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Thread: Finding the fourier transform of a non periodic signal

  1. #1

    Finding the fourier transform of a non periodic signal

    Hello,

    I did an experiment where an app on my phone recorded the frequency of my car's horn. I did it in two situations (Note: I opened the bumper of the car and recorded right above it):

    1. Horn while engine and air conditioner are turned off
    2. Horn while engine and air conditioner are turned on.

    I've attached pictures with the data that I recorded with a graph for both experiments. So my goal here is to try and find the Fourier Transform of both of those graphs. Here is where the difficult part (for me) is. I'm not perfect with this topic and suck at coding. I know that the formula requires you to have a function of time, but since this is a non-periodic signal, I have no clue how to do it. I'm sure that there are simulations out there that can do it for me, but I find it more interesting to do it manually. However if there is no way to do it manually, please recommend a simulation.


    Also, I'm in my final year of the IB Programme (I'm 15), so please try to make your explanations sound as simple as possible. If you don't want to, then its fine by me: more opportunities to learn new things.

    FT Engine+horn.JPGFT Horn.JPG

  2. #2
    Elite Member
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    1) Look up "Fast Fourier Transform". You will need to sample your data and get the right number of points.
    2) If your data are finite, then they are periodic.
    3) Why do you think there is a "simple explanation"? If you don't know what you are doing, no explanation will suffice.
    "Unique Answers Don't Care How You Find Them." - Many may have said it, but I hear it most from me.

  3. #3
    Elite Member stapel's Avatar
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    Cool

    Quote Originally Posted by Calculus=Luv View Post
    ...my goal here is to try [to] find the Fourier Transform of both of those graphs...

    ...please try to make your explanations sound as simple as possible.
    Unfortunately, it is not reasonably feasible to attempt here to provide the weeks or months (or years) of classroom instruction required to go from freshman- or sophmore-year high-school studies to this topic. However, if you'd like to try some simple-ish self-study, there are many online resources. This one says that you should ignore the mathematical underpinnings and just try to figure out how to use the Transform. This one is an "All About Circuits" overview of FFTs. And this "interactive" guide is described by the author as being the most difficult article he'd ever written (at least to that point), saying that it involves "deep math" and that it's "easy to get lost in the details" (and that's without even considering the various different types of FFT).

    Have fun!

  4. #4
    Quote Originally Posted by tkhunny View Post
    1) Look up "Fast Fourier Transform". You will need to sample your data and get the right number of points.
    2) If your data are finite, then they are periodic.
    3) Why do you think there is a "simple explanation"? If you don't know what you are doing, no explanation will suffice.

    1) Thanks
    2) Didn't know that, thanks
    3) I meant don't use terms like convolution.

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