What is a matrix mixer in layman’s terms and how can we use it?

Forgive my ignorance, I’m a beginner. I’ve tried my best to research this online, youtube, and the Patch & Tweak book, but there is very little info on this (or perhaps I’m not searching correctly). I’m interested in the Doepfer A-138m Matrix Mixer module and I would like to know how this specific module is used.

• I understand that it has an audio input and output for each of the four channels, but what are knob functions for A, B, C, D?
• What does unipolar and bipolar mean?
• How can I utilize it in a patch with 2 separate sequencers? What will it do? I noticed people patching it with sequencers so that’s why i ask, otherwise I have no idea.
• What is the purpose of a CV mixer and what are different ways it can be used?

If you have any videos or links I could check out as well for more info, I’d appreciate it.

Well, for starters, it's not an audio mixer...but this should explain what's actually going on...

So, you have four inputs which go "across" to the four pots. Now, if you enable the DC offset jumper, you'll have DC offsets on whichever horizontal row isn't connected to a signal via the bottom pots. This lets you set up three (one of them is for the offset) 1-out/3-in mixers which can add that CV to another CV.

Let's say you want to use it with a sequencer. So, what you'd do is to split the CV coming out of the sequencer's 1V/8va output into three identical signals via a mult. You'll have the same signal on inputs 1-3, and row 4 is your offsets. Then, after also setting the matrix mixer in bipolar mode, you'll have four different output channels with the sequencer out PLUS whatever offset you've dialed in. Couple that with a 4-in/1-out sequential switch, and you can then step through matrix outs 1-4 and let the DC offsets be used to transpose whatever pitch CV destination is desired. The nice thing about using this in bipolar mode is that you can also subtract voltages, so if you suddenly need a BIG pitch change either up or down from the sequencer's output, that's easily done.

Where this really gets fun is when you start combining modulation signals. Remember, you've got 4 ins and 4 outs...and if you want "composite" modulation signals, you can send four different modulation sources to the matrix mixer and get four different composite modulation outputs, depending on how you set the pots.

Basically, they're amazing for scrambling up mods and CVs...Jim's sort of the matrix mixer guy here, so hopefully he'll pop in and point out some other uses.

Well, for starters, it's not an audio mixer...but this should explain what's actually going on...

So, you have four inputs which go "across" to the four pots. Now, if you enable the DC offset jumper, you'll have DC offsets on whichever horizontal row isn't connected to a signal via the bottom pots. This lets you set up three (one of them is for the offset) 1-out/3-in mixers which can add that CV to another CV.

Let's say you want to use it with a sequencer. So, what you'd do is to split the CV coming out of the sequencer's 1V/8va output into three identical signals via a mult. You'll have the same signal on inputs 1-3, and row 4 is your offsets. Then, after also setting the matrix mixer in bipolar mode, you'll have four different output channels with the sequencer out PLUS whatever offset you've dialed in. Couple that with a 4-in/1-out sequential switch, and you can then step through matrix outs 1-4 and let the DC offsets be used to transpose whatever pitch CV destination is desired. The nice thing about using this in bipolar mode is that you can also subtract voltages, so if you suddenly need a BIG pitch change either up or down from the sequencer's output, that's easily done.

Thank you so much for your quick reply. Could you please explain what a DC offset is like im a 5 year old lol?

yeah i have no idea what you said, but very interesting lmao. :P

EDITED May 7th 2022, 03:49

DC offsets are voltages which DON'T move (except manually), but which can be added to another voltage via an adder or similar module to change that signal's voltage level.

Going back to the matrix mixer example...let's say you've got a sequencer line that you want to transpose. So, the CV from that would go into one of the matrix inputs. And from there, let's send that over to row #4. Now, with the offset jumper (on the backside of the module) in place, NOT connecting inputs will cause the matrix mixer to have a DC offset signal on...we'll call it input row #2.

So, if you want different pitches, you use different DC offsets and the matrix mixer combines those with the incoming CV. In bipolar mode (pot centers are "0", and you've got positive mixing to the right, negative mixing to the left), you have attenuverter-like functions. Meaning, that if you want to drop the sequencer's pitch by...we'll say an octave...it would look like this:

Sequencer CV -> Matrix input 1
No connection to input 2, which makes that an offset source
Now, using the vertical mixer row 4...turn up "row 4, input pot 1" to full to let the CV in, then adjust "row 4, input pot 2"...which is the DC offset level...so that you now have the same signal, but one octave down. If you send the CV to row 3 now, then raise the input to full but NO offset, this will give you the sequencer CV MINUS the offset. At that point, just use a two-input switch (actually, the best one for the task is Doepfer's A-151, as the input can be switched between 2, 3 and 4 inputs) and then by switching back and forth between row 3 (pure CV) and row 4 (-1v added to CV), you've got that octave jump...you just need to figure out when you want those octave shifts (via the A-151) to happen. DC offsets are very useful for shifting signal levels by exact amounts, in other words.

One other point, though...DC that gets out of the modular CAN be big trouble if you connect the synth to a DC-coupled amp. Speakers don't do well with that...to the point that you can actually set the speaker drivers ON FIRE by sending a big DC signal into the amp...which puts the speaker into "full travel" while majorly overheating the speaker coil. Not good. This is why I tend to insist on output modules that can DC-isolate, as those will NOT pass an accidental DC offset that's made it to the output stage. Plus, they do a good job of stopping trash, noise, etc from getting into the modular by accident from the signal outputs.

That's a decent overview, I think...it's not a concept that verbalizes well; you really need to see what it does hands-on.

EDITED May 7th 2022, 04:14

well a couple of points:

the a-138m can be used for both cv and audio

if you want to use one (or I think more) of the channels as DC offsets - then you need to set the jumper on the back... if you then use jumpered channels with inputs then the normalisation of the dc-offset is broken and the input is used...

what can you use matrix mixers for:

taking n signals and getting n different signals out - this is particularly useful for:

1. mixing and routing audio signals to different outputs (ie effects/filters etc) - parallel processing/4 different mixed waveforms from a single vco etc etc

2. combining and routing modulation inputs to produce more complex modulation outputs - possibly including dc-offsets

3. adding send/return to mixers that don't have send/return - for example send stereo input (channels 1 & 2) to effects module and then return that to (channels 3 & 4) and then mix channels 1/3 & 2/4 to get a wet/dry mix on the channel 3 & 4 outputs)

4. take n sequences and mix them together to make n different sequences - basically the same as point 2 - feed into quantizers to keep everything in tune - use the offset perhaps to change octaves or root notes - this will also work with gates

etc etc etc

EDITED May 7th 2022, 16:03