Filter Poles - what are they?
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- KVRAF
- 10597 posts since 13 Jun, 2004 from Alberto Balsam
When a filter has X poles, what does that mean?
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- KVRAF
- 2548 posts since 7 Jul, 2003 from Huntington, WV
If it has only X poles, then the filter is a female. It would need a Y pole to be a male filter.Chase wrote:When a filter has X poles, what does that mean?
McLilith
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- KVRAF
- 4330 posts since 20 Feb, 2004
It basically refers to the dB/octave frequency dropoff rate on the "active" side of the filter (the side where frequencies are filtered off the signal). A 4-pole lpf will have a slope that's 1/2 as steep as an 8-pole lpf for frequencies above the filter cutoff value.
I believe that the "pole" terminology came about because of the specific electronics which were used to create these filters in pre-VST days.
I believe that the "pole" terminology came about because of the specific electronics which were used to create these filters in pre-VST days.
A well-behaved signature.
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- KVRAF
- 4330 posts since 20 Feb, 2004
I didn't think females had "poles" at all!McLilith wrote:If it has only X poles, then the filter is a female. It would need a Y pole to be a male filter.Chase wrote:When a filter has X poles, what does that mean?
McLilith
A well-behaved signature.
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- KVRist
- 317 posts since 20 Feb, 2005
in practical use: a higher number of poles gives a sharper cutoff.
in theoretical terms:
http://www.maxim-ic.com/appnotes.cfm/appnote_number/733
in theoretical terms:
http://www.maxim-ic.com/appnotes.cfm/appnote_number/733
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Voidoid Surrealist Voidoid Surrealist https://www.kvraudio.com/forum/memberlist.php?mode=viewprofile&u=41079
- KVRAF
- 4048 posts since 18 Sep, 2004 from Places far less tedious than this blue trainwreck...
Usualy goes somthing like this.
1 pole=6dB
More poles=steeper filtration
2-pole filter=12dB/octave
4-pole filter=24dB/octave
Either that, or it has something to do with a dead pope...
1 pole=6dB
More poles=steeper filtration
2-pole filter=12dB/octave
4-pole filter=24dB/octave
Either that, or it has something to do with a dead pope...
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- KVRist
- 263 posts since 31 Jan, 2005 from perth, australia
2 pole is my favourite, it's modest and understated, like me
4 pole is like OooH LOOK AT ME I am USInG A FiLTER , it's way too obnoxious and attention seeking for me
know what i'm saying?
4 pole is like OooH LOOK AT ME I am USInG A FiLTER , it's way too obnoxious and attention seeking for me
know what i'm saying?
blasphemy is a victimless crime
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- KVRist
- 180 posts since 19 Apr, 2004 from Espoo, Finland
In theory it means that the denominator of the transfer function polynomial has X zeroes. In practise it means that the total combined falloff rate of the filter is X*6dB/octave.Chase wrote:When a filter has X poles, what does that mean?
For lowpass filters 4 pole would mean 24dB/oct. For bandpass it would mean 12dB/oct (as you have two slopes).
2 pole filters.-
- Skunk Mod
- 21249 posts since 10 Jun, 2004 from Pony Pasture
Ah, thank goodness some still remember the Olden Dayes and the maths behind the sound. :-)antti wrote:In theory it means that the denominator of the transfer function polynomial has X zeroes.
Meffy
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- KVRer
- 29 posts since 5 Aug, 2001
No, the term pole is because of the mathematical formulation of a filter in Laplace or Fourier space.JerGoertz wrote: I believe that the "pole" terminology came about because of the specific electronics which were used to create these filters in pre-VST days.
antti decriped that aswell.
I am just doing that stuff in my studies at the moment, just more general not for audio.
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- KVRAF
- 2327 posts since 13 Apr, 2004 from Vancouver, Canada
Churchy wrote:2 pole is my favourite, it's modest and understated, like me
4 pole is like OooH LOOK AT ME I am USInG A FiLTER , it's way too obnoxious and attention seeking for me
know what i'm saying?
HAH! Thanks for that read! Best laugh I've had all morning!
Cheers.
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- KVRian
- 1243 posts since 24 Oct, 2003 from Maine
The filter takes away 6 db of volume an octave above the filter cutoff point for each "pole."
It then continues at that rate.
ex.
A 2 pole LowPass with a cutoff of 500hz.
In the next octave, the volume level of all frequencies will go from 0 dB to -12 dB. An octave after that, -12 to -24, then -24 to -36, etc etc, until you can no longer hear anything.
If it's a 4 pole, it's 24 dB per octave. 0dB to -24 in octave one, -24 to -48 in the next octave, etc.
Here's a graph showing what a lowpass filter looks like
(yes it goes way beyond the audible frequecy range, it's the best I could find)
See where it slopes downwards? The "poles" describe how steep that slope is. How immediately the volume goes from 0 dB to below audible level. It's measured in dB per octave, as described above. "Poles" just mean 6dB per octave for each pole. The more poles, the steeper the slope.
It then continues at that rate.
ex.
A 2 pole LowPass with a cutoff of 500hz.
In the next octave, the volume level of all frequencies will go from 0 dB to -12 dB. An octave after that, -12 to -24, then -24 to -36, etc etc, until you can no longer hear anything.
If it's a 4 pole, it's 24 dB per octave. 0dB to -24 in octave one, -24 to -48 in the next octave, etc.
Here's a graph showing what a lowpass filter looks like
(yes it goes way beyond the audible frequecy range, it's the best I could find
)See where it slopes downwards? The "poles" describe how steep that slope is. How immediately the volume goes from 0 dB to below audible level. It's measured in dB per octave, as described above. "Poles" just mean 6dB per octave for each pole. The more poles, the steeper the slope.
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- KVRian
- 649 posts since 30 Oct, 2004 from Brighton, UK
And resonance?
Is that the little bump before the slope down?
Is that the little bump before the slope down?