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Help with Sidechain Compression

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Help with Sidechain Compression

Postby Killheart7 » Tue Sep 22, 2020 10:33 am

Hello! My first post here. Thanks in advance for any help.

So I've just started playing around with sidechain compression for the first time and a question has immediately come to mind. I'll use the classic kick drum and bass guitar combo as an example. When triggering the compression for the bass guitar using a live kick drum recording, the louder hits on the kick drum are going to trigger heavier compression since they will pass the threshold by more than the weaker hits. This is opposite to what I imagine would be optimal, since the heavier hits are going to need less help from the compressor to gain clarity in the mix. Is there any way to achieve greater compression from weaker hits, and less from lighter ones? As it stands, if I set my compression to be optimal and transparent on the stronger hits, I expect the result to be less effective on weaker hits where the ducking actually matters more.

Sorry if this is a common concept. I've read a couple of articles and watched a couple of videos and nobody has mentioned this at all, and I lack any relevant terminology to search for it specifically. Thanks again.
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Re: Help with Sidechain Compression

Postby The Elf » Tue Sep 22, 2020 12:32 pm

If the stronger kick hits were to dip the bass *less* then you would have a louder mix of kick and bass on the stronger kick hits and a quieter mix of kick and bass on the weaker hits. I can imagine this making the low end of your mix sound very lumpy and inconsistent - quite the opposite of what is usually desirable in a mix.

But if you're set on this path...

Create MIDI notes from your kick drum and use these to drive your side-chain (maybe triggering samples from your kick drum track itself). You will be able to play with the velocity of these MIDI notes to control the compressor as you see fit.
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Re: Help with Sidechain Compression

Postby James Perrett » Tue Sep 22, 2020 2:02 pm

Compress the kick before sending it to the bass compressor?
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Re: Help with Sidechain Compression

Postby The Elf » Tue Sep 22, 2020 2:08 pm

James Perrett wrote:Compress the kick before sending it to the bass compressor?
That's a sensible approach generally, since it gives a more consistent result, but the OP here wants to *reverse* the action of the side-chained compressor.

I can imagine a couple of polarity tricks that would achieve it (in addition to my suggestion above), but I can't imagine ever wanting it to work this way.
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Re: Help with Sidechain Compression

Postby desmond » Tue Sep 22, 2020 3:03 pm

The Elf wrote:
James Perrett wrote:Compress the kick before sending it to the bass compressor?
That's a sensible approach generally, since it gives a more consistent result, but the OP here wants to *reverse* the action of the side-chained compressor.

I think he means to even out the sidechained kick by an extra comp *before* it then gets used in the sidechain path, for a more even sidechain response - which would have been my suggestion too.
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Re: Help with Sidechain Compression

Postby The Elf » Tue Sep 22, 2020 3:05 pm

Yes, but none of this would reverse the effect - which is what the OP wants.
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Re: Help with Sidechain Compression

Postby Killheart7 » Tue Sep 22, 2020 9:25 pm

Hey, thanks for the replies so far. Yes, indeed I do want to invert the action of the compressor. It would give a less even overall result, but supposing I'm recording a piece that's intended to be highly dynamic I could imagine this approach getting the mixing benefits of sidechain compression while retaining something closer to the dynamics of the live performance. All of this is academic for now, but I'd love to at least figure out a method to test it for any value.
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Re: Help with Sidechain Compression

Postby CS70 » Wed Sep 23, 2020 12:19 pm

Killheart7 wrote:When triggering the compression for the bass guitar using a live kick drum recording, the louder hits on the kick drum are going to trigger heavier compression since they will pass the threshold by more than the weaker hits.

What matters is at which level the kick exceeds the threshold, not where it peaks... and so long you set the threshold low enough and the attack fast enough, any kick hit will exceed it and the compressor will reduce the bass volume according to the compression ratio.

What theoretically would change is the "hold time" - ie. the time the compressor keeps the level down before starting the release: quieter kicks will go back down below the threshold quicker than louder ones, since they have, so to say, less to fall. So for quieter kicks, the compressor will stop acting earlier (or in other words, start releasing earlier). If the attack is slow enough, quieter kicks might even stop the downward action of the compressor before it's reached the full ratio (that I guess would depend on how the compressor is designed).

True, all this might theoretically leave the bass reduced the same amount for both quiet and loud kick hits (which is what you're worried about)... ending up with louder kicks poking out more.. but gotta say, it's not an issue I've ever encountered much in practice.. kick hits may be peaking slightly differently, but the difference will be very seldom so big that it affects the overall compression action in a noticeable way. and being transients, they are so fast that the "hold" time is very small anyways. Setting attack and release by ear usually works fine unless one of the kick hits is a mistake, and then you simply replace the offending kick transient with a correct instance. And of course the attack and release curve shapes matter, which is why you want the "right" compressor.

In strange cases where this is a real issue, you might want to use a ducking gate instead of a compressor - the only difference being that a gate has a specific "hold" control (and usually linear attack and release, or whereabouts). That's actually is my go-to solution when I want more emphasis on kick or bass.
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