Hey, so upon watching a video on how to route your modular rack into a matrix brute I noticed the author mentioned the expression jack pathway couldn't exceed +3.3 volts, does this mean any other jack could support -12 from modular rack? Does anyone have experience or info to help me with this? Thanks!
Go to Arturia's website and DL the Matrixbrute manual, and then see page 2. The expression pedal I/Os aren't really supposed to connect to a modular system, but actual pedals. The rest of the I/O should be at normal synth levels.
No, the +/- 12V you're probably thinking of is generally what you find on your power rails. Synth-level signals usually work like this:
Audio: this tends to be +/- 8V peak to peak at max, much of the time, but levels up to +/-10V aren't uncommon.
LFOs: as a rule, this is similar to audio levels except when the signals are unipolar. In that case, you see one of two things: either the voltages swing around a given voltage offset level, or 0V is still the center, but there's no negative voltage swing. This last state is also what you see with audio that's been half-wave rectified in waveshaping/distortion.
EGs: 0 to +8V (or a bit more). Envelopes only swing into negative voltages when inverted, as a rule. Some inverted envelopes can also swing from a given positive offset level down to 0V, as well, depending on application.
Gate/triggers: 0 to +5V is the norm. However, some synths use inverse triggers, such as the Korg MS-20, older Yamaha monosynths, etc. Also, the Moog "S-Trig" bus is normally at +5V until triggered, when it drops to 0V; this is unusual, however, as the Moog "S-Trig" is prone to voltage drops due to connecting too many devices to the trigger bus, which can cause the triggering to fire at unwanted times and it's recognized these days as the 'wrong' way to do this.
Note also that some inputs that normally see only positive-going voltages can have interesting reactions when fed with bipolar voltages, and vice-versa.
Control voltages usually scale upward exponentially from 0V in what's known as a volts-per-octave (often written as 'V/8va') relationship. There are different methods, though, with some (again, Korg and Yamaha) using a linear Hz/V scaling, some older synths (notably EML) using 1/10thV steps with 1.2V/8va, and some using bipolar CVs in a V/8va relationship (Moog).