[LAU] Mackie Onyx like channel strips?

[David Kastrup]

Ralf Mardorf <ralf.mardorf-ZCLZIpdjs0kJGwgDXS7ZQA at public.gmane.org>
writes:

> On Sun, 19 Nov 2017 13:10:24 +0100, David Kastrup wrote:
>
>> Correct.  The problem is _exactly_ that it can do whatever any other
>> can and that you have far too many free parameters to get under
>> control.  A few distinctly different good choices in practice lead to
>> better results, particularly given time constraints, than a full
>> continuum of every available choice.
>>
>> The continuum is what tool builders can work best with.  But the
>> actual use cases want ready-made tools.
>
> You could use presets for some parameters of the EQ and only change
> the desired parameters of the EQ.

Well, the art is actually distilling useful parameters.  For a grade 2
IIR I get something like parameters a1, a0, b1, b0, but manipulating
those would be a lesson in frustration.  For the LaPlace transform of
the transfer function of the high EQ (don't ask me which Onyx I was
looking at, probably the 1620 because I have it) I get something like

Pot ranges from b = -1 .. 1

Out = In*((3.47kOhm+1/(0.0033uF s)+10kOhm-b*10kOhm)|510kOhm)
        /((3.47kOhm+1/(0.0033uF s)+10kOhm+b*10kOhm)|510kOhm)

Where x|y is (xy)/(x+y) and s is the transform domain variable (for a
Fourier transform, it would correspond to 2 pi j f with j being sqrt(-1)
and f being the frequency).

Obviously, with b = 0 output and input correspond.

If we convert this to a general IIR form, we'll likely get more
polynomial coefficients than we are comfortable choosing all on our own.

-- 
David Kastrup