Lee:
Since we are trying to stay at the 3rd grade level, I will spare you
the mathematical definition of the difference.
The observable difference is that if you apply a single pulse to the
input of a Finite Impulse Response (FIR) filter, the output of the
filter will be a finitely long train of non-zero pulses, but if you
apply a single pulse to the input of an Infinite Impulse Response
(IIR) filter, the output of the filter will be a train of non-zero
pulses that never ends. After a settling time, the value of the
remaining pulses will become very small, but they will never quite go
to zero. The IIR response is akin to the "time constant" response of
a linear analog circuit.
(I could get into details like recursive versus non-recursive, but
that is past 3rd grade level.)
Advantage of the IIR filter: It is computationally cheaper than a FIR
filter. In other words, if I want to obtain a specified filter
response, an IIR filter will process the signal in fewer clock ticks
than a FIR filter.
Disadvantage of the IIR filter: It is susceptible to computational
instability. In other words, unless you are extremely careful about
both the design of the filter and the type of signal you apply to it,
the filter output will gyrate wildly between the largest and smallest
number that the machine precision allows; this is the machine's way
of approximating a response that "approaches infinity."
Advantage of FIR filter: It is inherently stable. A bounded input
must produce a bounded output. In most engineering applications the
inherent stability is worth the cost of the extra clock ticks
required for the FIR filter.
73,
Steve Kercel
AA4AK
At 10:26 AM 7/24/2008, Lee Buller wrote:
I've been doing some reading on the new firmware. I would like
someone to explain (like I am a 3rd Grader) the different between
IIR Filtering and FIR Filtering. Thanks.
Lee - K0WA
"Liberal Arts Major - Mathematically Challenged - Science Wannabe -
Fascinated by Technology"
In our day and age it seems that Common Sense is in short
supply. If you don't have any Common Sense - get some Common Sense
and use it. If you can't find any Common Sense, ask for help from
somebody who has some Common Sense. Is Common Sense divine?
_______________________________________________
Elecraft mailing list
Post to: Elecraft@mailman.qth.net
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com
_______________________________________________
Elecraft mailing list
Post to: Elecraft@mailman.qth.net
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com
