Second-order IIR notch filter
returns the numerator coefficients,
den] = iirnotch(
num, and the denominator
den, of the digital notching filter with the notch
w0 and the bandwidth at the –3 dB point set to
bw. To design the filter,
w0 must meet the
condition 0.0 <
w0 < 1.0, where 1.0 corresponds to π radians per
sample in the frequency range.
The quality factor (Q factor) q for the filter is related to the
filter bandwidth by q =
w0 is the notch frequency.
returns the digital notching filter whose bandwidth,
den] = iirnotch(
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 –3 dB point, such as –6 dB or 0 dB. If not specified,
ab defaults to the –3 dB width
Design and plot an IIR notch filter that removes a 60 Hz tone (f0) from a signal at 300 Hz (fs). For this example, set the Q factor for the filter to 35 and use it to specify the filter bandwidth.
wo = 60/(300/2); bw = wo/35; [b,a] = iirnotch(wo,bw);
The notch filter has the desired bandwidth with the notch located at 60 Hz, or radians per sample. Compare this plot to the comb filter plot shown for
w0— Notch frequency
Notch frequency, specified as a positive scalar in the range 0.0 <
w0 < 1.0, where 1.0 corresponds to π radiance per sample in
the frequency range.
bw— 3 dB bandwidth
Bandwidth at the –3 dB point, specified as a positive scalar in the range 0.0 <
w0 < 1.0.
num— Numerator coefficients
Numerator coefficients of the designed notch filter, returned as a row vector.
den— Denominator coefficients
Denominator coefficients of the designed notch filter, returned as a row vector.
Usage notes and limitations:
All inputs must be constant. Expressions or variables are allowed if their values do not change.