Fat Comp & Ez Comp custom unit (donationware)

Hello dear fellow 301ers, its quite a long time since my last custom unit.
as you might know we are currently in lockdown in italy, i live in Lombardia, the area that has the most infections. My job is teaching (i’m a freelance working in two different schools and also giving private tuition), schools were closed 3 weeks before the lockdown so, without panicking, i must admit this is a very difficult time money-wise.
Therefore for the first time i’m asking you to kindly make a donation (doesn’t matter how much) if you like my contributions and would like to help a fellow sound designer in times of need :slight_smile:
you can use paypal and send me whatever amount at
a big hug in advance to all of you.

here we go…
i wanted to create a compressor with most of the features that make it useful and versatile. i ended up with two versions based on two slightly different approaches. the cool thing is that both have a sidechain filter and on both you can use an external sidechain.
The sidechain filter is an high pass filter and works for the normal signal and the external sidechain as well. it helps cleaning up the analyzed signal from low frequencies that might keep the amount of gain reduction high for too much time, it is key to the proper use of a compressor especially when used on drum parts or with drums as external sidechain.

Fat Comp
this one uses a comparator to drive an ADSR envelope on a VCA.
it has a threshold, ratio and time parameters. you can dial in an hp filter on the sidechain signal (internal or external): please keep in mind that the high pass filter WILL NOT affect the sound you hear, only the signal driving the gain reduction.
fatcomp1 fatcomp2


  • threshold: decrease it for more compression, this sets the level above which the compressor starts working
  • ratio: increase it for more compression, this sets the factor of gain reduction. 1x means no compression (1:1 ratio)
  • attack: how fast the compressor reacts to peaks in signal level.
  • release: how fast the compressor stops working (reducing gain)
  • key hp: frequency of the high pass filter on the sidechain (key) signal
  • ext key: a toggle button, when on it engages the external sidechain
  • key in: input for external sidechain (key). enter the subchain and assign an input or insert a unit then enable ext key toggle button

requires: Accents
cpu: about 10%
download Fat Comp: fat comp.unit (26.3 KB)

Ez Comp


Same as Fat Comp but this one is simpler, it has no threshold control and it is based on an envelope follower. it still has sidechain filtering and external sidechain.
controls are the same as Fat Comp but there is no threshold control

requires: nothing
cpu: about 9%
download Ez Comp: ez comp.unit (22.3 KB)


Very cool , looking forward to checking it out. And I see nothing wrong with donation ware ( hopefully that topic doesn’t spin out of control in here like last time).


Thanks Hyena and I for one am happy to help.


Hey @hyena thanks for your contributing MORE useful tools. Good to see you’re well. I think your move here with the ‘first’ donationware object is timely considering the advances in the firmware for the 301. I look forward to seeing and supporting more of your work in the future.

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Hope my small contribution helps out a little. Take care, and let us know if you have more donationware for us :wink:

I will check out the unit asap!

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:open_mouth: i’m overwhelmed! thanks everybody, you’ve all been way TOO generous!!!
you don’t know how much i appreciate your support <3
here we are doing fine, i for one am more than a bit critic of how the establishment here is handling the situation, but its a very complex and deep topic that i’m afraid will touch the lives of all of us in the future (how society will change and how people will react on the long term is a big big question mark).
i’m spending my time doing some online classes and studying a lot (harmony, music theory and guitar other than the usual technical\synthsis\sound design topics), reading a lot (the Chatelet history of philosophy, i’m on Aristoteles right now :expressionless: ) trying to avoid the media\information overconsumpion that i think only triggers anxiety.

again, massive thanks to all of you for your warm support, i love this community!!!


It’s a hard time out there, the best way we get through it is together!


Wow thanks, seems a nice nice custom addition! I’ll try it today…
Daje Lombardia :black_heart:

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Just coming of out of my lurker shell but I know lots of us have been wanting a premade compressor. I also fully support the donationware idea, since it lets us remunerate people for their work without the expectation of full support, etc. If more people developing units here were to supply payment info I would definitely chip in. Nice work!

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heartfelt thanks!
i have some ideas to test to further develop the Fat Comp unit.
in fact the goal i have in mind is to get totally rid of the adsr and use something that model an actual analog compressor. i’m sketching a lot on paper to try to find suitable solutions :slight_smile: this is one of the things i like most of the er-301: it pushes you to think more, to use logic, to find solutions! as i stated many times before it is the best platform i’ve ever worked with, mostly because of how coherent the internal organization is, of how simple and effective the gui is. i have to study lua sooner or later and go down into the rabbit hole of coding stuff for it!!!
again, thanks everybody for your generosity. it absolutely exceeded my expectations!!!

p.s.: i forgot to ask this time but all feedback is welcome and deeply appreciated! harsh criticism included!!!

Instead of an adsr I bet a slew limiter on the threshold detector would get the job done pretty naturally.

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thanks for the input!
ez comp uses an envelope follower, fat comp an adsr driven by the comparator. i might try the slew limiter but this way you only have one time control, not two (attack and release)

Ah yea I forgot it only had one time control, so it’s use an adsr or two slew limiters (one up, one down). I guess it’s functionally the same. One other thing I was thinking about was using a bump scanner as the threshold detector, but not 100% sure how that would really work.

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Can’t you use two slew limiters and set one to positive slewing and one to negative slewing?


hey hyena, am just starting to get into music production more deeply and am learning about compression with drums. for now i’m just trying to utilise a ducking sidechain for my kick but am a bit confuse by the layout. i’m just using some ambient pads as a test but i cant get it to duck when the kick comes. which part of the unit do I need to assign my kick to get the pad to duck?

hope you can help, stay healthy


Hello and thanks for trying out my units!
so, the workflow is this:
you have your pad (i don’t know if its already made on the er-301 or an external signal, if its an external signal you just plug it in one of the 4 inputs then select the chain you want to use, click on the input header of the chain and select your input) on a chain, insert one of the two compressors just after the pad.
then plug your kick signal into one of the four inputs of the er-301 (lets say its input 4),
now go to the “key in” slider, click on it to enter its subchain, go on the header at the left of the subchain, click on it and select the input where your kick is (in this example input 4).
the gain is already set , so now you just have to click on the “ext key” button to enable external sidechain.
here you go! now set the compressor’s parameters and you are good to go!

from the user manual:
key in : input for external sidechain (key). enter the subchain and assign an input or insert a unit then enable ext key toggle button

tell me if now its clear and if you achieve the results you were aiming for please!
and any feedback is always welcome!


please keep in mind that even if it looks like a slider, the “key in” parameter actually acts as an INPUT so you don’t have to touch the slider, nor touch its “gain” and “bias” parameters on the small display. it’s already prepared to do its job

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Thanks a lot, really appreciate the simplification. just need to familiarise myself with the audio terms. everythings working great. amazing unit!

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really glad to hear it mate! looking forward to listen to some of your er-301 based tracks!

i have to re-state my gratitude for all donations,my friends! they’ve been OVERWHELMING!!! and helped a lot! thank you <3 !!!