[Premium-Rx] Re: Filter phase response

[Alberto di Bene]

John Reed wrote:

>I'm way ahead of you on that one.  I've done a lot of experimenting with
>audio filters: DSP, analog active and passive LC.  The best I've found for
>lowfer CW signals is a sixth order Gaussian passband shape passive LC filter
>with 30 Hz bandwidth.  Forget about the DSP filters for this application.
>They are third on the list, following active switched capacitor filters.  LC
>passive filters are the best.
>

Well, not necessarily true. Using DSP you can program either FIR or IIR 
type of filters. FIR offer
almost brick-wall shapes (depending on how much computing power you 
throw at them), nothing
like a Gaussian response. But if you program correctly an IIR filter, 
you can have your 30 Hz,
Gaussian response filter that will sound exactly like the equivalent 
analog counterpart.

But generally DSP programmers are attracted by the phenomenal skirts of 
the FIR filters,
unattainable in the analog domain, together with the myth of linear 
phase, good for processing
pulse signals, but not so needed for voice (the human ears are 
insensitive to phase) , and
those FIR filters are the one that get implemented...

73  Alberto  I2PHD