[sdiy] RE: [AH] Parametric EQ

[Tom Wiltshire]

On 21 Feb 2010, at 22:24, Neil Johnson wrote:

> Hi Tim,
>
>> What I'm wondering is, could a 'standard' expo converter be
>> used for the same purpose? Instead of using another 2164 section
>> (which, if you're already using all four sections of the chip,
>> requires you to use a second 2164), could you just use a couple of
>> transistors and an op-amp?
>
> In principle yes it would work - no reason for it not to.  BUT ...  
> you lose the inherent thermal and behavioral connection between the  
> gain cell and the expo converter if you use an external converter.   
> Of course, in some applications (e.g., filter resonance, filter  
> frequency sometimes) this may not be so important.


I agree with Neil that it's better to do the linearization on the  
same SSM2164, so I think I like David's idea of separating the mixer  
VCAs out onto their own chip. That way you use 4 sections of a  
SSM2164 for each filter (2 filter stages, 2 for linear resonance VCA)  
and then have a separate SSM2164 to mix 4 bands together. Of course,  
it's only convenient if you add bands in groups of four, but you  
can't have it all ways.
Anyway, if there was a DAC controlling it, I'd still save the  
hardware and use a lookup table to linearize the resonance response.  
But that's just me.

T.