[sdiy] Passive filters and impedances

Donald Tillman don at till.com
Sun Nov 1 20:15:46 CET 2015


> On Nov 1, 2015, at 10:23 AM, Richie Burnett <rburnett at richieburnett.co.uk> wrote:
> 
>> That's how the Roland Diode Ladder filter works.
> 
> True, but it also has much additional circuitry that puts negative feedback around the sloppy un-buffered ladder to tighten up its response into something more musically usable.

Not that much circuitry.  And an analysis of the Roland Diode Ladder filter requires the ability to do an analysis of the original RC ladder, Tom's original request.

I'm harping on this because electronic music has always had respect for both the abstract and the practical.  In the abstract an RC ladder does a crappy job of filtering, but in practice it finds many interesting musical uses.

> Ok, perhaps unbuffered filters *are* useful in applications like guitar amps if you don't mind complex interactions between the various tone controls. Fender tone stack for example!

Exactly.

The goals of hi-fi tone controls are: flat response at 12 o'clock, subtle adjustments at the ends of the spectrum, and no interaction between the controls.

It's the exact opposite in the guitar amplifier world; we don't care about flat response at 12 o'clock (and in fact the instrument sounds kind'a dull with a flat response), wild variations in timbre are a feature, and interaction makes it more interesting.

It's the difference between producing music and reproducing music.

  -- Don

--
Don Tillman
Palo Alto, California
don at till.com
http://www.till.com




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