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fdesign.parameq

Parametric equalizer filter specification

    Note:   The fdesign.parameq function will be removed from DSP System Toolbox™ in a future release. Existing instances of the function continue to run. For new code, use the fdesign.parameq function from Audio System Toolbox™ instead.

Syntax

d = fdesign.parameq(spec, specvalue1, specvalue2, ...)
d = fdesign.parameq(... fs)

Description

d = fdesign.parameq(spec, specvalue1, specvalue2, ...) constructs a parametric equalizer filter design object, where spec is a non-case sensitive specification string. The choices for spec are as follows:

  • 'F0, BW, BWp, Gref, G0, GBW, Gp' (minimum order default)

  • 'F0, BW, BWst, Gref, G0, GBW, Gst'

  • 'F0, BW, BWp, Gref, G0, GBW, Gp, Gst'

  • 'N, F0, BW, Gref, G0, GBW'

  • 'N, F0, BW, Gref, G0, GBW, Gp'

  • 'N, F0, Fc, Qa, G0'

  • 'N, F0, Fc, S, G0'

  • 'N, F0 ,BW, Gref, G0, GBW, Gst'

  • 'N, F0, BW, Gref, G0, GBW, Gp, Gst'

  • 'N, Flow, Fhigh, Gref, G0, GBW'

  • 'N, Flow, Fhigh, Gref, G0, GBW, Gp'

  • 'N, Flow, Fhigh, Gref, G0, GBW, Gst'

  • 'N, Flow, Fhigh, Gref, G0, GBW, Gp, Gst'

where the parameters are defined as follows:

  • BW — Bandwidth

  • BWp — Passband Bandwidth

  • BWst — Stopband Bandwidth

  • Gref — Reference Gain (decibels)

  • G0 — Center Frequency Gain (decibels)

  • GBW — Gain at which Bandwidth (BW) is measured (decibels)

  • Gp — Passband Gain (decibels)

  • Gst — Stopband Gain (decibels)

  • N — Filter Order

  • F0 — Center Frequency

  • Fc— Cutoff frequency

  • Fhigh - Higher Frequency at Gain GBW

  • Flow - Lower Frequency at Gain GBW

  • Qa-Quality Factor

  • S-Slope Parameter for Shelving Filters

Regardless of the specification string chosen, there are some conditions that apply to the specification parameters. These are as follows:

  • Specifications for parametric equalizers must be given in decibels

  • To boost the input signal, set G0 > Gref; to cut, set Gref > G0

  • For boost: G0 > Gp > GBW > Gst > Gref; For cut: G0 < Gp < GBW < Gst < Gref

  • Bandwidth must satisfy: BWst > BW > BWp

d = fdesign.parameq(... fs) adds the input sampling frequency. Fs must be specified as a scalar trailing the other numerical values provided, and is assumed to be in Hz.

Examples

Design a Chebyshev Type II parametric equalizer filter that cuts by 12 dB:

 d = fdesign.parameq('N,Flow,Fhigh,Gref,G0,GBW,Gst',...
       4,.3,.5,0,-12,-10,-1);
 Hd = design(d,'cheby2');
 fvtool(Hd)

Design a 4th order audio lowpass (F0 = 0) shelving filter with cutoff frequency of Fc = 0.25, quality factor Qa =10, and boost gain of G0 = 8 dB:

d = fdesign.parameq('N,F0,Fc,Qa,G0',4,0,0.25,10,8);
Hd = design(d);
fvtool(Hd)

Design 4th-order highpass shelving filters with S=1.5 and S=3:

N=4;
F0 = 1;
Fc = .4; % Cutoff Frequency
G0 = 10;
S = 1.5;
S2=3;
f = fdesign.parameq('N,F0,Fc,S,G0',N,F0,Fc,S,G0);
h1 = design(f);
f.S=3;
h2=design(f);
hfvt=fvtool([h1 h2]);
set(hfvt,'Filters',[h1 h2]);
legend(hfvt,'S=1.5','S=3');

See Also

Introduced in R2011a

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