[sdiy] multimode matrix filter question

[cheater cheater]

Both. And a switch.

D.

On Tue, Oct 19, 2010 at 19:15, David G. Dixon <dixon at interchange.ubc.ca> wrote:
> Hey Team,
>
> This is a fairly arcane question with a big boring windup, but, oh well,
> here goes:
>
> I'm designing a multimode matrix filter interface for my 2164 4P LPF, and
> I'm in a little bit of a quandary about what to do about overall gain for
> some of the derived filter modes.  For example, a +12dB/-12dB BP filter mode
> has the following general transfer function:
>
>   s^2
> ---------
> (s + 1)^4
>
> If the following convention is used to describe the gain factors for the
> cascaded 4P LPF input and four outputs:
>
> A = gain factor of the LPF input
> B = gain factor of the (inverted) 6dB LPF output
> C = gain factor of the 12dB LPF output
> D = gain factor of the (inverted) 18dB LPF output
> E = gain factor of the 24dB LPF output
>
> then this BP response can be obtained via the following gain factors:
>
> {A,B,C,D,E} = {0,0,1,2,1}
>
> However, at zero resonance, this gives -12dB attenuation at the centre
> frequency.  To obtain 0dB attenuation (i.e., unity gain) at the centre
> frequency requires the following transfer function:
>
>  4 s^2
> ---------
> (s + 1)^4
>
> which requires the following gain factors:
>
> {A,B,C,D,E} = {0,0,4,8,4}
>
> So, finally, here is my question.  Do you think it would be better to design
> all of the various filter responses so that the maximum amplitude at zero
> resonance is roughly 0dB, or rather to do whatever is dictated by the
> general transfer functions?  What would you want from such a filter?  Note
> that setting the overall gain of each response involves altering the value
> of a single (feedback) resistor, so it's not a big deal to change it after
> the fact.
>
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