Hi.

It depends a lot upon how sophisticated the filter is that you buy.  Most 
of these filters will allow you to be able to taylor the bandpass in some 
way, and most allow you to select between several different noise reduction 
algorithms.  They also usually include an automatic notch filter that can 
be enabled or disabled as the need arises.  The cheaper DSP filters (the 
audio frequency ones) such as the DSP40 from Radio Shack (made in the mid 
1990's) work about as well as the active audio filters of yesterday, but 
the better audio DSP units and most of the IF level DSPs will outperform 
all but the best active audio filters.  By the way, I still miss my Autek 
Research QF1A.  If I ever get the chance, I'll scarf up another one!

Anyway, most good DSP filters "ring" a lot less than the active audio 
filters were prone to do, and the roll off is much quicker.  For the most 
part, it is the noise reduction effects that I am not crazy about, rather 
than the bandpass, although I still like some of the better analog filters, 
especially the ones that are in my Drake R8A communications receiver.  For 
those of you who've never heard one, there is a nice receiver.  Too bad 
they never made a speech board for it.

I have one of the W9GR audio DSP units on my old Kenwood TS690S, and of 
course the Kenwood TS2000S has a IF level DSP filter.  I like to have the 
noise reduction during the thunderstorm season, but I'm not so keen about 
it this time of year.

Hopefully, that gives you a little better idea about DSP filters.

73, de Lou K2LKK



At 06:19 PM 2/6/2006 -0800, you wrote:
>Hi
>I have never used a DSP unit.  Do you get to pick which sounds it blocks or
>does it make up its own mind?
>                     God bless,
>                     Mark WZ0K
>God loves you!
>My personal prayer book.
>Add your prayer or pray for others at the following link.
>http://prayerbook.homewithgod.com/cgi-bin/prayerbook/multi.pl?131961113534708:24:0
>
>http://lists.topica.com/lists/funhamradio.
>
>http://funhamradio.bloki.com
>----- Original Message -----
>From: "Louis Kim Kline" <[log in to unmask]>
>To: <[log in to unmask]>
>Sent: Monday, February 06, 2006 4:12 PM
>Subject: Re: filter question
>
>
> > Hi.
> >
> > A DSP filter can do this to a degree, but it generally introduces
> > distortion into the intended signal, because in order to remove the random
> > noise frequencies, it is inevitably also removing a little of the intended
> > signal, giving it a kind of watery sound.  I have used DSP filters for
> > about ten years, and there are times when they are handy, but they are
> > definitely not the be all and end all, and there are times when I actually
> > prefer a good crystal filter to a IF level DSP filter.  Just goes to show
> > that there is no one perfect solution to those unwanted signals and noise
> > sources.
> >
> > 73, de Lou K2LKK
> >
> >
> >
> > At 10:16 PM 2/5/2006 -0800, you wrote:
> >>Hi
> >>A few years ago I had an idea for a filter that would remove the back
> >>ground
> >>noise on HF.  I was wondering if a digital signal processor does this or
> >>if
> >>some one had made a commercial filter to do this.
> >>     It would be a help to catch those stations that fall below the noise
> >>level!
> >>                     God bless,
> >>                     Mark WZ0K
> >>God loves you!
> >>My personal prayer book.
> >>Add your prayer or pray for others at the following link.
> >>http://prayerbook.homewithgod.com/cgi-bin/prayerbook/multi.pl?1319611135 
> 34708:24:0
> >>
> >>http://lists.topica.com/lists/funhamradio.
> >>
> >>http://funhamradio.bloki.com
> >
> > Louis Kim Kline
> > A.R.S. K2LKK
> > Home e-mail:  [log in to unmask]
> > Work e-mail:  [log in to unmask]
> > Work Telephone:  (585) 697-5753
> >

Louis Kim Kline
A.R.S. K2LKK
Home e-mail:  [log in to unmask]
Work e-mail:  [log in to unmask]
Work Telephone:  (585) 697-5753