Why are filter coeffiecients of Notch filter design at filterDesigner App and notch-peak block(simulink) are different ?

I have a question,

Why are filter coeffiecients of Notch filter design at filterDesigner App and notch-peak block(simulink) are different ?

-------------------------------------------------------

Specification of desired notch filter

fs = 100 Hz

fc = 10 Hz

bw = 2 Hz

Filter strucure : CA lattice

------------------------------------------------------

When using filterDesigner App

designed as shown in below and its filter coefficients .

But when using Notch-Peak block in simulink, I get this.

One of Allpass2.Lattice(2) is [0.881618592363188957605757423152681440115] and the other one is [0.937958302720203862534731342748273164034 ].

Why are the two coefficients different?

I think designing the two filters are using the same specification, What am I missing?

Answer 1

[Shreeya]

Hello,

I understand that you are receiving different filter coefficients when using the filter designer app and the notch filter Simulink block. Since this block brings the functionality of “dsp.NotchPeakFilter()” function in Simulink, I have tried to reproduce the problem using this function and the filter designer app in R2023a with the following inferences:

• In the filter designer app, the badwidth is determined by the attenuation value specified in the "Apass" edit box. By default, this dB value is 1, i.e. the notch/peak band is measured at level -1dB
• In contrast, the "dsp.NotchPeakFilter" does not allow to specify the band attenuation. Rather, it defaults to 10*log10(1/2), which is nearly -3dB.

To get the exact same coefficients in the filter designer app, you can set the "Apass" value to 10*log10(1/2).

Hope this helps!