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What is a "resonance" peak used for, why is it so common at the cutoff frequency of filters?

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What is a "resonance" peak used for, why is it so common at the cutoff frequency of filters?

Postby alexis » Sun Mar 31, 2013 3:18 pm

Hi - Noticed for a long while that some cutoff filters have a resonance peak at the cutoff frequency. Listening to a cutoff filter with and without I can hear a difference, but what I don't understand is ... what do people like about it that makes it so prevalent?

I figure since it is so frequently available (even as a default) on so many filters it must be an extremely desirable feature of a filtered signal to have a resonance peak at the cutoff frequency, but I have no idea why by just listening to it.

Thanks for any thoughts!
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Re: What is a "resonance" peak used for, why is it so common at the cutoff frequency of filters?

Postby Mixedup » Sun Mar 31, 2013 9:07 pm

It's just a little narrow boost next to the cutoff frequency. It effectively emphasises a note as well as filtering frequencies away. It's common with synths to sweep an LP filter along in the frequency domain, either linked to the note played, or via automation — or midi controllers or knob twiddling in the old days! Try it... you'll recognise the effect, and then probably start over-using it!
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Re: What is a "resonance" peak used for, why is it so common at the cutoff frequency of filters?

Postby alexis » Sun Mar 31, 2013 9:55 pm

Mixedup wrote:It's just a little narrow boost next to the cutoff frequency. It effectively emphasises a note as well as filtering frequencies away. It's common with synths to sweep an LP filter along in the frequency domain, either linked to the note played, or via automation — or midi controllers or knob twiddling in the old days! Try it... you'll recognise the effect, and then probably start over-using it!

Thanks again, Mixedup! I see what it is visually, as it is one of the four or so presets in the Cubase HPFs (and also it's a control in the GVST HPF that you suggested ... thanks for that tip)!

Also, I somehow kind of knew it was commonly used in synths (ELP, etc.). But as I don't use that kind of synth, mainly just audio in for vox and rhythm sticks, piano and various "old-fashioned" instruments like trumpets, drums, and bass via my Motif or VSTi's - I couldn't tell if it was like a bell on a chair for my kind of work, or whether there was a certain kind of situation I should try it.

As I mentioned initially, it didn't really do anything magical for me when I tried it on voice, and certainly not on acoustic piano.

Would I be right if I wondered whether a resonance peak on a HPF isn't that generally used for the kind of music I am making? Or (I can take it ), way off base with that generalization?

Thanks!
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Re: What is a "resonance" peak used for, why is it so common at the cutoff frequency of filters?

Postby Mixedup » Sun Mar 31, 2013 10:06 pm

Depends what it is you're trying to do. I'll sometimes use it on a kick drum, just to give a bump at a certain frequency — draw out a certain note to fit the song, etc. Sometimes, just to change the slope of the top of the filter before it goes into its normal x dB/octave cut. It's no different from using a conventional narrow bell boost alongside the HPF, really, but I like having the two things sweepable with one freq control — less hassle that way if I want to change the frequency. Probably more common on LP filters — it really grabs attention when you move the frequency down/up, without having to change the note or anything complicated like that Try using a filter like that on some noise from a synth or test generator, and you'll see what I mean — that howling wind sort of effect!

If I'm honest, though, I use all of the above far less than I used to!
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Re: What is a "resonance" peak used for, why is it so common at the cutoff frequency of filters?

Postby BJG145 » Sun Mar 31, 2013 10:07 pm

alexis wrote:...it must be an extremely desirable feature of a filtered signal to have a resonance peak at the cutoff frequency, but I have no idea why...


I don't get why resonance crops up in EQs either, and it's not particularly easy to turn up info on where it came from, or why or how people use it...

Probably originated as a result of some electronics jiggery-pokery and people then decided to model this "character".
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Re: What is a "resonance" peak used for, why is it so common at the cutoff frequency of filters?

Postby alexis » Mon Apr 01, 2013 2:52 am


Very nice, hollowsun, thanks!

Reading it, it seems like it is something maybe I'd best put aside for now, concentrating more on my basic mixing package than trying to get too busy with advanced mixing techniques like this (besides which, I shudder to think what my voice would sound like if it "self-oscillated" :-o. But I will probably at least be more likely to give a quick listen/try now and then as a result of all this.

Thanks again!
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Re: What is a "resonance" peak used for, why is it so common at the cutoff frequency of filters?

Postby The Elf » Mon Apr 01, 2013 8:31 am

A resonance bump is very useful for setting the frequency of an HPF. For a kick drum this might be all that's needed to get both an appropriate HPF and a little boost of the fundamental for weight.
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Re: What is a "resonance" peak used for, why is it so common at the cutoff frequency of filters?

Postby Hugh Robjohns » Mon Apr 01, 2013 9:28 am

BJG145 wrote:I don't get why resonance crops up in EQs either, and it's not particularly easy to turn up info on where it came from, or why or how people use it.

It's essentially a side-effect of trying to make the attenuation slope steeper -- or in other words of trying to make to making the high or low-pass filter more 'selective' in what it passes and what it stops.

In most audio mixing applications a resonant peak is unhelpful and undesirable, but there are times occasionally when a narrow-band emphasis is handy... and it is an inherent part of the accepted sound of subtractive synthesis instruments.

It is often included on plug-in filters just because they can and its makes the plug-in look more versatile, rather than because veryone uses it all the time!

H
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Re: What is a "resonance" peak used for, why is it so common at the cutoff frequency of filters?

Postby alexis » Mon Apr 01, 2013 5:45 pm

Hugh Robjohns wrote:
BJG145 wrote:I don't get why resonance crops up in EQs either, and it's not particularly easy to turn up info on where it came from, or why or how people use it.

It's essentially a side-effect of trying to make the attenuation slope steeper -- or in other words of trying to make to making the high or low-pass filter more 'selective' in what it passes and what it stops.

In most audio mixing applications a resonant peak is unhelpful and undesirable, but there are times occasionally when a narrow-band emphasis is handy... and it is an inherent part of the accepted sound of subtractive synthesis instruments.

It is often included on plug-in filters just because they can and its makes the plug-in look more versatile, rather than because veryone uses it all the time!

H

Thanks, Hugh, my gut feeling about it was apparently not far off it seems.

When I choose the HPF in Cubase with vs without the resonance peak, the actual slope doesn't visually look different between the two. How does that tie in with your statement, "It's essentially a side-effect of trying to make the attenuation slope steeper ...". ... is it all cosmetic now, i.e., just a peak pasted on to a plain old HPF, to mimic what used to be an unavoidable artifact in the analogue filter days?
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Re: What is a "resonance" peak used for, why is it so common at the cutoff frequency of filters?

Postby Hugh Robjohns » Tue Apr 02, 2013 10:14 am

alexis wrote:When I choose the HPF in Cubase with vs without the resonance peak, the actual slope doesn't visually look different between the two.

It probably is, but it can be a subtle thing to spot on screen. The fig 4 diagram in the propellerhead link that Hollowson gave earlier shows the effect very clearly.

H
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