comp.lang.idl-pvwave archive: archive » Re: How to perform the 1-D signal filter?

Home » Public Forums » archive » Re: How to perform the 1-D signal filter?

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: How to perform the 1-D signal filter? [message #58436 is a reply to message #58434]

Fri, 01 February 2008 06:16

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Wox writes:

> Example below filters in time or frequency domain:
>
>
> ; Time domain
> freq1=2.
> freq2=3.
> freq3=4.
> dtime=0.1
> ntime=1000
>
> time=dtime*findgen(ntime)
> signal=sin(2*!pi*freq1*time)+sin(2*!pi*freq2*time)+sin(2*!pi *freq3*time)
>
> ; Time domain Filter
> f_low = 0
> f_high = 2.5
> timefilter = DIGITAL_FILTER(f_low*2*dtime, f_high*2*dtime, 50.,40)
> signal=convol(signal,timefilter)
>
> ; Frequency domain
> nfreq=ntime/2+1
>
> freq=findgen(nfreq)/(dtime*ntime)
> fsignal=fft(signal)
>
> ; Frequency domain filter (instead of time domain filter)
> if n_elements(timefilter) eq 0 then begin
> steep=20.
> freqfilter= 1./(1.+(freq/f_high)^steep)
> fsignal*=freqfilter
> endif
>
> plot,freq,abs(fsignal[0:nfreq-1])^2,xtitle='frequency',ytitl e='spectrum'

Wonderful example, but I'm trying to understand this whole
subject. Do you think you could flush this out with a little
explanation of what you are doing and why you choose the terms
you use, etc.? What kind of frequency filter are you constructing
here? I don't necessarily see it doing any filtering of the signal,
at least if I pass it the original signal, rather than the signal
that had already been filtered in the time domain, as written
in your example.

Cheers,

Confused
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")

Report message to a moderator

[Message index]

		Re: How to perform the 1-D signal filter? By: Kenneth P. Bowman on Fri, 01 February 2008 06:58
		Re: How to perform the 1-D signal filter? By: Wox on Fri, 01 February 2008 09:16
		Re: How to perform the 1-D signal filter? By: duxiyu@gmail.com on Sat, 02 February 2008 07:14
		Re: How to perform the 1-D signal filter? By: Wox on Fri, 01 February 2008 08:57
		Re: How to perform the 1-D signal filter? By: duxiyu@gmail.com on Fri, 01 February 2008 06:54
		Re: How to perform the 1-D signal filter? By: David Fanning on Fri, 01 February 2008 06:16
		Re: How to perform the 1-D signal filter? By: Wox on Fri, 01 February 2008 05:27
		Re: How to perform the 1-D signal filter? By: duxiyu@gmail.com on Sat, 02 February 2008 07:20
		Re: How to perform the 1-D signal filter? By: David Fanning on Fri, 01 February 2008 17:07
		Re: How to perform the 1-D signal filter? By: David Fanning on Fri, 01 February 2008 10:30

Previous Topic:	About IDLffDICOM
Next Topic:	Re: county and urban shapefiles

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Fri Oct 10 04:49:38 PDT 2025

Total time taken to generate the page: 1.91942 seconds