6 dB/octave highpass Butterworth problem

[TomTomTomTomTom]

Hello!

I want to make pre-emphasis filter. I know some specifications:

First order Butterworth, high-pass with cutoff frequency of 1200Hz, 6 dB per octave. I know how to use Butterworth filter.vi, but don´t know how to implement my specifications. I don´t  have Digital Filter Design toolkit. Can it be done without this toolkit?

I checked help and examples finder, but it didn´t give me any clue.

I have LabVIEW 2013

[johnsold · Accepted solution]

6 dB per octave multiplied by the number of poles or the order of the filter is the rolloff of a Butterworth filter. So you need a 1st order filter.

Use the Butterworth Filter.vi from the Signal Processing >> Filters palette. Set the order to 1. Set the type to Highpass.  Set low cutoff freq: fl to 1200 Hz.  Note that you set the low cuttof frequency, not the high frequency cutoff as you might expect. Read the detailed help for the confusing details.

Lynn

[TomTomTomTomTom]

Thanks!!!

As I understand -> 6 dB/octave is default value for first order Butterworth filter?

[johnsold]

Yes, you get 6 dB/octave rolloff per pole (or per order) for a Butterworth filter. So a 4th order filter would have a 24 dB/octave rolloff.

Lynn