multistage

Multistage filter from specification object

Support for multistage filter design using the fdesign.interpolator and fdesign.decimator objects will be removed in a future release. Use the designMultistageInterpolator and the designMultistageDecimator functions, respectively.

Multistage filter design using the fdesign.lowpass object and the design function now requires you to set the SystemObject flag to true unless the resulting design is a single-stage filter and not a cascade.

For more information on how to replace your existing code, see Version History.

Syntax

msFilter = design(d,'multistage',SystemObject=true)
msFilter = design(...,filterstructure=structure,SystemObject=true)
msFilter = design(...,nstages=nstages,SystemObject=true)
msFilter = design(...,usehalfbands=hb,SystemObject=true)


Description

msFilter = design(d,'multistage',SystemObject=true) designs a multistage filter whose response you specified by the filter specification object d.

msFilter = design(...,filterstructure=structure,SystemObject=true) returns a filter with the structure specified by structure. Input argument structure is dffir by default and can also be one of the following options.

structure	Valid with These Responses
firdecim	Lowpass or Nyquist response
firtdecim	Lowpass or Nyquist response
firinterp	Lowpass or Nyquist response
lowpass	Default lowpass only

Multistage design applies to the default lowpass filter specification object and to decimators and interpolators that use either lowpass or Nyquist responses.

msFilter = design(...,nstages=nstages,SystemObject=true) specifies nstages, the number of stages to be used in the design. nstages must be an integer or auto. To allow the design algorithm to use the optimal number of stages while minimizing the cost of using the resulting filter, nstages is auto by default. When you specify an integer for nstages, the design algorithm minimizes the cost for the number of stages you specify.

msFilter = design(...,usehalfbands=hb,SystemObject=true) uses halfband filters when you set hb to true. The default value for hb is false.

Note

To see a list of the design methods available for your filter, use designmethods(hd).

Examples

Design a Multistage Interpolator

This example designs a minimum order, multistage Nyquist interpolator.

l = 15;   % Interpolation factor. Also the Nyquist band.
tw = 0.05; % Normalized transition width
ast = 40;   % Minimum stopband attenuation in dB
msMinInterp = designMultistageInterpolator(l,2,tw,ast)

msMinInterp = 
  dsp.FilterCascade with properties:

         Stage1: [1×1 dsp.FIRInterpolator]
         Stage2: [1×1 dsp.FIRInterpolator]
    CloneStages: false

filterAnalyzer(msMinInterp);

Design a multistage lowpass interpolator with an interpolation factor of 8 using the designMultistageInterpolator function.

m = 8; 
msInterp = designMultistageInterpolator(m,2);
filterAnalyzer(msInterp);

Version History

Introduced in R2011a

R2022b: Support for multistage design in fdesign.interpolator and fdesign.decimator will be removed

Support for multistage filter design using the fdesign.interpolator and fdesign.decimator objects will be removed in a future release. Use the designMultistageInterpolator and the designMultistageDecimator functions, respectively.

Update Code

This table shows how to update your code to use the equivalent functions.

Discouraged Usage	Recommended Replacement
Using the design function and passing the 'multistage' flag as an input. L = 12; % Interpolation factor TW = 2205; % Transition width Astop = 80; % Stopband attenuation Fs = 44100; % Output sample rate filtSpec = fdesign.interpolator(L,'nyquist',L,TW,Astop,Fs) filtObj = design(filtSpec,'multistage',SystemObject=true)	When you set the cost method to 'design', the function designs an optimal number of stages so that the overall implementation cost is low. filtObj = designMultistageInterpolator(L,Fs,TW,Astop,... CostMethod='design')
Using the multistage function directly. filtObj = multistage(filtSpec,SystemObject=true)
Using the design function and passing the 'multistage' flag as an input. D = 9; % Decimation factor TW = 2205; % Transition width Astop = 80; % Stopband attenuation Fs = 44100; % Input sample rate filtSpec = fdesign.decimator(D,'nyquist',D,TW,Astop,Fs) filtObj = design(filtSpec,'multistage',SystemObject=true)	When you set the cost method to 'design', the function designs an optimal number of stages so that the overall implementation cost is low. filtObj = designMultistageDecimator(D,Fs,TW,Astop,... CostMethod='design')
Using the multistage function directly. filtObj = multistage(filtSpec,SystemObject=true)

R2022b: Support for designing mfilt.cascade object using the fdesign.lowpass object has been removed

Multistage filter design using the fdesign.lowpass object and the design function now requires you to set the SystemObject flag to true unless the resulting design is single-stage filter and not a cascade. This setting generates a dsp.FilterCascade object instead of the mfilt.cascade object.

fdesignObj = fdesign.lowpass('Fp,Fst,Ap,Ast',...
0.1,0.12,0.1,1e-4,'linear');
FIRInterpObj = multistage(fdesignObj,SystemObject=true)

FIRInterpObj = 

  dsp.FilterCascade with properties:

         Stage1: [1×1 dsp.FIRDecimator]
         Stage2: [1×1 dsp.FIRDecimator]
         Stage3: [1×1 dsp.FIRDecimator]
         Stage4: [1×1 dsp.FIRInterpolator]
         Stage5: [1×1 dsp.FIRInterpolator]
         Stage6: [1×1 dsp.FIRInterpolator]
    CloneStages: true