Re: Newbie type "What if's"
- From: Richard Owlett <rowlett@xxxxxxxxxxxxx>
- Date: Thu, 17 Jul 2008 05:14:25 -0500
Rune Allnor wrote:
On 16 Jul, 20:00, Richard Owlett <rowl...@xxxxxxxxxxxxx> wrote:
I've been reading Lyons' Chapters 4&5 (FIR and IIR filters).
Some questions crossed my mind triggered by what I read.
They didn't correspond to where Rick wants to take the reader ;)
1. What "kind(s)" of filter(s) would have a strictly real valued impulse
response.
2. Starting with the IIR topology of Fig 6-3, what "kind(s)" of filter
response(s) would result from strictly real values for the feedback and
feedforward coefficients a(n) and b(n)?
The answer to both your questions is that most people will never see
a case where the coeffcients are *complex*. Even when complex
coefficients
might be useful, most people use real IQ filters.
Rune
Maybe I have a better feel for "how things are" than I thought. As to the first question, I was reasoning along the line that there should be a duality between a time delay and a phase angle. I had also been reading that to realize an arbitrarily shaped frequency response yo Fourier Transform it to get the required impulse response. I'll experiment with the frequency responses that interest me, keep only the real part of the resulting impulse response and see if the result is "good enough"
To what does "real IQ filters" refer. I don't find any thing in index of either rick Lyons' or Steve Smith's books. Google was no help.
The closest I came was a quaduture modulation technique.
.
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