How to achieve multiband processing?

I’m a new Ardour user and I’m loving it, thanks to all the devs, your work is highly appreciated. Hope some day I’ll be able to contribute to it!

Anyway, coming from other DAWs, I’m trying to understand how things work and how I can do what I want.
What are the possibilities I have for splitting a track processing in two or more parallel processing chains?
For example I have an Audio/MIDI track and want to process the lows, mids and highs in different ways, how can I achieve such a result?
What I thought at first was using three sends to three different busses with an EQ on each to split the spectrum. It works but I was wondering if there is a more Ardour way to have the same result.
Thanks in advance for your help.

Duplicate the region onto two more tracks in the editing window.
There is a key/mouse combination for this. Middle button drag moves the region up or down without any sideways movement, and (I think) holding the Ctrl key down while you do that will make a copy on the new track.
Then set up your filters and processing on each track as required…

The simplest way is to create 2 additional tracks. Then use the “p” button to make them all use (share) the same playlist. That way, you can edit in any of the 3 tracks, and it will propagate into the other 2, but they can all have independent processing.


I expect the hard part is to find a crossover-filter plugin that splits the signal in a way that when re-combined result in a flat frequency spectrum with linear phase.

From the top of my head, I would not know a standalone plugin that offers this. zita-lrx comes to mind, but that’s a jack app.

What are you using?

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Actually I didn’t think about it. On Ableton I was using Multiband Dynamics that is a multiband compressor, any advice would be welcome.

That very much depends on the EQ of Filter, but usually yes, also the phase won’t be linear over the whole spectrum with default HP/LP filters. Designing good cross-over filters is hard.

You can check with a null-test: Create a session with three mono busses:

  • Feed all with the same white noise (or same signal)
  • Polarity invert the first bus
  • add a HP filter on the 2nd bus
  • add a LP filter on the 3rd bus

If all goes well that sums to zero (silence) on the master bus.

It very much depends what your goal is:
If you’re mixing/mastering, phase-smearing will be a big issue.
But if you’re sculpting synth sounds with this multiband processing, it can be a welcome artifact.


I was just going to ask: Why not use a plugin that does this properly internally?

On GNU/Linux, if you want to use free-software, I’d recommend either LSP’s multband suite [1] or ZaMultiComp [2]. If you’re open to non-free/proprietary software there’s a lot out there. e.g. Harrison’s XT-MC [3,4] comes with Ardour binaries from


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First I want to thank you for the time you’re taking to reply to me, you made me realize something I didn’t think about before and I’m really thankful.
I will check out the names you gave me but the problem with all-in-one multiband processing plugins is that you have to use their internal effects and cannot use other plugins so I find that a bit limitating.
As per what you said in the other comment though you’re right, I am using this technique mostly to create synth sounds so it’s not a huge issue.

Edit: nevermind I checked out LSP and they have a multiband compressor so you were suggesting me to use that as I was doing in Ableton, I thought you were suggesting me all-in-one processors. Thanks again.

You can use the Cross Over Plugins from (“X-Over”). Therefore you have to set the Pin mode of your Track to Flexible E/A. Than you can add the X-Over Plugin at the end of the Plugin Chain. Now you have outputs for each band that you can route to different buses or audio tracks.

I know that the Ardour team advises against using Calf plugins. I also cannot say much about the quality of Calfs cross-over algorithm. For me, it has worked well so far.

Does anyone know of any other cross-over plugins under Linux?


I think you probably are looking for it:

A Unfa tutorial. At 24:30 minutes he shows how to split the audio from a MIDI synth in three bands and process them.


Yeah, that’s kind of what I meant. Unfa does it with the help of the pins in one track. That’s great.

Didn’t know they advise against them, do you know why? They look good to me.

That’s exactly what I was searching for, thanks a lot!
Also Ardour is really awesome.

Calf plugins are known to some times prevent loading of Ardour sessions etc. I’ve been following this forum for many years and many reports of strange problems users have with their sessions stem from calf - plugins. Because of this I don’t use these plugins and never had problems like these.

Not only do they prevent projects from loading, but if you try to automate any calf plugin parameters, it’ll usually get all glitchy sounding.
Also, I cannot recommend Harrison’s Multiband Compressor plugin enough!! I have a hardware multiband compressor, but when it’s already in use, I am glad to fall back on Harrison’s. They do great work.

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Calf’s cross-over (and calf-multiband compressor) do introduce phasing issues. In fact Calf makes the same mistake as the OP, using default EQ as cross-over filters. This results in notching out frequencies and introduces phase shifts.

What’s worse, is the Calf-GUI does not show this and makes you believe that it’s flat and looks fine.
It’s easily measured however using a spectrum analyzer[1], or in case of calf multiband compressor using Ardour’s built-in plugin transient analysis [2].

If you want phase-smearing (abuse the plugin like unfa does for sculpting sounds) this is fine.

However for mixing or mastering those plugins will cause significant issues that proper multiband FX do not have.

Just be aware that what you see in Calf’s GUI is not what you hear. This may be an issue if you use those plugins to learn, and you then have to unlearn for all other x-overs. However if you’re aware of the issues you may use them to your advantage.

[1] White noise passed through calf x-over, the spectrum is supposed to be flat.

[2] Calf Multiband compressor with default settings, and plugin transient analysis below.
The phase response (red line), as well as the frequency response (white line) should be flat.


I will reitterate what @x42 says from a different less technical standpoint. The phase issues in Calf’s EQs are audible. I avoid them for that reason along with the technical issues they can account for as well. It is sad as it would be a nice introductory suite of plugins and I have heard some of their stuff like the compressors sound good, but there are much better choices for EQ and multiband processing.


EDIT: Sorry it thought I hit post WAY to early in the post


LSP Multiband processing plugins also solve the phase distortion problem


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