Notch Filter

A Notch Filter is also known as a Band Stop filter or Band Reject Filter. The filter passes the signals above and below a specified frequency band unaltered. This band is called the stop band frequency range. And it attenuates (‘rejects’) the frequencies within this range to very low levels.

IIR notch filter frequency response

Hd = notch (Fo, BW, DFormat)

IIR notch filter design, defined as:

\(H(z)=\frac{1-2cos⁡ w_o z^{-1}+z^{-2}}{1-2rcos⁡ w_o z^{-1}+ r^2 z^{-2}}\)

where, \(w_o=\frac{2\pi f_o}{f_s}\) controls the centre frequency, \(f_o\) of the notch, and \( r=1-\frac{\pi BW}{f_s} \)controls the bandwidth (-3dB point) of the notch.

Fo: centre frequency of the notch

BW: Bandwidth (-3dB point) of the notch. Where, \(BW ≤ \frac{F_o}{4}\)

DFormat: allows you to specify the display format of resulting digital filter object.

symbolic Display a symbolic representation of the filter object. If the order > 10, the symbolic display option will be overridden and set to numeric
numeric Display a matrix representation of the filter object
void Create a filter object, but do not display output


ClearH1;  // clear primary filter from cascade
ShowH2DM;   // show DM on chart

interface BW={5,40,2,10};



Num = getnum(Hd); // define numerator coefficients
Den = getden(Hd); // define denominator coefficients
Gain = getgain(Hd); // define gain

See also

bessel / butter / cheby1 / cheby2 / ellip / arbmagphase / cplxfreqshift / dcremover / notch / peaking