T. P. Traitement du Signal Maîtrise E.E.A. - LASC

Accessing Filter Parameters
Accessing Filter Parameters
You can access filter parameters in the following two ways.
• “Accessing Filter Parameters in a Saved Filter”
• “Accessing Parameters in a Saved Spectrum”
Accessing Filter Parameters in a Saved Filter
The MATLAB structures created by SPTool have several associated fields,
many of which are also MATLAB structures. See the MATLAB documentation
for general information about MATLAB structures.
For example, after exporting a filter filt1 to the MATLAB workspace, type
filt1
to display the fields of the MATLAB filter structure. The tf, Fs, and specs
fields of the structure contain the information that describes the filter.
The tf Field: Accessing Filter Coefficients
The tf field is a structure containing the transfer function representation of
the filter. Use this field to obtain the filter coefficients;
• filt1.tf.num contains the numerator coefficients.
• filt1.tf.den contains the denominator coefficients.
The vectors contained in these structures represent polynomials in descending
powers of z. The numerator and denominator polynomials are used to specify
the transfer function
Hz ()
where:
Bz () b( 1) + b( 2)z ----------
– 1 + L + bnb ( + 1)z = = -----------------------------------------------------------------------------------------
– m
Az () a( 1) + a( 2)z – 1 + L + ana ( + 1)z – n
• b is a vector containing the coefficients from the tf.num field.
• a is a vector containing the coefficients from the tf.den field.
• m is the numerator order.
• n is the denominator order.
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