Filter Design Toolbox

iirpeak

Design a second-order IIR peak or resonator digital filter

Syntax

• [num,den] = iirpeak(w0,bw)
  [num,den] = iirpeak(w0,bw,ab)
  

Description

[num,den] = iirpeak(w0,bw) eturns a second-order digital peaking filter with the peak located at w0, and with the bandwidth at the +3dB point set to bw. To design the filter, w0 must meet the condition 0.0 < w0 < 1.0, where 1.0 corresponds to  radians per sample in the frequency range.

The quality factor (Q factor) q for the filter is related to the filter bandwidth by q = ₀/bw where ₀ is w0 the signal frequency to boost.

[num,den] = iirpeak(w0,bw,ab) returns a digital peaking filter whose bandwidth, bw, is specified at a level of +ab decibels. Including the optional input argument ab lets you specify the magnitude response bandwidth at a level that is not the default +3dB point, such as +6 dB or 0 dB.

Examples

Design and plot an IIR peaking filter that boosts the frequency at 1.75 Khz in a signal and has bandwidth of 500 Hz at the -3 dB point:

• fs = 10000; wo = 1750/(fs/2);  bw = 500/(fs/2);
  [b,a] = iirpeak(wo,bw);
  fvtool(b,a);
  

Shown in the next plot, the peak filter has the desired gain and bandwidth at 1.75 KHz.

See Also

gremez, iircomb, iirnotch

iirnotch

iirpowcomp