From: "Bill Sloman"
Subject: Re: What filer has equal ripple phase response, and where can I find the pole positions for a 4th order filter?
Date: Sun, 19 Jan 2003 00:16:17 +0100
Organization: Planet Internet
NNTP-Posting-Date: 18 Jan 2003 23:17:00 GMT
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
"Tony Roe" wrote in message
> I want to make a simple adjustable analog time delay to time-align
> that use Linkwitz-Riley crossovers.
> Whereas Butterworth filters have maximally-flat amplitude response,
> filters are a more general case, with equi-ripple amplitude response.
> Bessel filters have maximally-flat phase response, but what filter is a
> general case, with equi-ripple phase response.
> I'm asking because I would need to use an all pass network based on 6th
> Bessel poles (plus the 6 matching zeros of course) whereas I would hope I
> get by with 4th order if I relax the spec to equi-ripple phase (say +/-3
Electronic Filter Design Handbook/Book and Disk by Arthur B. Williams,
Fred Taylor (Contributor)
Hardcover 3rd Bk&dsk edition (October 1995) McGraw Hill Text; ISBN:
0070704414 ; Dimensions (in inches): 2.18 x 9.27 x 6.29
Amazon.com Sales Rank: 80,711
Amazon says that it is out of print, but a good universiyt library will have
it, and there were enough sold that Amazon should be able to get you a used
copy without too much delay.
I've only got the second edition, but that includes two equi-phase-ripple
variants of the Bessel filter - at 0.1 degrees of ripple and 1 degree , IIRR
(my copy is at work) - but there was some discussion of the synthesis
Hope this helps.
Bill Sloman, Nijmegen