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There is a BESSEL filter generator in Matlab.
Looks like an exponential moving average for the 1-st
order. The B vector has all components equal to zero
except for the last one for Bessel filter.
My understanding is that Bessel filter best preserves
the waveform and has little ringing and overshoot. It
is interesting what one gets if he cascades Bessel
filters... T3 is cascaded EMA's, but EMA is 1-st order
Bessel filter. What about higher order?
Sergey Efremov
help besself
BESSELF Bessel analog filter design.
[B,A] = BESSELF(N,Wn) designs an N'th order
lowpass analog
Bessel filter and returns the filter coefficients
in length
N+1 vectors B and A. The cut-off frequency Wn
must be
greater than 0.
If Wn is a two-element vector, Wn = [W1 W2],
BESSELF returns an
order 2N bandpass filter with passband W1 < W <
W2.
[B,A] = BESSELF(N,Wn,'high') designs a highpass
filter.
[B,A] = BESSELF(N,Wn,'stop') is a bandstop filter
if Wn = [W1 W2].
When used with three left-hand arguments, as in
[Z,P,K] = BESSELF(...), the zeros and poles are
returned in
length N column vectors Z and P, and the gain in
scalar K.
When used with four left-hand arguments, as in
[A,B,C,D] = BESSELF(...), state-space matrices are
returned.
See also BESSELAP, BUTTER, CHEBY1, CHEBY2, FREQZ
and FILTER.
help filter
FILTER One-dimensional digital filter.
Y = FILTER(B,A,X) filters the data in vector X
with the
filter described by vectors A and B to create the
filtered
data Y. The filter is a "Direct Form II
Transposed"
implementation of the standard difference
equation:
a(1)*y(n) = b(1)*x(n) + b(2)*x(n-1) + ... +
b(nb+1)*x(n-nb)
- a(2)*y(n-1) - ... -
a(na+1)*y(n-na)
If a(1) is not equal to 1, FILTER normalizes the
filter
coefficients by a(1).
When X is a matrix, FILTER operates on the columns
of X. When X
is an N-D array, FILTER operates along the first
non-singleton
dimension.
[Y,Zf] = FILTER(B,A,X,Zi) gives access to initial
and final
conditions, Zi and Zf, of the delays. Zi is a
vector of length
MAX(LENGTH(A),LENGTH(B))-1 or an array of such
vectors, one for
each column of X.
FILTER(B,A,X,[],DIM) or FILTER(B,A,X,Zi,DIM)
operates along the
dimension DIM.
See also FILTER2, FILTFILT (in the Signal
Processing Toolbox).
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