ACM210X1 Graphical EQ Plug-In for Linux Released

The ACM210X1 Graphical EQ is now available for Linux. Building on the original ACM210, the plug-in is a ten band EQ, with improved de-cramped analogue modelled filters which accurately replicate the equivalent analogue response, without requiring oversampling, or additional latency.


De-cramped Filters:

At commonly used sample rates such as 44100Hz and 48000Hz, conventional digital EQs can cause frequency response cramping as the filter frequency approaches its upper limit. Conventional solutions such as oversampling can be CPU intensive, introducing other artefacts and additional latency. The ACM210X1 uses innovative analogue filter modelling technology to provide a zero latency de-cramped response, accurately replicating that of an equivalent analogue filter without requiring oversampling.



The cramping effect of a conventional EQ can clearly be seen in the following images below as the filter frequency is increased (yellow and red traces). In this instance the shelf slope becomes significantly steeper and the resonant peak becomes narrowed.



The ACM210X1 is available as VST, VST3, CLAP and JACK format plug-ins. Demos are available free to download. A 30% introductory discount is available for a limited time using code D5C39F80 and selecting Add Discount when you purchase.

More information about the ACM210X1 filter technology is also available here


How does it differ from the ACM210?

The ACM210X1 has an extra bandpass filter type, the filter models have been improved - in as much as they are the next iteration of the technology developed for the original ACM210, and the ACM210X1 is available as a CLAP plug-in and standalone application (JACK) in addition to the VST2 and VST3 versions previously.

Is it possible to get this sonogram feature? Sometimes it is practical when looking for resonances to cut.

The EQ sounds good, like any properly implemented digital EQ. That said, I think when looking at products like CraveEq, TDR Nova + SlickEq, ProQ etc… customers in 2023 need a little more than a just a good sounding digital Eq. Features such as the ability to choose mid, side, left, right & stereo per-band are a necessity today, at least for a genuine workhorse Eq. Also, where’s the ability to choose gain range of the filter? For mastering, +-3dB range is more than enough. The 210 has an almost unusable range for this purpose. The GUI resizing is sketchy too. It’s a shame, the plugs sound excellent, but the UX/UI is very poor.

Not sure what I can say to that. I suspect the plug-in resizing is likely a host dependent / OpenGL / X11 / Ardour issue and there’s nothing I can do about that other than suggest you use another host / OS / plugin. If you drag the lower right corner of the plug-in UI in Reaper for example you can smoothly resize it to any dimension you prefer. Just like some of the plug-ins you mention. As for the ranges. I don’t know what you are referring to specifically. You can adjust the boost / cut of any band by up to 18dB. The low-pass / high-pass / band-pass filters are just that, low-pass, high-pass and band-pass which have a gain of unity at, well, unity. Its what they do.

In Reaper, Mixbus or Ardour, it useable - sure, but it’s not a great experience. With a real mouse it’s absolutely fine, but with a trackpad, at least the HP Envy x360 and a T480s, it can feel very clunky. The 210 and 210x are fine in this respect (yet sorely lacking features for a paid workhorse EQ, regardless of whether the filters are zero-latency and correct at Nyquist).

The FC70 and the Pultec EQs are awkward to use on a trackpad, unless you use the scroll-wheel to adjust gain/threshold. You get used to it, but it doesn’t feel great in terms of GUI control, especially when compared to something from Tokyo Dawn Labs or Crave Eq, which are just exemplary. This is subjective, of course, but I suspect most people working daily on audio projects for a living would agree. Regarding the range… it’s about increasing the precision for the operator. ie: I don’t want the maximum and minimum gain to be 18dB in a mastering context, 3 or 6 is much more appropriate to work with for 99.9% of tasks, and allows for more precision when adjusting parameters. A simple selection for gain ranges makes to tool much more usable, for more people. I’m saying this as a customer btw, having purchased your plugins since the Linux DSP offerings, and also as someone who now masters professionally using other digital and analogue tools (I have written a lot of commercial software too, often in large interdisciplinary teams in a variety of languages for more than 15 years). I believe this kind of honest feedback is extremely important to someone building and shipping software. Ultimately, I’d rather have no GUI (eg, airwindows) than a GUI that can slow me down or feel a bit awkward.

I’ve actually started using a Linux box to pitch to my analogue chain - and I find myself using the free ReEQ because it’s a really nice experience, the extra functionality is superb: any band mid, side, left, right and stereo, stereo gain control, independent mid and side gains, ability to set gain ranges etc. It’s just quick to work with and is just a pleasure to use. And it’s free.

I think the overtone / ACMT plugins are superb sonically, I really do, but the GUI and UX would benefit from honestly user feedback and more QA.


Thanks for the clarification.

For plug-ins with rotary controls you can change the operation mode if your host application supports it. For example Reaper allows you to switch between rotary and linear (the operation of which is set out in the plug-in manual(s), and in detail on the product pages / Guide tab) rotary mode actually provides a very elegant way to manage the control resolution, as the control physics means the gearing will adjust as you increase the ‘radius’ of the control motion.

While many engineers are able to mix ‘in the box’ using laptops / notebook computers, you may be making the job of mastering more difficult if you are attempting to do so with a small built-in touch pad as opposed to a conventional mouse / workstation.

Could you consider instructional videos, so that many people would get more out of them. One picture equals 1000 words. The video equals millions

Obviously, I use a real workstation for the bulk of work (Mac and windows) - Linux + Reaper is just an experiment really, which is why it’s being used for pitching duties. You just need to pitch, and maybe use a little Eq. It shouldn’t matter, but I’m using a trackball when I’m at the studio. But, what about if I need to do something when I’m in another place and don’t have a desk setup? On a train? There’s compelling reasons to use a trackpad and in the modern world, a lot of people do work on the move - audio is no exception here.

Also, regarding mouse movement… regardless of whether it’s in the manual, which I have read, it doesn’t feel that good in use. Sorry. Also, dragging the output levels feels really sketchy too, mouse or trackpad, now that I think about it.

Again, this is positive feedback - I like and own most of the plugins… they sound fantastic. But, in terms of GUI and feature set, they are not in the same ballpark as many offerings other from indie developers releasing on Mac and Windows. Which is a shame, because they sound excellent.

As an engineer or product designer, it’s all too easy to say “user error”. It’s much harder to critique the implementation and make meaningful improvements.

Thank you for the feedback. Its not a case of user-error, but some of this is subjective, and I wouldn’t want other potential users to think it reflects a fault with the software specifically. For example the UI design has been a deliberate and conscious move away from photo-realistic plug-ins. That’s a stylistic choice which may or may not suit your preference. In terms of UX you make some useful points and while we all increasingly often have to work in non-ideal situations (or at inconvenient times, as I write this late on a Sunday afternoon…), I think its not necessarily a fair reflection on the plug-in if you think that using it to master audio ‘On a train’ might be slightly less than ideal.

Fair points indeed, but I frequently work on my laptop in hotels and take my Prism Lyra + LCD4s with me. It’s certainly possible to work on the go. Mostly it’s for editing and a bit of restoration, but I’ve mastered more than a handful of things outside the studio on that rig since 2020 - and it made it to release without getting anyone complaining.

If truth be told, I love the sound of your plugs and just want them to be the best they can be - if only for selfish reasons (like using Linux exclusively for the whole process, home or away). I also think the new non-photo GUI look great - really clean and modern, easy on the eyes, too. I’m just not sold on the knob behaviour, but am “used to it”.

The 210x I genuinely believe would benefit enormously from:

  • m/s/l/r/stereo operation, per-band
  • a “range” control with +/- 3,6,9,12,18 options
  • independent m / s gains

Also, a new plugin idea: you have the FC70 - it sounds lovely and has a very forgiving action. If you split that into 3 bands, as-per PSP OldTimer MB, that would be a monster. The FC70’s action sounds nicer to my ears than OldTimer or MDE compressors, and would offer something not available yet for the Linux platform.

If you need to make fine controlled adjustments on the ACM210X1 you can zoom the display using the scroll-wheel. This is in effect the same as changing the ranges as you suggest. It may not be exactly the feature you are looking for, but it can be useful for making more precise changes.

For example: Mouse over the area you are interested in on any unused area of the EQ graph and scroll-wheel to zoom in or out. You can also click anywhere on the graph and drag up / down / left / right to bring things into view. As you move any marker points the viewable area will scroll automatically to accommodate them, as you might expect.

That’s an interesting suggestion, but to be fair I genuinely think that all the plug-ins already offer something not [otherwise] available for the Linux platform.

To contextualise the issues with the graphical EQ, I don’t know of any other EQ for Linux which provides zero latency de-cramped filters for all filter types (including high-pass, low-pass, and HF / LF shelf) - and it’s important to remember that the ACM210X1 gives you a genuine WYSIWYG - What You See Is What You Get - display (its literally powered from the same coefficients that drive the filters), whereas some others can, and do show you an ideal response while the processing may do something less ideal. It also does this without requiring oversampling, so you get zero latency, no pre-ringing or other artefacts and more CPU available for other less economical plug-ins.
And for anyone who thinks or has been told that de-cramping (especially shelving) filters doesn’t matter, it can be seen from the measured example graphs, that though it happens towards the upper frequency range, even in the case of shelving EQs the effect will extend down into the audible mid-range with modest bandwidth / Q settings. Which is something to consider.
The irony is that a huge of amount of design effort goes into things which, if done correctly, you shouldn’t even be aware of - and might rightly assume all plug-ins do - but this is not always the case.


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