designmethods

Methods available for designing filter from specification object

Description

example

methods = designmethods(designSpecs,'SystemObject',true) returns the available design methods for designing filter System objects for the filter specification object, designSpecs.

methods = designmethods(designSpecs,'default') returns the default design method for the filter specification object designSpecs.

methods = designmethods(designSpecs,TYPE,'SystemObject',true) returns the TYPE design methods for the filter specification object, designSpecs. TYPE can be either 'FIR' or 'IIR'.

methods = designmethods(designSpecs,'full','SystemObject',true) returns the full name for each of the available design methods. For example, designmethods with the 'full' argument returns Butterworth for the butter method.

Examples

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Construct a lowpass filter design specification object and determine the valid design methods.

designSpecs = fdesign.lowpass('Fp,Fst,Ap,Ast',500,600,0.5,60,1e4);
methods = designmethods(designSpecs,'SystemObject',true)
methods = 8x1 cell array
    {'butter'    }
    {'cheby1'    }
    {'cheby2'    }
    {'ellip'     }
    {'equiripple'}
    {'ifir'      }
    {'kaiserwin' }
    {'multistage'}

Use help to get more information on the Chebyshev type I design method.

help(designSpecs,methods{2})
 DESIGN Design a Chebyshev type I iir filter.
    HD = DESIGN(D, 'cheby1') designs a Chebyshev type I filter specified by the
    FDESIGN object D, and returns the DFILT/MFILT object HD.
 
    HD = DESIGN(D, ..., 'SystemObject', true) implements the filter, HD,
    using a System object instead of a DFILT/MFILT object.
 
    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'
    'cascadeallpass'
    'cascadewdfallpass'
 
    Some of the listed structures may not be supported by System object
    filters. Type validstructures(D, 'cheby1', 'SystemObject', true) to
    get a list of structures supported by System objects.
 
    HD = DESIGN(..., 'MatchExactly', MATCH) designs a Chebyshev type I
    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 'passband' by default.
 
    HD = DESIGN(..., 'SOSScaleNorm', NORM) designs an SOS filter and scales
    the coefficients using the P-Norm NORM. NORM can be either a 
    discrete-time-domain norm or a frequency-domain norm. Valid time-domain 
    norms are 'l1','l2', and 'linf'. Valid frequency-domain norms are 
    'L1','L2', and 'Linf'. Note that L2-norm is equal to l2-norm 
    (Parseval's theorem) but the same is not true for other norms.
    
    The different norms can be ordered in terms of how stringent they are 
    as follows: 'l1' >= 'Linf' >= 'L2' = 'l2' >= 'L1' >= 'linf'.
    Using the most stringent scaling, 'l1', the filter is the least prone 
    to overflow, but also has the worst signal-to-noise ratio. Linf-scaling is 
    the most commonly used scaling in practice.
    
    Scaling is turned off by default, which is equivalent to setting
    SOSScaleNorm = ''.
 
    HD = DESIGN(..., 'SOSScaleOpts', OPTS) designs an SOS filter and scales
    the coefficients using an FDOPTS.SOSSCALING object OPTS.  Scaling options 
    are:
    Property                Default     Description/Valid values
    ---------               -------     ------------------------
    'sosReorder'            'auto'      Reorder section prior to scaling.
                                        {'auto','none','up','down','lowpass',
                                         'highpass','bandpass','bandstop'}
    'MaxNumerator'          2           Maximum value for numerator coefficients
    'NumeratorConstraint'   'none'      {'none', 'unit', 'normalize','po2'}
    'OverflowMode'          'wrap'      {'wrap','saturate'}
    'ScaleValueConstraint'  'unit'      {'unit','none','po2'}
    'MaxScaleValue'         'Not used'  Maximum value for scale values
    
    When sosReorder is set to 'auto', the sections will be automatically
    reordered depending on the response type of the design (lowpass,
    highpass, etc.).
    
    Note that 'MaxScaleValue' will only be used when 'ScaleValueConstraint'
    is set to something other than 'unit'. If 'MaxScaleValue' is set to a
    number, the 'ScaleValueConstraint' will be changed to 'none'. Further,
    if SOSScaleNorm is off (as it is by default), then all the SOSScaleOpts
    will be ignored.
 
    For more information about P-Norm and scaling options see help for DFILT\SCALE.
 
    % Example #1 - Compare passband and stopband MatchExactly.
       h     = fdesign.lowpass('Fp,Fst,Ap,Ast', .1, .3, 1, 60);
       Hd    = design(h, 'cheby1', 'MatchExactly', 'passband');
       Hd(2) = design(h, 'cheby1', 'MatchExactly', 'stopband');
       
       % Compare the passband edges in FVTool.
       fvtool(Hd);
       axis([.09 .11 -2 0]);
 

Input Arguments

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Filter specification object, specified as one of the fdesign functions.

Impulse response of the designed filter, specified as 'FIR' or 'IIR'. When not specified, the function outputs design methods which support both 'FIR' and 'IIR' response types.

Example: designmethods(designSpecs,'FIR','SystemObject',true)

Output Arguments

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Available design methods, returned as a cell array. Each cell contains the name of the method and is determined by the arguments input to the function.

Introduced in R2009a