What is the best setup for Parallel Processing within Ardour?

Hey there,

So what is the best arrangement for parallel processing/compression using Ardour?

Here are two I tried, with some notes about each, below:

The one on the left led to an “ambiguous” latency warning, although it seems Ardour (6.9.0) did successfully compensate the latency perfectly somehow (-I guess just because you get the “ambiguous” warning it doesn’t necessarily mean Ardour can’t handle it properly?). For the one on the right I decided to use some Aux Sends which, according to @x42 on this post about routing recommendations, are fully latency compensated.

@x42 also stated this about parallel compression in the comments:

You have two options:

  1. Use a send to the bus with the compressor
  2. Use the effect inline in the mixer-strip via pin-connections (followed [by] a summing plugin). Pin connections and bypasse[s] are also latency compensated.

:point_up: That second option sounds GREAT to me, -as it could literally remove multiple buses each time I want to use parallel processing! But to achieve it, it does require a decent and simple (and preferably free (as in beer (and also freedom (for bonus points)))) summing plugin.

I tried this free one called NCAR, but a single instance of it requires like 15-20% of my CPU(!):
NCAR Free Summing Plugin

So, does anyone have any recommendations for more efficient/simple summing plugins and/or methods for parallel processing that you use?

I would love to understand what methods people are using and which ones are the most efficient within Ardour’s framework!

-Thanks! :grin: :+1:

You don’t need the extra “Plain” bus. You can just use the “Tone Track” itself for that.

it is mainly relevant when recording overdubs.

“ACE Cross Fade” (comes with Ardour) might be one option there


Similar for a stereo track; (note the description of the ACE Cross Fade regarding pinout):


Man, these capabilities are gold.
I’m so glad I spent this evening exploring Ardour some more!
Do you and Paul ever get tired of being freakin’ geniuses?

Thank you!


-It’s funny you mention this, because (embarrassingly) I never understood how someone could solo/monitor only the parallel processed one. That’s because I had previously been using only direct connections, which made that impossible. Now with the Aux Sends, it’s obvious I can just disable the ‘clean’ Aux Send for monitoring only the processed one. :ok_hand:)

Also note that depending on what you are doing, you can duplicate the track and share the playlist between the two tracks (So al edits on one track are copied on the other). You then process one with heavy compression and one with light/no compression, and achieve parallel compression that way, no busses required:)


In exploring using Auxiliary Sends…
-Any reason why a bus wouldn’t show up under “New Aux Send”?


I had a direct connection to this “GM BUS” prior, but then I removed it.
-That ‘history’ might be playing a role here. (And restarting makes no difference.)

Either you already have an aux send to the bus, or making a connection to it would result in a feedback loop. In those cases Ardour does not offer the bus as target.

nope. past state is not relevant.

That makes complete sense, and is a great feature. Unfortunately in my case, neither of those seem to be an issue on close inspection. I undid every relevant connection to help diagnose the problem, and nothing added “GM BUS” to the list, even after a restart.

The only thing that “worked” just now was creating an identical bus with all the same plugins, etc., and then that one appeared on the New Aux Send list no problem.

:thinking: Hmm… I wonder what would be the issue in my case?
It’s not the end of the world. I can use this workaround for these moments.

I usually have to make the buses stereo in order for Ardour to offer them as valid outputs - even if it’s coming from a mono track. I presume that this is because a plugin is splitting the mono source into stereo somewhere along the chain (not sure about that being the reason).

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