[sdiy] RE: [AH] Parametric EQ

[John Mahoney]

At 05:58 PM 2/20/2010, Greg James wrote:
>I've suggested this before (maybe on other lists): It would be swell if
>someone designed a single-channel parametric EQ PCB that allowed full
>control over frequency, bandwidth, gain, and whatever else could be thrown
>in for good measure. Then, the DIY crowd could adapt it to whatever format
>they wanted. Did I mention CV control of the parameters? One could then
>decide how many channels they want (3, 4, 16???) to build out a super EQ of
>their own size. I know I'd be interested in doing this in MOTM format.

Oh, so you want a multiple (splitter), VCFs, VCAs, and mixers. Hmm, 
yeah, I don't see any PCBs available for those. ;-)

The multiple splits the input signal into several parallel paths. 
Each path would have a VCF and a VCA.

State-variable filters offer low pass, high pass, and band pass modes 
with voltage control over frequency and bandwidth.

Voltage-controlled amps give you control over level.

A mixer (or "summing amp" or "summer") would used to combine the 
signals of multiple VCF-->VCA chains.

By the way, Cwejman makes a VC EQ module:
<http://www.cwejman.net/vceq-3.htm>http://www.cwejman.net/vceq-3.htm

John