Just a thought.

[Smilen Dimitrov]

At 08:07 AM 11/9/98 , you wrote:
>
>>      Is it possible to have a band pass filter act as a lp or hp filter.  
>> I was thinking I could drop the input signal frequency, run it through 
>> the filter, the raise it back up the same amount.  This would be the low 
>> pass.  Has this been done, or is it too far off-base?
>> Maybe the filter would not be able to span the entire Freq range.
>> Any thoughts?  Thanks.
>> 
>> PS
>> 
>I can't see how your proposal will work.
>
>Why note use a state var filter? hp. lp. bp notch at the same time.
>
>m.c.
We had something like that in telecoms class, a theoretical circuit, it was
actually the following - multiplier with your input signal and a sin(w0*t)
function, then a bandpass with w0 central frequency, and then another
multiplier with sin(w0*t) or something like that (I don't exactly remember
the exact block diagram) and at the output I think you get something like
LP (or maybe it was LP in the middle and you get a BPP output.. hmmm...
acn't remember really). But, we used that just as a theoretical model to
analyse bandpass noise - eventually to get to Rayleigh and Rice
distribution curves. So, I guess it could be done, but, I doubt many
benefits in the audio field. 
cheers