Butterworth Filter design

[nimirope]

Hello,

I need to design a butterworth filter with following characteristics:

1. Type: Low-Pass
2. Characteristic: Butterworth
3. Cutoff-Frequency: 60 Hz
4. Tolerance level at 0 Hz : +0,1/-0,2 dB
5. Tolerance level at 60 Hz : (-3dB) +0,1/-0,3 dB
6. Slope: 24 dB/Octave
7. Tolerance level of the slope : +5/-5 dB
8. Attenuation band: -50 dB

The sample rate is 2 kHz.

I guess it must be a butterworth filter 4th-order (because the slope is 24 dB/Octave) with a low cut off frequency of 60 Hz.

But what is the attenuation band and how can I find out the tolerance levels?

Thanks for your help!

[GerdW]

Hi nimirope,

there are online resources like this or that to determine filter parameters. Have you tried them?

[nimirope]

Thank you for your help. Unfortunately I have no idea how to use the filter design tools.

Can't I use the butterworth VI like this?:

[GerdW]

Hi nimirope,

Can't I use the butterworth VI like this?

Yes sure!

But it doesn't provide all the options you want to configure…

Those webtools atleast offer some insights and ideas on how to design your filter and how to implement them. (LabVIEW also supports FIR and IIR filters!)

[nimirope]

Could you recommend me any tutorials or examples?

[nimirope]

And why doesn't the butterworth vi in labview provide all the options I need for my task?

[GerdW]

Hi nimirope,

why doesn't the butterworth vi in labview provide all the options I need for my task?

Because for "usual" requirements you don't need those settings. Filter order and cutoff frequency is most often sufficient, the other parameters are set by the filter type (aka Butterworth)…

[nimirope]

Hi GerdW,

I downloaded the digital filter design tool for labview.

Could you please tell/explain me what I have to put into the passband ripple and stopband edge frequency?

[GerdW]

Hi nimirope,

I never used that tool (or toolkit)…

what I have to put into the passband ripple and stopband edge frequency?

Passband ripple: max deviation from gain=1 in the passband (your "tolerance level at 0 Hz")

stopband edge frequency: frequency, where does the filter needs to meet the stopband attenuation