Making a plugin ignore / undetect certain frequencies

Hey Y'all What's up. I wonder if there is a way to make a plug-in ignore certain frequencies i choose. For example I'm trying to make the Compressor react only to frequencies above 180hz. If i put an EQ before it, the whole signal is going to be effected, that's not what I'm trying to do. I'm trying to make the Compressor detect only the signals above 180hz as if there is a High Pass filter placed before the Compressor, for example.

Thanks in advance.

The Logic compressor *has* a hi-pass filter for exactly this, in the Side Chain tab.

This filters the sidechain signal which is what the compressor uses to detect how much compression - so rolling off the bass end of the sidechain signal means the compressor doesn't compress so heavily when there is a lot of bass energy.

In addition to what des99 said, you might also want to look more generally into how to use the sidechain (many, but not all, compressors have this functionality). This allows the compressor to react to a separate audio signal, so for example, you could filter/eq/process the side chain signal however you want, and the compressor would react to that, but the signal you would actually hear the compressor acting on would be the unprocessed one.

One of the most common uses for this is filtering out the low end, hence most compressors build this in so you don't have to fiddle with the sidechain yourself.

Hold Up. Duplicating the signal and putting an EQ on it, then muting it and assigning Plug-in's Sidechain to that track would do the job, right?

Actually that's pretty much what i was trying to achieve. But what about Plugins with no Sidechain support? Is there another way to do that?

You could use the right channel to trigger a stereo compressor which then would also attenuate the actual signal in the left channel. However, it would react to that left signal as well.

I don't know of any dynamics processor which does not have a sidechain input.

Hold Up. Duplicating the signal and putting an EQ on it, then muting it and assigning Plug-in's Sidechain to that track would do the job, right?

Yes that's exactly right. Obviously for the particular scenario you mentioned (filtering out the low end), most compressors build that in, so I would follow des99's advice. But if you want to more flexibility, say to filter it a different way, or even to use a completely different signal (I think the kick drum might have been tried once or twice before) you can use the sidechain.

Actually that's pretty much what i was trying to achieve. But what about Plugins with no Sidechain support? Is there another way to do that?

I don't think there's a way to do it without the sidechain, but if there's a trick, I'd be fascinated to know!

I'm asking this for not only Compressors but also other audio processing tools aswell! That's why I'm wondering what to do when there is no Sidechain Input setting.

Where would you need a sidechain input if not for dynamic processors (or a vocoder which isn't a vocoder unless it has a sidechain in...)?

You could use the right channel to trigger a stereo compressor which then would also attenuate the actual signal in the left channel. However, it would react to that left signal as well.

Ooh that's a good idea. Assuming the compressor sums its internal sidechain to mono, I wonder if there would be a way of wrangling it to do what you want by putting the detector signal out of phase and then boosting the frequencies you want attenuated ... ?

I don't know of any dynamics processor which does not have a sidechain input.

Quite a few Waves ones don't (certainly many of the older ones, like Axx, RVox, SSL Compressor). Also Slate VBC.

Assuming the compressor sums its internal sidechain to mono, I wonder if there would be a way of wrangling it to do what you want by putting the detector signal out of phase and then boosting the frequencies you want attenuated ... ?

In theory, yes, although it certainly will be a bitch to set up.

You need to set up the threshold so it reacts correctly to the right side, then also feed a phase inverted copy of the left input into the right input and adjust that signal's level until the compressor does not react anymore to the left side's signal. By that time, I'd have switched to a proper compressor with sidechain. And be done with the entire mix...

Assuming the compressor sums its internal sidechain to mono, I wonder if there would be a way of wrangling it to do what you want by putting the detector signal out of phase and then boosting the frequencies you want attenuated ... ?

In theory, yes, although it certainly will be a bitch to set up.

You need to set up the threshold so it reacts correctly to the right side, then also feed a phase inverted copy of the left input into the right input and adjust that signal's level until the compressor does not react anymore to the left side's signal. By that time, I'd have switched to a proper compressor with sidechain. And be done with the entire mix...

Haha, yes I think it would be a bit of a desperation move

Note that the sidechain filtering filters only the sidechain, which means the entire frequency range of the signal is still processed. If your high frequencies trigger -6 dB of gain reduction, then -6 dB of gain reduction will be applied to your low frequencies as well.

If that's not what you want you may want to look into a frequency splitter. In that case you're truly dividing your signal into two bands of different frequencies, and process only one of the bands. There's on in the Pedalboard. You could build one with EQs in Logic... let us know if that's what you're after?

Yes, although at that point, you might as well use a multiband compressor that's designed for this.

Yes, for compression for sure. But djsnake mentioned wanting to do this for effects other than Compression. I know i've used this with great results for distortion for example, distorting only a portion of the frequency spectrum of an instrument while keeping the other clean.

Yes frequency splitting, but not sidechaining.

Splitting is easy with a couple Multipressors in parallel and soloing single bands there.

Splitting is easy with a couple Multipressors in parallel and soloing single bands there.

Great idea!!

Borrowed it from this forum...

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