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Subject: virus filter

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Original Message Date: 24-Sep-02 @ 03:37 AM - virus filter

liquidphire

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Something I noticed while playing with the Virus - when I have one of the filters' Cutoff fully open and I increase Resonance I don't hear that sharp, bright (resononant?) sound as I do on other synths (Supernova, Waldorf Q & JP-8000) using a saw wave, instead the sound volume seems to be attenuated slightly. Can someone tell me why is this happening? Does the Virus have a different filter structure then those other synths I mentioned? I like that Saw sound with a fully open filter and Resonance at 90%, does that mean I can't get it with Virus?

Thanks in advance.

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Message 21/32 26-Sep-02 @ 01:15 AM - RE: virus filter

psylichon

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Jesus, give me a break man. I just made a comment about slopes and now I have to justify my career.

me - "some hf signal will always be attenuated (unless it's somehow calibrated to compensate for the slope.. on the Nova this doesn't appear to be the case). "

I can only comment on the gear I have. On the Nova there seems to be an absolute top throw for the filter, and using a filter of gentler slope attnuates more high frequencies. If you have a Nova, check it out yer damn self. It makes sense logically, it just depends on how the filter is designed. So fuck off.

psylichon

"professional" means I get paid occasionally, it doesn't imply skill. I've been known to make mistakes, too.

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Message 22/32 26-Sep-02 @ 02:23 AM - RE: virus filter

influx

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ahahahahahhahaha. you guys are so fucking pedantic sometimes

and Im NOT!

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Message 23/32 26-Sep-02 @ 03:35 AM - RE: virus filter

liquidphire

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I've just read that Virus's filters don't self-oscillate, that's why they don't sound the way JP-8000's filter does

SCORPION, you hit the nail on the head, on the Virus, with a filter fully open Resonance starts acting like volume control. And you explained everything in a very clear manner. Thank you!

Peace!

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Message 24/32 26-Sep-02 @ 04:23 AM - RE: virus filter

psylichon

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{sigh}

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Message 25/32 26-Sep-02 @ 04:45 AM - RE: virus filter

SCORPION

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I thought I could have done better explaining. But Im happy that I can help you.

Your welcome!

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Message 26/32 26-Sep-02 @ 12:52 PM - RE: virus filter

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No i'm just confused, sure if the slope of a filter is 24bd it'll slope slower/gentler, and so there will be more lo freq' signal relative to high freq, but I just meant you refer to 'Q' but 'Q' to me is the variable of the filter slope, so i was confused about you referring to moving the 'Q' on a fixed 24bd filter - ?? - But you probably meant something different?... it might be Uk/US translation issues?

___________________________________

I had an idea for a script once. It's basically Jaws except when the guys in the boat are going after Jaws, they look around and there's an even bigger Jaws. The guys have to team up with Jaws to get Bigger Jaws.... I call it... Big Jaws!!!

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Message 27/32 26-Sep-02 @ 01:01 PM - RE: virus filter

milan

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sorry psyly. it actually doesnt make any sense, but if you feel like that i wont bring it up anymore... sigh t.

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Message 28/32 26-Sep-02 @ 02:47 PM - RE: virus filter

j-type

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> sure if the slope of a filter is 24bd it'll slope slower/gentler, and so there will be more lo freq' signal relative to high freq

a 24dB slope is steeper than a a 12dB slope, so it cuts more high frequencies for a given cutoff point than does a 12dB filter.

the bottom line is that a 12dB LPF lets more high freqs through than a 24dB LPF for a given cutoff point.

As for Q (=resonance), boosting the Q (cranking up the resonance) causes LPFs to tend towards band-pass behaviour as the freqs around the cutoff point are boosted (note how bass disappears when you crank the res). in effect, the slope of the filter becomes steeper and steeper. you change the Q of the filter when you increase the res. Q is the Quality of the filter. novations have the Q-norm feature which seems to avert the detrimental side-effects (loss of bass).

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Message 29/32 26-Sep-02 @ 06:39 PM - RE: virus filter

psylichon

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You're right, the filter cutoff is fixed at the top, and changing the slope only effects signal above the cutoff.

I ran my Nova experiement again and found I was wrong. I actually restored a totally vanilla patch from ROM and used that. There must have had some other parameter in yesterday's test patch that I was hearing. Sorry for the confusion.

psylichon

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Message 30/32 26-Sep-02 @ 07:08 PM - RE: virus filter

nomad

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one thing (ok, this will be pedantic influx, but at least it is potentially interesting :--) i hope that doesn't become a yellow circle. (i hope i get this right, a lot of it is from memory)...

anyways, Q is often interchanged with resonance, because they're about the same thing; just usually, for those 'out there' not in the music world, they're not designing filters to sound good with the resonance up, actually they're trying to design filters with the maximum cutoff and no ringing whatsoever. most practical non-musical reasons for filtering (and there are many) have totally different goals. Q=quality comes from the internal gain structure; as you increase feedback in the system, you can make the cutoff steeper, in exchange for some 'ripple' or 'ringing' at the point of cutoff.

so, in a real filter, it's not really a strict '12 db' or '24 db' response. the poles do have a large influence on the filter response, but so does Q - when Q is low, we have no ringing, but the frequency slope isn't as steep. as we bring Q up, the filter slope gets steeper, but we start 'ringing'. ringing equals that traditional boost around the cutoff. the higher Q, the steeper the cutoff still but the boost is higher. so there really is more going on than just a boost.

another interesting feature of this is that in a real analog filter, you don't just get one boost right at the cutoff. it's more like a ripple in a pond.. a large boost right at the cutoff, a smaller boost a little lower in frequency, an even smaller boost farther down, fading away (these 'ripples' as they are called also go above the cutoff frequency, but we are generally so far down at this point they are irrelevant). the smaller ripples do not affect the signal near as much as the main ripple, but they could have some effect...

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