🚀 go-pugleaf

In article <1990Jul10.122121.28209@funet.fi> rk76073@naakka.tut.fi (Risto Kotalampi) writes:
>In article <3504@radio.oakhill.UUCP> you write:
>>
>>I would like to use an IIR filter in a particular application.  I 
...
>>the phase ripple can be as high as +-10 degrees and still be considered
>>acceptable correction. Any help would be apprieciated.
...
>> -Charlie Thompson
>
>A solution to your problem could be Allpass Filters. With Allpass' you
...
># Risto Kotalampi rk76073@tut.fi   # Phones :                           #

If you have the luxury of redesigning your IIR filter, I have had very good
results designing filters using Yule-Walker type techniques, certainly producing
+- 10 degrees in the passband, even for fairly funny filters (ie. low pass things
with integral 50Hz notches, notch just outside the pasband).
Reference:
Roberts and Mullis, Digital Signal Processing, Addison-Wesley, 1987

Although I used the functions delivered with Pro-Matlab from The Math Works to
do the design.

Also interesting (and of no personal design experience) is an article:
Clements, "On Causal Linear Phase IIR Digital Filters",
	IEEE Trans. ASSP, Vol 37, No. 4, Apr 1989

Good stuff -

James Taylor