On Fri, 10 Oct 2008 02:35:04 -0700 (PDT), Andor
<andor.bariska@[EMAIL PROTECTED]
> wrote:
>robert bristow-johnson wrote:
>> On Oct 9, 5:21 pm, "sauwen" <sauwen...@[EMAIL PROTECTED]
> wrote:
>>
>> > Hi all. Does anyone know how to change the width of a feedback comb
>> > filter's teeth? From the general idea on wikipedia, it seems like it
is
>> > only possible to change the delays and the gain.
>>
>> when you have a feedback comb filter (or even a feed-forward comb
>> filter), try to imagine replacing the delay element, z^-N, with a
>> quantitatively different delay element, z^-1. then with that
>> feedback, you have a simple LPF where, depending on the feedback gain,
>> you can get an idea of how wide this single tooth is. now replace
>> z^-1 with z^-N and you will see that your tooth is scrunched by a
>> factor of 1/N and there are N of these teeth from -Nyquist to just
>> under +Nyquist.
>>
>> does that help you figger it out?
>
>But what to do if you have a comp filter where you are interested in N
>notches and now want to sharpen those notches without increasing their
>number? FIR filter sharpening to the rescue!
>
>Matthew's original DSP Guru article is now published (well done
>Matthew, whereever you are!) but still downloadable:
>
>http://www.dsprelated.com/showabstract/62.php
>
>Regards,
>Andor
Hi Andor,
That's a good point you're making here.
Two items:
[1] I don't think Donadio's "filter sharpening" article
was ever on the dspguru.com website. It was, however,
in the IEEE Sig. Proc. Magazine's "DSP Tip & Tricks"
column in Sept. 2003 (pages 61-63). A slightly expanded
version of that article later became Chapoter 1 of the
book "Streamlining Digital Signal Processing, a Tricks
of the Trade Guidebook" (published by Wiley & Sons and
the IEEE). That PDF file, that you cited, is the
book's Chapter 1.
[2] In the first sentence of the last paragraph on
page 6 of the PDF file, the phrase "half-power" should
be changed to "half-amplitude".
Regards,
[-Rick-]
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