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Compression on Stereo Field

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Compression on Stereo Field

Postby Slayerstation » Thu Jun 13, 2019 1:22 pm

Hey there,

I have a question about if compression affects the stereo field

Thank you for responding and greetings from The Netherlands
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Re: Compression on Stereo Field

Postby Slayerstation » Thu Jun 13, 2019 3:58 pm

I meant how compression affects the stereo field
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Re: Compression on Stereo Field

Postby desmond » Thu Jun 13, 2019 4:06 pm

A stereo compressor, in link mode, compresses both channels the same, to stereo width or the panning of the signal is not changed by the compression process.

If you run a dual-mono compressor, or a stereo compressor when the channels are unlinked, this can affect the stereo image, as each channel can be compressed differently (due to differing sidechain levels detected), so the image can be shifted (ie, if the left signal is reduced more than the right, the signal will seem to move to the right.

Both are valid approaches, and duel mono can be useful sometimes, but you have to watch for the image shifting because of this effect.

You can also do Mid/Side compression, which can affect the stereo width, depending on how you use it.

What is it you are trying to do?
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Re: Compression on Stereo Field

Postby Slayerstation » Thu Jun 13, 2019 4:20 pm

I want to sidechain the kick to a side compressor on some leads
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Re: Compression on Stereo Field

Postby desmond » Thu Jun 13, 2019 4:36 pm

Slayerstation wrote:I want to sidechain the kick to a side compressor on some leads

For what purpose? What are you trying to do?

If you are just ducking the leads with the kick for that EDM pumping effect, then as long as you use a stereo linked compressor, the stereo width won't be affected at all, just the volume.
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Re: Compression on Stereo Field

Postby Hugh Robjohns » Thu Jun 13, 2019 4:48 pm

quote="Slayerstation"]I have a question about if compression affects the stereo field[/quote]

Not as long as you use a dedicated stereo compressor, or the stereo-link facility of a dual-mono (or two separate but linked mono) compressor(s).

If the compressors on each channel of a stereo signal are not linked, and there's a loud transient only on one side, that channel will apply gain-reduction and reduce the level. However, any sound element that was supposed to be central in the stereo image is only central because it has equal levels in the two channels. If one channel is suddenly made quieter by the gain reduction applied by a compressor, the (originally) central sound will appear to move over towards the other (unaffected) channel.

So the stereo image will wander about in un-linked compressors. The speed at which they move is dependent on the compressor's attack and release time constants, and the amount of travel is dependent on the amount of gain-reduction being applied.

The simple solution to avoid this effect is to link the side-chains of the two compressors together so that whatever amount of gain-reduction one compressor decides to impose (whichever wants to apply the most gain-reduction) , the other will do exactly the same regardless of what's going on in its own channel, and thus the stereo image remains stable. Usually, the compressors settings should be the same for ratio, threshold, and time constants, of course.

Alternatively, if link-able compressors aren't available, a generally acceptable bodge is to convert the stereo signal to Mid-Sides format and then process those two channels with independent compressors before converting the output back to left-right. The compressors settings should (usually) be the same for ratio, threshold, and time constants, again.

In this configuration case, there is still stereo image movement, but it manifests as changes of width rather than left-right shifts, and width changes are much less noticeable to most listeners.

Here's an extreme demonstration of what can happen with un-linked compressors!

http://www.robjohns.org.uk/unlinked%20compressor%20dem.mp3
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Re: Compression on Stereo Field

Postby Slayerstation » Thu Jun 13, 2019 4:50 pm

Making the sound widen up after the kick has hit. You hear that often in future bass tracks
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Re: Compression on Stereo Field

Postby Slayerstation » Thu Jun 13, 2019 4:55 pm

Thank you Hugh,

That creates a very interesting effect. And you made me much wiser about the topic. Thanks for your time and advice. That is much appreciated :D
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Re: Compression on Stereo Field

Postby Hugh Robjohns » Thu Jun 13, 2019 5:00 pm

Slayerstation wrote:I want to sidechain the kick to a side compressor on some leads

Are you saying you are processing a stereo signal in Mid-Sides format?

If you are, and the kick drum signal is being fed into the side-chain input of the Sides compressor, only, then it will cause the Sides compressor to introduce more gain reduction on the kick drum hits, reducing the level of the Sides signal on the beats.

Lower Sides level means the decoded stereo signal image will be narrower -- more mono -- on the kick drum hits, and then open out wider again between the beats, assuming the release/recovery time is fast enough.

But if the Mid and Sides compressor are linked then it will just pull the overall level down on the kick drum hits, for that pumping effect, without disturbing the stereo image at all.

Hope that helps.

H
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