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Topic: Bessel Filter cutoff frequ.
Replies: 1   Last Post: Aug 29, 1996 10:58 AM

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Joerg Beilharz

Posts: 1
Registered: 12/11/04
Bessel Filter cutoff frequ.
Posted: Aug 29, 1996 2:19 AM
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Hi folks,

Th. Krauss wrote two bessel filter functions: besselap and besself,
where besself just invokes besselap and lp2lp (lp2bp ...) in order to
transform cutoff frequencies, etc.

besselap is not more than a lookup tabel of filter coefficients. But,
as stated in the help text, 3 dB cutoff frequency decreases as the
order of the filter increases. This actually is pretty annoying ...
(yes, you won't get correct cutoff frequencies with besself)

Where do the coefficients come from?
Why are they so odd?
Any possibility to solve the problem easily?

Remark: I know of some books listing bessel filter coefficients, which
result in correct prototypes, i.e. omega_cutoff=1 independent of N.
Therefore I'd like to get my questions answered for academical
reasons only!


Joerg Beilharz

TU Berlin, Sekr. E2 Phone: +49 30 314-24893
Inst. Mess- u. Automatisierungstechnik Fax: +49 30 314-25717
Einsteinufer 19, D-10587 Berlin, Germany

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