Sine wave to a straight line

How can I filter a sine wave to make a smooth straight line?

Answer 1

[Star Strider]

Easiest way:

y = mean(x)*ones(size(x));

Otherwise, use a bandstop or notch filter at the frequency of the sine wave.

[mikmen]

Can you please elaborate? Also how do I set up the Matlab code for the notch filter? I am new to this. Thanks again!

[Image Analyst]

A straight line has the same y value for all x values. What y value do you want? How about the mean of your signal? Sounds reasonable, and that is what Star gave you. If you want some other value like the min, or max, or 42 or any other number then just replace mean(x) with your desired number.

[Star Strider]

I outlined the steps in filter design a couple days ago in How to design a lowpass filter for ocean wave data in Matlab?.

Replace the appropriate references to 'lowpass' with 'bandstop' as ‘ftype’ in the butter function (or related functions if you choose another filter design), remembering that for a bandstop filter you will need to specify two frequencies — lower and upper — for the stopband.