[sdiy] Re:

[John L Marshall]

Bobby,

Don't take the topic off list. The filter design is very much on topic and
there are a lot of interested "listeners".

Happy New Year,
John


----- Original Message -----
From: "Robert Pietrusko" <bobby at csounds.com>
To: <cfmd at bredband.net>
Cc: <synth-diy at dropmix.xs4all.nl>
Sent: Tuesday, December 30, 2003 7:25 AM


| Hi Magnus,
|
| The best reference I have found, and the one I am
| using, is the old Van Valkenburg text "Analog Filter
| Design," which has been a bible for any other filters
| I've designed.  In this case I am using mainly
| chapters 12 and 13.
|
| The Gioffi equations in chapter 12 are used to compute
| resistor and capacitor values for a Boctor active
| filter circuit from a 2nd order transfer function.
| The result is a high-pass notch. I'm fairly certain I
| can't get this response out of a Sallen-Key design.
|
| I guess another more practical question is,  if most
| people are not familiar with this approach and I am
| having a hard time finding material, am I barking up
| the wrong tree?
|
| What is a more "standard" method of realizing
| Cauer/Elliptic filters using opamps? or even, a more
| standard method of realizing high-pass notch functions
| that are peaky at the cutoff frequency?
|
| as is  always the case for me, it's not the filter
| design, but its analog implementation that is causing
| the trouble. :) ugh!
|
| I'd be happy to message in more detail off list to
| spare the inboxes of other list members.
|
|
| -bobby.
|
|
|
|
|
|
| From: Robert Pietrusko <bobby at csounds.com>
| Subject: [sdiy] new to the list... already have a
| question :)
| Date: Mon, 29 Dec 2003 19:10:33 -0800 (PST)
| Message-ID:
| <20031230031033.93100.qmail at web41305.mail.yahoo.com>
|
| > Hi List,
|
| Hi Bobby,
|
| > I'm curious if anyone on the list has experience
| > designing Boctor High Pass Notch circuits using the
| > Gioffi equations.
| >
| > I'm working on a 10th order Cauer filter design
| (split
| > into second-order-sections which will be designed as
| > cascaded high-pass notches) and for all but the
| first
| > section I am getting negative values for my Rs and
| Cs!
| > There is an inequality involving Q, Wz and Wo that
| my
| > coefficients are violating, so I'm sure this has
| > something to do with it.
| >
| > Does anyone know of a workaround? I really need this
| > high-pass notch response for my filter (i think) and
| > I've been wrestling with it all day.
| >
| > Thanks in advance for any help you can offer.
|
| Well, excuse me for my ignorance, but do you happend
| to have a reference (or
| several) to the Boctor/Gioffi material, which I
| haven't heard about.
|
| Might I assume you are doing something in Csound or is
| this a discrete design?
| Additional details like that might help you know.
|
| Cheers,
| Magnus
|
|
|