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M/S Encoder & Decoder Processing Unit

Hey I thought I’d share a custom effect preset:

ms-tweak.unit (39.9 KB)

This would be placed in : /ER-301/v0.4/presets/custom-effect

-OS 0.4.25 required! (it uses the mono source mixer introduced in this version)
-this MUST be loaded on a stereo-linked channel otherwise it won’t work

What it does:
This is a Mid-Side encoder/decoder and processor. For anyone not familiar with M/S processing - it allows you to modify phantom centre (the ‘Mid’) Independent of the ‘stereo’ content (the ‘Sides’). This offers significantly more nuanced control of a stereo mix than using standard stereo effects.

How it Works:
Internally, it’s a 3 step process:

  1. Encode to MS: Converts the incoming stereo signal to Mid and Side elements
  2. Process: Allows you to add independent audio processing to the M and S signals
  3. MS Decode: Reconverts the MS signal back to a regular stereo output.

There is no need to dive into the internals, as everything is on the surface:


M and S faders
These affect corresponding volume levels. You can assign these to external faders such as a 16n or 5v CV source. It’s set so 0-5v is 0 to 1 on the fader. If both are M and S are set to 1, then M and S are at unity and the output of this custom effect will sound identical to the input source. The max can be set to 2 if need be so you can crank up beyond nominal.

This fader isn’t adjustable. Instead, enter this subchain and add any mono effects you want to use to process the “MID” / phantom centre.

This fader isn’t adjustable. Instead, enter this subchain and add any mono effects you want to use to process the “SIDE” / stereo content.

To Test:
Have a stereo source/sample to the left of this custom-effect. If using no external CV, set both M/S faders to 1 as a start. Lower the M fader. All centre content should lower until completely gone at a 0 setting.

Tip: This is a great way to analyze song mixes as you can hear what verbs and stereo fx are used

Tip: You can EQ and compress the M and S separately: It’s the backbone of stereo mastering

It’s best used for modern/traditional mixing: ie: Bass/Kick/Snares/Lead Vocals are centre panned. It’s not intended for super old-school content before engineers knew what to do with stereo (ie: all the drums/bass left and vocals and guitars right etc).

It’s a specific type of processor, but for those who can make use of it, enjoy! :slight_smile:


Bloody hell! Badman ting. I’ll be giving this a spin for sure, thanks for your diligent work Neil lad! :smiley:

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@NeilParfitt AMAZING!! Many many thanks for making this, I’ll give it a spin over the weekend :+1:t2:

Niiiice. I just built a Worng LSMSMSLR, and love it, so will obviously need to try this one out as well. :smiley:

thanks @NeilParfitt, this is simply amazing.
and extremely useful for my Ciat Lonbarde Plumbutter which is a bit “stereo heavy” lol

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Amazing, thank you for sharing this unit. Will download later tonight, can’t wait!

I’m a total novice so excuse me if this is a silly question! Just wondering is there an easy way to split this up so you could say encode into M/S on 1&2 and then send around the rest of the system and then decode back to L/R on 3&4?

Thanks again!

If you open up the custom effect you’ll each segment of the process is a different band or custom effect within, so you can save these as presets and give it a go.

Thank you :pray:

Hi Neil, I have a question. I think it’s just me failing to understand something but I kinda thought that with M and S both at 1 and no processing added we should get the same thing on the unit’s output as we feed to its input, right? It encodes to MS and then decodes to LR. And then we can manipulate the stereo width by playing with M and S levels.
However, in my case it’s seriously reducing stereo width. Here’s a stupid test patch —

Unit bypassed:


Unit on, M=1 S=1:


I’m sure I’m either doing something wrong or not understanding how it is supposed to work.
Thank you!


I may have goofed, as there’s a -3db gain drop on the M * and* S sides of the encoder. Try going into band 2 of the encoder and setting both mixers to 0.

As for the stereo hard pan left right, there’s bleed somehow, but results are as expected when I test it with a song playing through it. Center completely vanished at 0.

My assumption would be a lack of delay compensation so it’s not 100% phase accurate


I screwed it up



I’ll have to investigate a little more


Ok - I’ll repost an updated patch … but I think it’s a summing thing in the Bands unit?

Try this:

  1. create a new custom effect to the left of the MS encoder bands unit

  2. Cut the contents of both bands and paste into the custom effect (should be 4 mixers total

  3. delete the empty LR to MS 2 band

  4. on the surface of MS tweak, go to S FX and reassign the input to the left of the newly created custom effect

  5. go into the M FX subchain and reassign the input to the right of the newly created custom effect

That seems to behave better with hard left / right panned stuff

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Great thanks Neil, and thank you for your tutorials as well, big help!

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Thanks a lot! Will experimentt