Of inserts, busses and multipe plugin instances

Getting Stuff Done How do I .... ?
#1

Hi,
I’m trying out a new workflow and I’m running up against a problem that I think may be indicactive of me thinking the wrong way.

I have two vocal tracks that I want to send through a shared EQ. Each track should only get back from that EQ the (processed) signal that was sent from that track. Basically I don’t want to put an EQ with the same settings on both tracks.

My solution:

  • Add a BUS, called ‘EQ-my-vocal’

  • Create 4 audio ins / outs on the bus

  • Add my splended EQ plugin on that bus and tweak it to taste

  • In the ‘pinout settings’ of the EQ plugin, create 2 instances of the plugin

  • Instance 1 gets audio 1/2 io

  • Instance 2 gets audio 3/4 io

  • On each of my vocal tracks, create an insert

  • Route the Vocal 1’s insert L/R OUT to ‘EQ-my-vocal’ IN 1/2

  • Route Vocal 1’s insert L/R IN to ‘EQ-my-vocal’ OUT 1/2

  • Route the Vocal 2’s insert L/R OUT to ‘EQ-my-vocal’ IN 3/4

  • Route Vocal 2’s insert L/R IN to ‘EQ-my-vocal’ OUT 3/4

Now this seems to work, audio-wise. Each track gets the correct processed audio back from my EQ bus and I only have to change one set of plugin settings if I want to tweak the EQ for both tracks.

The problem is that Ardour’s feedback light starts blinking as soon as I connect the output of the bus back into the send that it is recieving. I can’t hear any feedback, but the light blinks nonetheless.

I also tried this with a simpler setup, with a ‘normal’ stereo bus and an insert on a stereo track. As soon as I go Track -> insert-out -> Bus -> insert-in -> Track the feedback light starts blinking away. I assume this is because Ardour is seeing the (insert)OUT->(bus)IN ->(bus)OUT->insert(IN) and incorrectly identifying this as a feedback loop.

Is this just a bug / limitation in ardour? Or am I barking up the wrong tree?

#2

That is correct.

You can’t “insert” a Bus into an Ardour track (or vice versa). That results in circular dependencies.

Tracks and Busses are monolithic. SIgnal-flow through a track cannot be interrupted in the middle.
For your case: Ardour would have to stop processing the Track at the “insert-out”. Then process the bus, and after that’s done continue with the Track. That’s not possible.

The Bus depends on data from the track, and the Track depends on data from the Bus. So Ardour indicates a feedback cycle.

You could either use Track -> Bus {EQ} -> more busses -> master.

Or simply copy EQ settings via drag/drop (if you drag/drop a plugin icon to another plugin of the same type on another mixer-strip, the state is copied).

#3

Fair enough, that makes sense. I take it that inserts should only be used to send / return to external processors, whether software or hardware?

Thank you for your reply, and for your suggestions. I didn’t know about the drag / dropping plugin settings.

#4

In practice what bad thing could happen if I “insert” an audio Bus into a track?
Besides the blinking Feedback indicator.

#5

Ardour allows you to temporarily create circular dependencies while making connections, but next time you start Ardour, there is no valid process graph, and Ardour will remain silent.

#6

Thank you for your reply, Robin.

Ardour 8 actually works with it after restarting it.
Bus Inserted to Bus seems to works flawlessly.

So this limitation seems to be just a philosophical or ideological one and not a real one. Or is it somehow a real one?

With a similitude it is like Ardour knows English and there is nothing she can do with German, but if addressed in German she knows German perfectly.

Anyways if I wire the insert’s send/output to a Jack-Carla passthrough solution and then set that passthough as the input of the Bus and then I set the Bus out to the insert’s return/input everything works and also there is no indication of Feedback problems, while everything is the same.

So actually it works, works correctly, and why can’t we use it directly without a round of external bypass or without the Feedback indicator blinking?