[sdiy] Re: Ladder filter variations

[Magnus Danielson]

From: Don Tillman <don at till.com>
Subject: Ladder filter variations
Date: 05 Mar 2005 23:53:57 -0800
Message-ID: <m27jkljjl6.fsf at till.com>

Don,

> [Itook the liberty of changing the subject line.]
> 
> Magnus, Hairy Harry, Osamu-san, gentlefolks,
> 
> If you're interested in variations on the ladder filter, I'll suggest
> you go to the patent pdf tool:
> 
>    http://www.pat2pdf.org

How long I have wated for something similar. I've been considering hacking a
wrapper to the Espacenet server(s) to give me full PDFs. The above only seems
to track US patents, which is a significant drawback at times.

Espacenet is at:
http://ep.espacenet.com

For those wishing a different language, there exists a number of different
menu variants, so French, German or Spanish should not be a problem if you
favour them over English.

> And take a look at this guy:
> 
>   US 6,084,470
>   Filter Circuit Capable of Setting Various Filter Characteristics 
>   Shiramatsu, Nakamura, Goto
>   Kabushiki Kaisha Toshiba
>   July 4, 2000
> 
> This patent is an insane collection of unusual ladder filters.  

Many thanks for the link and the patent number. Yes, it is insanely many.
The variation together with a number of others should be a good reading,
especially if one combinds them and builds oneself a library of buildingblocks
which they effectively have done in the above patent. It however looks at a
different frequency range, plots put the cut-off in the 1-10MHz frequency range
most of the time. But then, they show the principle and with a little
different choices of components it will apply to audio.

> Also check out these:
> 
>   US 5,912,587
>   Active Filter Stack
>   Mihailovits, Beatson
>   Mitel Semiconductor
>   June 15, 1999

Interesting reading indeed!

>   US 5,225,790
>   Tunable Widband Active Filter
>   Noguchi, Rinaldis, Esling
>   Digital Equipment Corp.
>   July 6, 1993

Concentrates on one and two pole filter solutions. Notably with dual feedback
as in state-variable. Different sizes of capacitors.

>   US 3,983,512
>   Current Controlled Electrical Circuits
>   Lipscombe
>   Feedback Instruments Limited
>   September 28, 1976

Concentrates on two-pole solutions with oscillators as primary target.

> I'm sure some of these have significant musical potential.

Will do! They should be a good rub-in. Hmm... why do I feel like I need one?

> Enjoy!

Will do!

Cheers,
Magnus