iirnotch

(To be removed) Second-order IIR notch filter

The iirnotch function will be removed in a future release. Use the designNotchPeakIIR function instead. For more information on how to update your existing code, see Version History.

Syntax

[num,den] = iirnotch(w0,bw)

[num,den] = iirnotch(w0,bw,ab)

Description

[num,den] = iirnotch(w0,bw) returns the numerator coefficients, num, and the denominator coefficients, den, of the digital notching filter with the notch located at 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/bw, where w0 is the notch frequency.

[num,den] = iirnotch(w0,bw,ab) returns the digital notching filter whose bandwidth, bw, is specified at a level of –ab decibels.

Examples

Design IIR Notch Filter Using iirnotch

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);

Visualize the magnitude response.

The notch filter has the desired bandwidth with the notch located at 60 Hz, or $$0.4\pi$$ radians per sample.

filterAnalyzer(b,a)

Input Arguments

w0 — Notch frequency

positive scalar

Notch frequency, specified as a positive scalar in the range (0.0, 1.0), where 1.0 corresponds to π radians per sample in the frequency range.

Data Types: single | double

bw — 3 dB bandwidth

positive scalar

Bandwidth at the –3 dB point, specified as a positive scalar in the range (0.0, 1.0).

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

Data Types: single | double

ab — Custom decibel level

real scalar

Custom decibel level, –ab, at which the filter has a bandwidth of bw. 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 (10log₁₀(1/2)).

Data Types: single | double

Output Arguments

num — Numerator coefficients

row vector

Numerator coefficients of the designed notch filter, returned as a row vector.

Data Types: double

den — Denominator coefficients

row vector

Denominator coefficients of the designed notch filter, returned as a row vector.

Data Types: double

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Version History

Introduced in R2011a

R2024a: iirnotch will be removed

The iirnotch function will be removed in a future release. Existing instances of the function continue to run. For new code, use the designNotchPeakIIR function instead.

Update Code

This table shows how the function is typically used and explains how to update the existing code to use the designNotchPeakIIR function.

Discouraged Usage	Recommended Replacement
Notch frequency is $$0.4\pi$$ radians per sample. Quality factor is 35. wo = 60/(300/2); bw = wo/35; [b,a] = iirnotch(wo,bw);	[b,a] = designNotchPeakIIR(CenterFrequency=wo,... Bandwidth=bw,Response="notch"); or [b,a] = designNotchPeakIIR(CenterFrequency=wo,... QualityFactor=35,Response="notch");