Filter Design Toolbox™

fdesign.parameq - Parametric equalizer filter specification

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 ,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:

• F0 — Center Frequency

• 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

• Flow - Lower Frequency at Gain GBW

• Fhigh - Higher Frequency at Gain GBW

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)

The magnitude response is shown in the following figure.

fdesign.octave

fdesign.peak