EQs - why cant you change the Q with slope at 6 dB?

[Caine123]

woah, after all these years i found something i never knew and i wonder why. first i though Volcano 3 is kinda bad but in SHADE it is the same:



why cant you change the resonance with slobe 6dB but with slope 12db?



why did i came across this cause about ETCH there the filter looks like this

[whyterabbyt]

>why cant you change the resonance with slobe 6dB but with slope 12db?

because 6dB filters dont resonate.

[Caine123]

>why cant you change the resonance with slobe 6dB but with slope 12db?

because 6dB filters dont resonate.

thx a lot, i need to check the values in ETCH, but why can ETCH be such a interesting slope?

[diroxe7660]

> because 6dB filters dont resonate.

Is that true for all filter designs?

[dubguy99]

> because 6dB filters dont resonate.

Is that true for all filter designs?

No, e.g. Ghz Tiltshift has 6db filters with variable resonance. But it seems to be a rare implementation.

[MirkoVanHauten]

I was told as well 6dB filters don't resonate and that there's a "workaround" of additionally processing a peak filter at the cutoff to artificially create a resonant peak.

[jackoo]

> because 6dB filters dont resonate.

Is that true for all filter designs?

In short: yes.

Long answer:

In order for a system to resonate you need two elements that can store energy, and this energy oscillates between the two storage elements. In electronic design these can be either 2 capacitors (both store electric energy), or a capacitor and an inductor (cap. stores electric energy and the coil stores magnetic energy). This has to translate into a "2 pole system".
The rate / speed at which the two elements exchange the energy is giving the so called Resonance Frequency.

Resonance can only happen when this oscillation of energy between two storing elements happens with minimum losses. The losses are defined by the Q (the quality factor). If Q is high, there are low losses and you get a very high resonant peak. If Q is low you have major losses and the resonance goes away (at Q = sqrt(2)=0.707 you lose the resonance effect completely, e.g. there is no peaking present in the transfer function anymore). The resonance knob actually models the value of the Q (quality factor).



Each energy storage element adds a so called "pole" in the Laplace form of the transfer function from input to output.
Any filter design with one pole has a 6dB / octave roll off after its cutoff frequency (actually 20[log(2)] dB).
https://www.edaboard.com/threads/why-po ... lot.38308/

In order to get resonance, you need systems having transfer functions with at least two conjugate complex poles. These conjugate poles always come in pairs (real+ i*imaginary, real - i*imaginary). So you need at least two poles to get a resonant transfer function.

The two poles contribute each with 6dB / octave, so if you want resonant filters, you have at least 12 dB/octave roll-off.

[MrBeagleton]

so if you want resonant filters, you have at least 12 dB/octave roll-off.

Well, technically at least 2-poles. What do you think about the method mentioned above of using a 2-pole peaking filter in series with the 1-pole? That gives you a 3-pole filter which maintains the 6 dB/oct roll-off, but with resonance.

Not saying this is the proper solution (there isn't one), but it works reasonably well.

[DubLifeSD]

Acon Equalize2. Variable resonance at 6db and 3db.

[MrBeagleton]

Acon Equalize uses FIR filters. Totally different animal from Shade and not something you can modulate quickly.

[MrBeagleton]

why cant you change the resonance with slobe 6dB but with slope 12db?

why did i came across this cause about ETCH there the filter looks like this

It says 2 pole, though. That's 12 dB/oct, not 6.

[gentleclockdivider]

>why cant you change the resonance with slobe 6dB but with slope 12db?

because 6dB filters dont resonate.

Cough ..
Korg ms20 hp filter
Cough…
Resonance = feedback , even when it’s just one pole filter like
the ms20 hp

[jackoo]

Of course you can get any shape (transfer function), incl. resonance using multiple filters that act on the same frequency range (or a filter bank, which is what an EQ actually is). But then the whole system has more than 1 pole.

Positive feedback can inject energy into the system in order to sustain oscillations. This feedback may move the system's poles on the imaginary axis (turning real poles into complex conjugate ones that can resonate). But again, not a 1 pole system.

[imrae]

>why cant you change the resonance with slobe 6dB but with slope 12db?

because 6dB filters dont resonate.

Cough ..
Korg ms20 hp filter
Cough…
Resonance = feedback , even when it’s just one pole filter like
the ms20 hp

If I understand the schematic correctly, the MS-20 high-pass is a 2-pole feedback loop but the input and output are one pole apart. It wouldn't resonate if you removed the other pole?

[whyterabbyt]

>why cant you change the resonance with slobe 6dB but with slope 12db?

because 6dB filters dont resonate.

Cough ..
Korg ms20 hp filter
Cough…
Resonance = feedback , even when it’s just one pole filter like
the ms20 hp

cough....

6db taps from a higher-order filter can resonate, albeit the resonance is that for the slope of the higher-order filter, not as it 'should' be.
6db filters dont resonate.

viewtopic.php?p=5641786#p5641786

And read Stinchcombe's paper if you actually want to know what's happening with the topology of the MS20 highpass. Clue : there's a 12dB filter being used in there.