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Negative Frequency, Imaginary Numbers and the Complex Conjugate

Mark Newman 15,712 3 years ago
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What is negative frequency? Why do we need it? What have imaginary numbers got to do with it? Is it a physical phenomenon or just a quirk of the maths? In this video, we look at what makes a signal real and why negative frequencies make them so. We also look at the role the Inverse Fourier Transform plays in the process, and I demonstrate a physical effect of negative frequency in the real world, just in case you thought that negative frequency was only a quirk of the maths. Book: How the Fourier Series Works https://www.amazon.com/dp/B0B1BY5H6T You can preview the first few chapters of the book by signing up for the email list at: http://eepurl.com/hko0dT Playlist: Understand the output of the FFT https://www.youtube.com/playlist?list=PLWMUMyAolbNv9c9qMoksBWv_YDn57EJHz Image of Sound Level Meter used in Thumbnail by Jin Zan: https://commons.wikimedia.org/wiki/File:Sound_level_meter,_DVM85.jpg Licensed under the Creative Commons Attribution-Share Alike 4.0 International license This image has been modified from its original form 0:00 - Introduction 1:08 - Ident 1:12 - What is a real signal? 2:12 - The Fourier Transform 3:36 - A way to understand what negative frequency is 5:11 - Why the sine component is reversed 6:22 - The frequency domain and complex numbers 7:04 - The Fourier Cube and the Inverse Fourier Transform 10:22 - Negative frequency and the complex conjugate 11:27 - A real-world example of the effects of negative frequency 14:46 - Review and conclusion 15:37 - End Screen

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