Side-chain : only 128 bus ?

[cmbourget]

I left Pro Tools two years ago for Nuendo and a first Atmos project. I'm coming back to Pro Tools (Ultimate) for a second one. But I'm a bit lost on the question of BUS for the side-chain.

I try to place a Pro Q4 Fab-filter as an external side-chain. It's on a 7.1.2 track. I try to indicate the External Key to Pro Tools, and all I see only, in the BUS list, 128 BUS, i.e. the first series of BUSes. Now, for my side-chains, I want to use the buses beyond the first 128.

Am I missing something?

Update: ok, I understand that the side-chain can only receive mono or stereo BUS. Is this true?

[LDS]

Originally Posted by cmbourget

I left Pro Tools two years ago for Nuendo and a first Atmos project. I'm coming back to Pro Tools (Ultimate) for a second one. But I'm a bit lost on the question of BUS for the side-chain.

I try to place a Pro Q4 Fab-filter as an external side-chain. It's on a 7.1.2 track. I try to indicate the External Key to Pro Tools, and all I see only, in the BUS list, 128 BUS, i.e. the first series of BUSes. Now, for my side-chains, I want to use the buses beyond the first 128.

Am I missing something?

Update: ok, I understand that the side-chain can only receive mono or stereo BUS. Is this true?

VST3 is the only plugin format that supports multichannel side-chaining IIRC. Even then, it is dependent on the coding of the plugin itself rather than something intrinsic in the format.

I'm always curious about these posts that pop up once a year or so. Are you actually sending multi-channel sidechain audio to Pro Q4 and using it to trigger channels independently? I used to do something similar with a Smart C1 in dual mono mode, but realised the preceived added width and space was really just the destruction of a coherent stereo field. Perhaps the effect is minimised due to the move from phantom center images to a point source system?

[cmbourget]

I don't know how well I can explain it in English, but it's pretty standard (or I don't quite understand your question). It's ducking. I don't know if I'm being too simple.

I have 4 main groups, which actually end in beds. Narration (which could be Dialogue), Sound effects (foley), Ambience, Music. I do as I do in stereo (or almost, as the needs are different due to a different space): I choose one or two segments of voice frequencies (narration) for which the music, for example, if there is voice, must recede a little, by a few decibels. Pro Q 4 (or 3) lets you choose at which points in the immersive space, on the signal reception side (in this case, the music), this should happen.

Let me know if you're satisfied with my answer or if I'm missing something.

P.S. And thanks for the info on VST3, I didn't know because it was transparent in Nuendo. I imagine there's an equivalent method in Pro Tools, or a detour. I see that if I create an LCR BUS by requesting subpaths, I have three monos. I can attach the S-C, when it comes to protecting the narration, in the central monitor, to this mono monitor. I don't know if that will work. But if I want the music (according to my example) to recede on certain frequencies in front of the sound effects, for example, when it would be on the rears and pitches, what do I do? I have to figure it out. That said, I'm surrounded by sound engineers, so I'll be asking the question this week.

[LDS]

At least to me, the premise of multi-channel side-chaining is to create processing that is side-chain-source-specific. As an example, dialogue that gets panned from the centre channel, right around the room perimeter, and back to the centre channel. Using a multi-channel side-chain with Pro Q4 set to discrete, multi-channel processing, the ducking would only ever happen in the music in the channel that the dialogue appears in - the ducking pans through the Pro Q4 processor channels in the same way the dialogue does in the room. Is that what you're chasing? It isn't really possible in Pro Tools without changes to the AAX format unfortunately.

If all you are trying to do is duck your L/C/R music channels based on the side-chain, it seems entirely possible with mono side-chains? Maybe this will help?

Pro Tools approaches busses in a few difference ways;

- If you have Routing Coefficients set to downmix in your preferences, sending a 7.1.2 channel to a mono send will fold it all down. All 10 channels will appear in the mono send, and thus in the side-chain signal.

- If you create a 7.1.2 channel bus with default subpaths, you can send a full 7.1.2 channel to a 7.1.2 bus, then if you can also choose only the centre channel of that bus as your side-chain signal if you only want your centre channel dialogue to be triggering the processing.

Pro Tools can also approach plugins in a few ways;

- If you choose a multi-channel plugin for a 7.1.2 channel, the channel functionality becomes very dependant on the design of the plugin. In the case of Pro Q3 and Pro Q4, you can assign EQ curves straight to individual channels or channel groups. It is possible to create an EQ curve just for L/C/R, and assign your side-chain only to effect it.

- If you choose a multi-mono plugin for a 7.1.2 channel, you will effectively get 10 mono plugin in one. In the top right corner of the plugin window, there is link and channel selection buttons.

[cmbourget]

Many thanks LDS, you're a great help. I think the description in your first paragraph is what I was looking for and that you understood very well. But I'm in Pro Tools with AAX, (not in Nuendo with VST3) and I must be forgetting this optic. Another Daw, another logic.

Honestly, I didn't know about these Routing and Downmix Coefficients options. I chose to split the signals, i.e. to distribute them. In fact, these options only refer to side and rear signals. According to what you say, which seems to correspond basically to the Modern configuration instead of Classic, the elevations are also considered (although there are no specific options for this). In any case, I prefer this method to that of manually selected secondary channels.

As for the plugins, as I said, I do know the placement options for Pro Q3 and Q4. Thanks for confirming. In the case of this (admittedly extraordinary) plugin, which I use mainly for the ducking we're talking about, I'll be using these options. For other plugins that don't offer these same capabilities, I'll go through multimonos (I need to get to know it because Nuendo doesn't have this - although it's been requested for a long time).

Thanks again for the clarification.