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help

Help for design method with filter specification

Syntax

help(d,'designmethod')

Description

help(d,'designmethod') displays help in the command window for the design algorithm designmethod for the current specifications of the filter specification object d. designmethod must be one of the design algorithms returned by designmethods for d, the design object.

Examples

Get specific help for designing lowpass Butterworth filters. The first lowpass filter uses the default specification 'Fp,Fst,Ap,Ast' and returns help text specific to the specification.

d = fdesign.lowpass;
designmethods(d)

Design Methods for class fdesign.lowpass (Fp,Fst,Ap,Ast):

butter
cheby1
cheby2
ellip
equiripple
ifir
kaiserwin
multistage

help(d,'butter')

DESIGN Design a Butterworth IIR filter.
HD = DESIGN(D, 'butter') designs a Butterworth filter specified 
by the FDESIGN object D.
 
HD = DESIGN(..., 'FilterStructure', STRUCTURE) returns a filter 
with the structure STRUCTURE.  STRUCTURE is 'df2sos' by default 
and can be any of the following.

'df1sos'
'df2sos'
'df1tsos'
'df2tsos'
 
HD = DESIGN(..., 'MatchExactly', MATCH) designs a Butterworth 
filter and matches the frequency and magnitude specification for 
the band MATCH exactly. The other band will exceed the 
specification.  MATCH can be 'stopband' or 'passband' and is 
'stopband' by default.
 
% Example #1 - Compare passband and stopband MatchExactly.
h     = fdesign.lowpass('Fp,Fst,Ap,Ast', .1, .3, 1, 60);
Hd    = design(h, 'butter', 'MatchExactly', 'passband');
Hd(2) = design(h, 'butter', 'MatchExactly', 'stopband');
       
% Compare the passband edges in FVTool.
fvtool(Hd);
axis([.09 .11 -2 0]);

Note the discussion of the MatchExactly input option. When you use a design object that uses a different specification, such as 'N,F3dB', the help content for the butter design method changes.

In this case, the MatchExactly option does not appear in the help because it is not an available input argument for the specification 'N,F3dB'.

d=fdesign.lowpass('N,F3dB')
 
d =
                Response: 'Lowpass'                       
          Specification: 'N,F3dB'                        
            Description: {'Filter Order';'3dB Frequency'}
    NormalizedFrequency: true                            
            FilterOrder: 10                              
                   F3dB: 0.5                             
                                                         
designmethods(d)

Design Methods for class fdesign.lowpass (N,F3dB):

butter

help(d,'butter

DESIGN Design a Butterworth IIR filter.

HD = DESIGN(D, 'butter') designs a Butterworth filter specified by the FDESIGN object D.

HD = DESIGN(..., 'FilterStructure', STRUCTURE) returns a filter with the structure STRUCTURE. STRUCTURE is 'df2sos' by default and can be any of the following.

'df1sos'

'df2sos'

'df1tsos'

'df2tsos'

% Example #1 - Design a lowpass Butterworth filter in the DF2TSOS structure.

h = fdesign.lowpass('N,F3dB');

Hd = design(h, 'butter', 'FilterStructure', 'df2tsos');

Introduced in R2011a

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