full-range bell filter - is there one?

For a compressors side-chain I am looking for a bell-filter that goes from 30 to 16000 Hertz (or close).
Is there any schematic out there or any idea how to do this?
Since it is only in the SC the sound does not matter at all. Noise is no problem too.
But all the schematics I found were like 60 to 1000 and 1000 to 16000 Hertz. That would mean switching, which I'd like to avoid to keep this section simple.

regards

Chris

A sweepable bandpass filter that can cover the whole audio band with no range-switching? That's a tough one. You might be able to do it with a SVF and a really high-value dual pot :wink:

I've always used band-switching in cases like this (and the inverse case, such as a notch filter for a distortion analyzer) because otherwise the range of the control is too wide to allow honing in on a particular frequency with ease.

Yes,

I thought that this could be a problem. It's just I'm so much used to scan the whole freq-range in these nice little windows of all these Plug-In-EQs with mouse or encoder...
So I also thought about a switchable version, maybe even with low/high-shelve-options. But I'd really like to only have 2 pots: freq. and cut/boost.
Can you share one of your mentioned schematics, Dave?
I thought, I could do something like the Neumann W492, but I#m not shure, how to make this switchable... Any idea on this?

Chris

The tricky part is the tracking of the two pot elements, especially at the high frequency end.

State variable topologies are probably the way to go all right. You will want a Q adjustment as well as the frequency. There are probably some representative designs on the web somewhere.

thanks bcarso,

state-variable is a good idea, i think. i will try my old 'formant'-synthesizer-filter for that...

chris

the sontec midband filter goes from 140Hz to 8.2KHz in one sweep. maybe this is good enough? this is the largest sweeprange I´ve seen so far...

http://www.thediypill.phx.com.br/DIY_SONTEC/MEP250a_schemo.jpg

steff

Well, for a sidechain-filter this could really do. And if not, I could make it switchable for low and high-shelve, for the left frequency-range. I will give it a try!

thanks

Chris

ChrisS, a friend of mine did his diploma on state-variable filter design. He´s a heavy guy in that field. If you´re interested I can link you up
Jens

[quote author="bcarso"]The tricky part is the tracking of the two pot elements, especially at the high frequency end.

State variable topologies are probably the way to go all right. You will want a Q adjustment as well as the frequency. There are probably some representative designs on the web somewhere.[/quote]

With a state variable filter, and low to medium Q factors, precise tracking of the two pot elements may not be all that important.

If you look at LC-based EQs, where often one L value is shared for two or even more (switched) frequencies, you always have different Q for different center frequencies. A change of Q by factor 2 or more is not uncommon. And with a SVF, you can have an extra pot for Q adjustment, so if Q doesn't stay constant over the whole range because of pot mistracking, you can still correct it.

And another thing: In music synthesizers it's standard to have *voltage controlled* filters that sweep over the whole audio range. You just replace the dual pot with a dual OTA. A tad too noisy for genearal audio applications, though. But when you replace these cheap OTAs with a pair of THAT VCAs, that should be good enough. And you can even include it in your automation! (;->)

JH.

@ JENS: Ja, bitte lenk mich ab, ehh link me up!

@ JÜRGEN: Noise doesn't matter for sidechain, but I wouldn't go for the 'automation'-option anyway, so pots could be used. But I'd like to hear ideas for when to use that automation in a senseful way...
Do you have an idea for a simple circuit? I will take a look at Lancaster 'Active-Filter-Cookbook'.
thanks to both of you

Chris

[quote author="chriss"]Do you have an idea for a simple circuit? [/quote]

Standard State Variable filter. Dual 1meg potentiometer with 1k8 series resistor. 5.3nF capacitors (4.7nF || 680pF will do). Use an opamp that can drive the 1k8, and has high input impedance.

JH.

Oh yes, for high frequencies being on the cw side, you'd need a reverse audio taper pot.

JH.