User`s guide

Filtering Data
filter = idm
filter = {num,den}
filter = {A,B,C,D}
idm
is a SISO idmodel or LTI object. For more information about LTI objects,
see the Control System Toolbox documentation.
{num,den} defines the filter as a transfer function as a cell array of numerator
and denominator filter coefficients.
{A,B,C,D} is a cell array of SISO state-space matrices.
Specifically for frequency-domain data, you specify the frequency response
of the filter:
filter = Wf
Here, Wf is a vector of real or complex values that define the filter
frequency response, where the inputs and outputs of
data at frequency
data.Frequency(kf) are multip lied by Wf(kf). Wf is a column v ector with
the length equal to the number of frequencies in
data.
When
data contains several experiments, Wf is a cell array with the length
equal to the number of experiments in
data.
Causal and Noncausal Filters
For time-domain data, the filteringiscausalbydefault. Causalfilters
typically introduce a phase shift in the results. To use a noncausal zero-phase
filter (corresponding to
filtfilt in the Sig nal Processing T o o lb ox product),
specify a third argument in
idfilt:
fdata = idfilt(data,filter,'noncausal')
For frequen cy-do m ain data, th e sign a ls are multiplied by the frequency
response of the filter. With the filters defined as passband fi lters, thi s
calculation gives ideal, zero-phase filtering (“brick wall fi lters”). Frequencies
that have been assign ed zero weight by the filter (outside the passband or
via frequency response) are removed.
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