How to sidechain without a Bus

Hi. I wonder if there’s a way to set up a plugin like a sidechain stereo compressor without having to create a bus just for that. I know you can send a copy of a signal to any track using the routing grid, but how do you tell Ardour which plugin inputs it should send the audio from a track’s own clips through? (necessary for making the sidechain work without creating additional tracks/buses) This ocurred to me after trying to turn a stereo track into a mono track by discarding the right channel using the “make mono regions” command and then deleting the stereo region and dragging the generated left channel from the editor list instead. After doing this only the Left channel was heard as if I had panned the track all the way to the left. I thought “so you can have clips only feed certain track inputs and not just all of them”, then I read about sidechaining in Ardour and this question came to mind.

Also a really quick question that will be really quick to answer to any Mac user: is the “edit using generic controls” a Linux only feature or can you actually do that with AU plugins as well?

Thank you

"generic editing" of plugins is a cross-platform feature.

Since 5.0 it has not been necessary to use a side-chain in most cases. You can see some screenshots and explanation of this in the 5.0 release notes here (scroll down to "Sidechaining and Pin Connections").

There’s also which shows this for Harrison Mixbus but it works the same in Ardour5 (the whole video is worth watching)

Hey, nice youtube link x42. Indeed he seems to set up the compressor without creating any additional bus or track. More interestingly, he seems to be creating a send from a track to another track, which doesn’t seem possible in v4 as only Buses are listed in the “new aux send” submenu.

Paul, I think I read a post by you from some time ago in which you was telling another beginner that plugins don’t say to the host “hey, here’s a sidechain input so be sure to use it like that” and instead the user was the one who knew and had to hook up the inputs properly. You said this was a limitation of several plugin formats.

In the video it seems that Mixbus/Ardour automatically detects which input is the saidchain and labels it and displays it accordingly. Ben mentions “metadata”, so is this now a standard? do sidechain capable plugins now let the host always know which input is the sidechain? If instead of Zamcomp he’d used SC2 or SC3 would it have worked?

Whatever the case, pin management seems like a truly powerful feature. I cannot imagine the things it will allow people to do now.

But what I’m most glad to hear is that the generic plugin gui works with all supported platforms/plugin formats! It’s a lot of help on low end laptops like mine.

Thank you

Pin management is a new feature of Ardour5.x and not available in 4.7.
The sidechain-sends are automatically created when selecting a side-chain source in the pin-management dialog for convenience, but you can connect any port manually.

The plugin does not need to explicitly tag a port as sidechain input. You can also manually add sidechains and connect the plugins pins to I/O ports. It’s just a few clicks more. In any case SC2 and SC3 LV2 plugins have meanwhile (2016-April-14) been updated to properly tag their respective sidechain inputs. So if you get a recent version of those, it’s the same experience as with zam-comp or Ardour’s bundled a-comp.

The relevant metadata has been in the LV2 specs for a long time, just no host was using it and few plugins tagged their ports properly. A bit of a chicken/egg situation.

PS. Paul is correct regarding LADSPA, Audio Unit and VST. Generic metadata is a feature of LV2 plugins.

It all sounds so good! pin management is really a spot-on feature, I look forward to exploiting it a lot when I try version 5
I also had a listen to the most recent osm podcast in which the pin connections and sidechaining is used with Ardour’s a-comp compressor. He says he wishes the plugin allowed for longer release times to prevent the music from coming back so quickly but he doesn’t actually say what the current limit is. Is it 500 ms like zamcomp or something different? For that matter do all zam based Ardour plugins controls have the same ranges/limits as their zam counterparts or are there differences between them?

hah, that was actually fixed while Spencer made the podcast. The maximum was 500ms and is 2 seconds now (since Ardour 5.4-145, upcoming 5.5), besides it was never a hard limit (advanced users can edit a-comp’s .ttl file and change the maximum; no recompile is needed). So yes the ranges/limits differ compared to upstream zam, but I don’t know the details and would have to compare it. Damien Zammit would know since he wrote both.

Hang on, What did you say? Not only does Ardour 5 come with built in plugins but you can also change any knob’s limits any time you want by simply changing a number in a text file? That’s another spot on feature man! I’ve withheld from asking because I thought I should try them first, but is the plugins manual page gonna be updated to include all this and more information about built in plugins?

About the manual bus input/output configuration, I cannot add a 3 input / 2 output bus. Whether I start by creating a 3/3 bus and deleting one output or by creating a 2/2 (stereo) bus and adding one input, I always end up with 3 inputs and 3 outputs and if I try to delete one output manually I get “This port cannot be removed. Either the first plugin in the track or buss cannot accept the new number of inputs or the last plugin has more outputs” But this doesn’t make sense because I’m just adding the bus and haven’t even added plugins to it! I also get this message if I try with an audio track instead of a bus…

… Wait I think I discovered the trick: it won’t let me remove the output until I add the 3 inputs / 2 outputs sidechain compressor. And if I remove the sidechain compressor the bus goes back to 3 inputs and 3 outputs. Strange but this is no longer the case in Ardour 5 as the release notes says you can add “odd” plugins, Right?

Knob limits are set by metadata obtained from the plugin. In the case of LV2 plugins, that metadata lives in a text file. It is considered “property” of the plugin (and the plugin developers) and is not intended to be adjusted by users under any circumstances. In the case of other plugin formats, it comes from within the plugin binary blob, and cannot be modified in any meaningful way.

You really should move to Ardour 5 :slight_smile: