 can be set to a lower range (32’ vs VCO2’s 16’) but VCO2 can be detuned a full octave down (-12) to match VCO1 if needed.
- Placing the EG2 Sustain Level at 0.0 will produce the drum transient sound.
- Resonant Filters will self-oscillate even when the VCOs are turned all the way off! When the Q goes above about 7.50. This is used in Drum patches. The Filter Cutoff determines the resonant oscillation frequency. Can be used to tune the drum.
- you can create beating by adjusting the Filter fc and mixing in a VCO, adjusting its fc too
- EG1 has NO SUSTAIN LEVEL. It’s sustain level is always the max (+5V), only the delay, attack and release may be changed. With Attack and Release at 0, it becomes a square pulse, at +5V for as long as you hold the key! It can be routed to the INITIAL GAIN point in the VCA for all-on or Organ sounds. This way, EG2 can be used for something else (with Sustain level at 0 or some non-+5 value). So, EG2 can be circumvented with EG1 acting as a very simple EG.
- With all EG2 controls at 0, nothing happens on a key-down/up event since the sustain level is also 0. On EG1, that is not the case; with all controls at 0 you get the square pulse above, staying high as long as the key is held down.