Fast Modulation of Filter Parameters
- KVRian
- Topic Starter
- 1278 posts since 31 Dec, 2008
Let me ask a question here. Why can’t a click or pop be part of correct filter behavior?
In other words, if you change a filter parameter (say cutoff) almost instantaneously to a far value, then shouldn’t the filter naturally click or pop at that moment? I would think that at least some filter designs would.
In other words, if you change a filter parameter (say cutoff) almost instantaneously to a far value, then shouldn’t the filter naturally click or pop at that moment? I would think that at least some filter designs would.
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- KVRAF
- 8114 posts since 12 Feb, 2006 from Helsinki, Finland
Well, this goes into to the question of how do we define a "click or pop" as basically any "well behaved" filter will still have a discontinuity in the first derivative when you apply instantaneous modulation. That's a 12dB/oct pop. Perhaps in some structures it might be even steeper decay, but that's what you usually expect. If you have a discontinuity in the waveform itself, that's a 6dB/oct pop/click. If you have a transient of some sort that results in an amplitude spike, then at "low frequencies" (depending on the shape of the spike) you can have a flat 0dB/oct click (in addition to potential other problems).S0lo wrote: ↑Sat May 18, 2024 10:00 am Let me ask a question here. Why can’t a click or pop be part of correct filter behavior?
In other words, if you change a filter parameter (say cutoff) almost instantaneously to a far value, then shouldn’t the filter naturally click or pop at that moment? I would think that at least some filter designs would.
- KVRian
- Topic Starter
- 1278 posts since 31 Dec, 2008
Thanks for answering mystran. But (I should have said) that I was kinda aiming that question to soundmodel as a way for him to not get locked into thinking that all pops and clicks are inherently wrong. Just because too many papers out there talk about it as being so.
I just ran a sin wave into a TPT based low pass while modulating the cutoff with a square wave LFO (slow). The output has obvious clicks at the cutoff changes. I’m not surprised at all, that’s how it should sound like. I would expect the analog counterpart to do the same.
If someone wants to eliminate that, without filtering the modulator and without modifying the filter, then I wouldn’t know what to do.
I just ran a sin wave into a TPT based low pass while modulating the cutoff with a square wave LFO (slow). The output has obvious clicks at the cutoff changes. I’m not surprised at all, that’s how it should sound like. I would expect the analog counterpart to do the same.
If someone wants to eliminate that, without filtering the modulator and without modifying the filter, then I wouldn’t know what to do.
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- KVRAF
- 8114 posts since 12 Feb, 2006 from Helsinki, Finland
Some designs might have a lowpass filter (eg. typically a single cap to the ground) on the cutoff input side to limit the modulation bandwidth. You see this perhaps more often with hybrid designs where the filter is analog but the modulation comes from a digital source, like when envelopes/LFOs are implemented with a microcontroller that is then output with a simple DAC producing a stepped waveform, but you could do it in a pure analog too (reduce high freq noise, perhaps improve servo stability, etc)... although obviously if you want to have filter FM then you have to have enough modulation bandwidth to let the FM modulation signal through.
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- KVRian
- 1167 posts since 28 May, 2010 from Finland
It can, but it's not desirable in a musical context. Ideally, we'd obviously want a filter that acts continuously across the parameters. Or that has a "cross-over" behavior built-in.S0lo wrote: ↑Sat May 18, 2024 10:00 am Let me ask a question here. Why can’t a click or pop be part of correct filter behavior?
In other words, if you change a filter parameter (say cutoff) almost instantaneously to a far value, then shouldn’t the filter naturally click or pop at that moment? I would think that at least some filter designs would.
However, if you're talking about the mere perception of two separate transients very closely to each other, then obviously it is audible as a click, but it's a corner case, because no-one really uses filters that way.
However, the original reason for the artifacts seems to be that people deal with transfer functions, even though it's guaranteed that transfer functions do not have any certain kind of continuity between them, since they're LTI.
And yes, it doesn't sound mathematically odd at all that there's a function that's parametrizable so that the the cut-off moves the filter linearly in frequency. Like the Moog ladder:
https://soundspear.com/blog/5-different ... io-filters
http://www.blaukraut.info/temp/moog_transfer.png
- KVRian
- Topic Starter
- 1278 posts since 31 Dec, 2008
Sorry, but thats just not true. What happened to all these musicians using square LFOs, stair steps, sample and hold.. etc. hundreds of use cases, you definitely don't want to smooth that. And even if you do, then just lowpass (slew limit) the modulator. Otherwise, if you forcefully modify the filter to give you a smoother response, then it's not the same filter you designed or emulated any more. It's a different filter now. If thats OK with you by design, then it's OK. But I'm sure that this can very much be undesirable in some musical contexts as it is desirable in others.soundmodel wrote: ↑Sat Jun 01, 2024 2:12 pmIt can, but it's not desirable in a musical context. Ideally, we'd obviously want a filter that acts continuously across the parameters. Or that has a "cross-over" behavior built-in.S0lo wrote: ↑Sat May 18, 2024 10:00 am Let me ask a question here. Why can’t a click or pop be part of correct filter behavior?
In other words, if you change a filter parameter (say cutoff) almost instantaneously to a far value, then shouldn’t the filter naturally click or pop at that moment? I would think that at least some filter designs would.
However, if you're talking about the mere perception of two separate transients very closely to each other, then obviously it is audible as a click, but it's a corner case, because no-one really uses filters that way.
www.solostuff.net
Advice is heavy. So don’t send it like a mountain.
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- KVRian
- 1167 posts since 28 May, 2010 from Finland
You mean that a square LFO, stair steps, sample and hold etc. are not smoothed or the process (e.g. a filter) is not smoothed?
I don't know, but doing e.g. a <= 5 ms cross-fade rarely affects the perception of continuity.
I don't know, but doing e.g. a <= 5 ms cross-fade rarely affects the perception of continuity.
- KVRian
- Topic Starter
- 1278 posts since 31 Dec, 2008
What I meant is, relative discontinuity in the modulator, and therefore potentially in the filter output can have musical value in many contexts.soundmodel wrote: ↑Fri Jun 21, 2024 12:42 pm You mean that a square LFO, stair steps, sample and hold etc. are not smoothed or the process (e.g. a filter) is not smoothed?
I don't know, but doing e.g. a <= 5 ms cross-fade rarely affects the perception of continuity.
www.solostuff.net
Advice is heavy. So don’t send it like a mountain.
Advice is heavy. So don’t send it like a mountain.