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fdesign.isinclp

Inverse sinc lowpass filter specification

Syntax

d = fdesign.isinclp
d = fdesign.isinclp(spec)
d = fdesign.isinclp(spec,specvalue1,specvalue2,...)
d = fdesign.isinclp(specvalue1,specvalue2,specvalue3,specvalue4)
d = fdesign.isinclp(...,Fs)
d = fdesign.isinclp(...,MAGUNITS)

Description

d = fdesign.isinclp constructs an inverse sinc lowpass filter specification object d, applying default values for the default specification string, 'Fp,Fst,Ap,Ast'.

d = fdesign.isinclp(spec) constructs object d and sets its 'Specification' to spec. Entries in the spec string represent various filter response features, such as the filter order, that govern the filter design. Valid entries for spec are shown below. The strings are not case sensitive.

  • 'Fp,Fst,Ap,Ast' (default spec)

  • 'N,Fc,Ap,Ast'

  • 'N,Fp,Ap,Ast'

  • 'N,Fp,Fst'

  • 'N,Fst,Ap,Ast'

The string entries are defined as follows:

  • Ast — attenuation in the stopband in decibels (the default units). Also called Astop.

  • Ap — amount of ripple allowed in the passband in decibels (the default units). Also called Apass.

  • Fp — frequency at the start of the passband. Specified in normalized frequency units. Also called Fpass.

  • Fst — frequency at the end of the stopband. Specified in normalized frequency units. Also called Fstop.

  • N — filter order.

The filter design methods that apply to an inverse sinc lowpass filter specification object change depending on the Specification string. Use designmethods to determine which design method applies to an object and its specification string.

d = fdesign.isinclp(spec,specvalue1,specvalue2,...) constructs an object d and sets its specifications at construction time.

d = fdesign.isinclp(specvalue1,specvalue2,specvalue3,specvalue4) constructs an object d assuming the default Specification property string 'Fp,Fst,Ap,Ast', using the values you provide in specvalue1,specvalue2, specvalue3, and specvalue4.

d = fdesign.isinclp(...,Fs) adds the argument Fs, specified in Hz to define the sampling frequency to use. In this case, all frequencies in the specifications are in Hz as well.

d = fdesign.isinclp(...,MAGUNITS) specifies the units for any magnitude specification you provide in the input arguments. MAGUNITS can be one of

  • 'linear' — specify the magnitude in linear units

  • 'dB' — specify the magnitude in dB (decibels)

  • 'squared' — specify the magnitude in power units

When you omit the MAGUNITS argument, fdesign assumes that all magnitudes are in decibels. Note that fdesign stores all magnitude specifications in decibels (converting to decibels when necessary) regardless of how you specify the magnitudes.

The design method of fdesign.isinclp implements a filter with a passband magnitude response equal to:

H(ω)=sinc(Cω)P

You can control the values of the sinc frequency factor, C, and the sinc power, P, using the 'SincFrequencyFactor' and 'SincPower' options in the design method. 'SincFrequencyFactor' and 'SincPower' default to 0.5 and 1 respectively.

Examples

Pass the specifications for the default specification — 'Fp,Fst,Ap,Ast' — as input arguments to the specifications object.

d = fdesign.isinclp(.4,.5,.01,40);
hd = design(d,'equiripple');
fvtool(hd);

Design a 50th order inverse sinc lowpass filter. Set the sinc frequency factor to 0.25 and the sinc power to 16 to achieve a magnitude response in the passband of the form H(w) = sinc(0.25*w)^(-16) .

 d = fdesign.isinclp('N,Fp,Fst',50,.4,.5);
 Hd = design(d,'SincFrequencyFactor',0.25,'SincPower',16);
 fvtool(Hd, 'MagnitudeDisplay', 'Magnitude');

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