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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 11/32 25-Sep-02 @ 11:29 AM - RE: virus filter

Steve Roughley

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If I recall correctly, in the Virus manual, it states that the Virus filter doesn't self-oscillate, meaning that it is designed differently, and this is probably the cause. I can't find where I read this but I'll have a good look and I'll get back to you.

regards.

steve.

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Message 12/32 25-Sep-02 @ 07:30 PM - RE: virus filter

influx

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"A 24 dB/octave filter would allow more of the saw wave through than a 2- or 3-pole filter. "

uh....

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Message 13/32 25-Sep-02 @ 07:36 PM - RE: virus filter

psylichon

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Yeah, I know... poorly worded.

I meant a fully opened 24 dB/oct lowpass filter fully opened would most likely pass more signal than a LP filter with a gentler slope.

In fact, I'm playing a raw saw patch on me Nova right now and switching between the 12/18/24 dB filter. I'm right! Nyah nyah! :}

psylichon

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Message 14/32 25-Sep-02 @ 08:53 PM - RE: virus filter

milan

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so how would a filter with a 24dB/octave rolloff pass higher frequencies than a filter with only 12dB/octave rolloff? i�m really curious.

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Message 15/32 25-Sep-02 @ 10:12 PM - RE: virus filter

influx

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yeah...I really dont get that one. I think youre trippin

wouldnt any filter sound the same as the next wide open?

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Message 16/32 25-Sep-02 @ 10:18 PM - RE: virus filter

psylichon

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Check it ^^^^

I didn't say it would pass higher frequencies, I said it would pass more signal.

Think about it: An fully open lowpass filter should pass all signal. The only thing is filters have slope, so 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). Hence a gentler slope, less signal.

None of this is even remotely important, I just don't have a job right now.

psylichon

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Message 17/32 25-Sep-02 @ 10:54 PM - RE: virus filter

blacktrax

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Sure, you're right psy ;-)

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Message 18/32 25-Sep-02 @ 11:00 PM - RE: virus filter

SCORPION

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Yes I dont know how the nova's filter behave but I do know how the Virus and the JP 8080 behaves.

The filters on these synths actually lose frequency or signal when your at 24 db mode. Now if you have the filter wide open with no resonance both the Jp 8080 and the Virus will see no loss in signal or freq quality no matter if its 12 or 24 db mode. On the Jp 8080 if you turn up the res with the filter wide open the waveform will start to atenuate and you will also hear the Q gain or res gain if you like. On the Virus if the filter is wide open and you turn up the q gain it will not atenuate the waveform but instead act more like a volume control. The more res you give the quiter the waveform gets.

Now if you have the filter half way open with no resonance and you switch from 12 db mode to 24 db mode you will notice that in 24 db mode on both the Virus and the Jp 8080 the waveform sounds alittle quiter and as well less quality meaning the 24 db mode is not letting all the signal out of the waveform. The waveform in 24 db mode sounds darker in tone in 12 db mode the waveform will sound brighter.

Now add some resonance and you will here the attenuation as well the Q gain. Both synth will sound more and more raspier as you add more Q. The difference is on 24 db mode the JP 8080 goes to self oscillation becuase the Q gain is greater than the cutoff slope. So when you move the cut off with full gain on the JP at 24 db mode it will sound like a whistle. This is the full feedback of the Q. I can say even though the JP 8080 can self oscillate it is still not perfect oscillation becuase you can still hear very little of the waveform. Its just in the background very quitely. But its close enough to be considered self osc.

The Virus with full q wont self osc becuase its filter cutoff is greater then the Q factor. Yes you can create a self osc like sound on the Virus if you programe it right but all it is is shapeing the waveform with the cut off slope to fit that self osc quality of sound. which is totaly different then that of what the JP 8080 does.

I admit im no signal expert but I can tell you what my ears are hearing. And this is how those filters sound to me.

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Message 19/32 25-Sep-02 @ 11:08 PM - RE: virus filter

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eh?... but 'Q' is the filter slope shurely?.... how can you have a Q and a fixed 24db filter?

___________________________________

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 20/32 25-Sep-02 @ 11:58 PM - RE: virus filter

milan

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umm psylichon... take a look at this, and tell me why dont i have your job, mr. professional engineer? eh?

m ;)

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