Suggestion

[Quentin Spencer]

The following is a suggestion for anyone interested in a project. I may 
eventually try to do this myself, but I thought I would mention it here 
in case someone else has an interest in it.

In MATLAB 7, the filter design function remez has been deprecated in 
favor of a function called "firpm" (the letters PM meaning 
Parks-McLellan). In addition, a new filter function has been added 
called "firls", which uses a least-squares design approach. The 
functions firpm and firls use similar calling conventions to the old 
remez function. I think it would make sense to eventually move "remez" 
to "firpm", with perhaps a remez.m script that calls firpm (this is what 
appears to happen in MATLAB 7).

I have found the firls function to be quite useful, for reasons 
described below. Writing the code for the firls function could be a bit 
of a project. I have found a pretty decent description of how it works 
at http://cnx.rice.edu/content/m10577/latest/ . It appears to me that 
unlike the Parks-McLellan algorithm, this approach is non-iterative, so 
I think it could be reasonable fast written as an m file.

While these filters do not satisfy the equiripple constraint of the 
Parks-McLellan approach, there are situations in which they can be 
desirable. One case is where the specifications make it difficult for 
the Parks-McLellan algorithm to converge. In my experience least squares 
filters tend to achieve a better average stop band attenuation for the 
same filter length than their equiripple Parks-McLellan counterparts, 
which makes them desirable in situations where exactly meeting a certain 
ripple level is not critical.

regards,
Quentin