fdesign.parameq
Parametric equalizer filter specification
Compatibility
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 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 character
vector. 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 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, setGref > G0For boost:
G0 > Gp > GBW > Gst > Gref; For cut:G0 < Gp < GBW < Gst < GrefBandwidth 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');
