Complex filters

Hi all,

What is the significance of complex FIR filters used? In general the inputs
are the sequences of real values, then where can the complex filters be
used?

If they are used for real inputs, then how do we interpret the complex
outputs?

Regards,
Ishtiaq.

"I. R. Khan" wrote:
> 
> Hi all,
> 
> What is the significance of complex FIR filters used? In general the inputs
> are the sequences of real values, then where can the complex filters be
> used?
> 
> If they are used for real inputs, then how do we interpret the complex
> outputs?

The most obvious one I can think of is an FIR filter which implements
the Hilbert transformer which by definition has a complex valued
output.

Erik
-- 
+-----------------------------------------------------------+
  Erik de Castro Lopo  nospam@mega-nerd.com (Yes it's valid)
+-----------------------------------------------------------+
"I think there is a world market for maybe five computers."
 -- Thomas Watson, Chairman of IBM, 1943

"I. R. Khan" wrote:

> Hi all,
>
> What is the significance of complex FIR filters used? In general the inputs
> are the sequences of real values, then where can the complex filters be
> used?
>
> If they are used for real inputs, then how do we interpret the complex
> outputs?

Complex filters usually needed
when down conversion is used,
for example, in the software radio.
Then the real signal is multiplied to the complex sine wave
and then filtered by sharp complex low pass filter.
And here at the output the positive and negative frequencies occur.

A.Ser.

"I. R. Khan" <ir_khan@hotmail.com> wrote in message
news:c1ceoq$1gtpmo$1@ID-198607.news.uni-berlin.de...
> Hi all,
>
> What is the significance of complex FIR filters used? In general the
inputs
> are the sequences of real values, then where can the complex filters be
> used?
>
> If they are used for real inputs, then how do we interpret the complex
> outputs?
>
> Regards,
> Ishtiaq.

Use Google groups search to look up a thread on this topic - we had a fairly
long discussion less than a month back.

Cheers
Bhaskar