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"Time revresion technique"

Started by shamganth August 27, 2003
sir,
 iam trying to implement Linear phase IIR filter. To acheieve Linear
phase in IIR filter we have the main technique of Time reversion of
the section. If anyone is doing in the same please reply.
thanks in advance.
On 27 Aug 2003 03:17:08 -0700, shamganth@rediffmail.com (shamganth)
wrote:

>sir, > iam trying to implement Linear phase IIR filter. To acheieve Linear >phase in IIR filter we have the main technique of Time reversion of >the section. If anyone is doing in the same please reply. >thanks in advance.
Hi, Ah, you mean "time reversal". That's a *BIG* difference from the way you worded your question in your earlier post. Andor already answered your question by saying you should review MATLAB's "filtfilt()" function. Look in the 'Signal Processing Toolbox' manual. It'll answer all your questions. Also, check out the thread: Subject: A fundamental question on 0-phase filter Date: 19 Aug 2003 07:41:44 -0700 [-Rick-]
shamganth wrote:
> > sir, > iam trying to implement Linear phase IIR filter. To acheieve Linear > phase in IIR filter we have the main technique of Time reversion of > the section. If anyone is doing in the same please reply. > thanks in advance.
Search http://www.groops.google.com for a recent thread on this subject. Be aware that this is difficult in quasi real time. Jerry Also: In article s68d6eshvmp.fsf@mango.itee.uq.edu.au, Peter J. Kootsookos at p.kootsookos@remove.ieee.org wrote on 08/26/2003 19:00:
> allnor@tele.ntnu.no (Rune Allnor) writes: > >> p.kootsookos@remove.ieee.org (Peter J. Kootsookos) wrote in message >> news:<s68vfsl113n.fsf@mango.itee.uq.edu.au>... >>> shamganth@rediffmail.com (shamganth) writes: >>> >>>> iam doing my postgraduation in communication in south india at Anna >>>> University. Iam doing my project in Linear phase IIR filters. I have >>>> the base materials for Linear phase iir filters. >>> >>> Do the base materials include some philosopher's stone? >> >> That's a succint formulation of my immediate reaction... I always thought >> that "[causal] IIR filter" and "linear phase" were contradicions in terms? > > Yes, that's always my immediate reaction. > >> While I haven't checked out the Clements & Pease paper, I don't understand >> what RBJ is talking about in the mentioned link, when he says "Truncated >> IIR". Isn't that, by definition, a FIR structure?
well, it *is* an FIR. what you mean be "structure" might affect my answer. the term "Truncated IIR" is from Julius Smith as referened by Peter below. a TIIR is an FIR that has some structure that would remind one of an IIR. the simplest example of a TIIR is the one of a moving average filter. there are two ways of implementing it. one is with the straight forward FIR structure in which all coefs are 1/N (N is the number of samples getting averaged). the other structure is with a digital integrator but where the input has a delay line and adder that will subtract x[n-N] from the integrator input. not every TIIR is linear phase. some of them require cascading with one that has the opposite sense of decay or it requires segmentation, time-reversing the segment, TIIRing with an identical filter, flipping the result back around in time, and overlap-adding the result. it's a mess, but it's how you make a nearly IIR filter act with linear phase in a real-time app.
>> For that matter, why would anyone want to make a linear phase IIR?
i guess so that all frequencies are delayed equally.
>> Isn't it way easier to stick with the good ol' FIR?
usually it is. but if the number of taps are large, it's not always cheaper than the Truncated IIR approach.
>> Or am I missing something? > > Effectively, you are correct, except that the implementation is IIR > and you just stop the IIR after a certain time. > > Julius O. Smith has some stuff on his web-site: > > http://ccrma-www.stanford.edu/~jos/HornModeling/Truncated_Infinite_Impulse_Res > ponse.html > > Ciao,
can you guys down-under see Mars as well as us guys? it's even a little cloudy and i can see it really well. r b-j -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;