Negative Frequency, Imaginary Numbers and the Complex Conjugate

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
www.amazon.com/dp/B0B1BY5H6T
You can preview the first few chapters of the book by signing up for the email list at:
eepurl.com/hko0dT
Playlist: Understand the output of the FFT
• Understand the output ...
Image of Sound Level Meter used in Thumbnail by Jin Zan:
commons.wikimedia.org/wiki/Fi...
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

Пікірлер: 50

  • @karthikeyanm9339
    @karthikeyanm93393 ай бұрын

    This is excellent! I have always wondered about negative frequency but never was able to understand. You explained it so beautifully! Also decomposing the signal into cosine and since components made me realise these concepts more clearly for the first time, I never even thought this decomposition existed!!! Everything is so intuitively explained, you are a fantastic teacher ❤

  • @quaternion-pi
    @quaternion-pi Жыл бұрын

    Your book clearly explains these concepts that have always puzzled me. Thanks.

  • @MarkNewmanEducation

    @MarkNewmanEducation

    Жыл бұрын

    Thank you. It makes me SO happy to hear it. These are things that always puzzled me too. The book is a result of my own journey to understanding the Fourier Series.

  • @vmmehta

    @vmmehta

    Жыл бұрын

    @@MarkNewmanEducation can you pls tell me which book have you published

  • @EpsilonZRho
    @EpsilonZRho Жыл бұрын

    Mark, I want to thank you for the effort and production quality you put into your videos - your animations are top-notch. While they haven't transformed me into an overnight mathematician superstar, they have significantly aided in giving me intuition about a topic I knew practically nothing of. Personally, I now consider you to be among the top youtube educational channels, which places you among esteemed company. I hope for everyone's sake that you keep making these high-quality videos, and that whatever reward you gain from it makes it worth your while. I just purchased your book in part to support your efforts, with its reasonable price being another thing I want to commend you for. Keep up the great work!

  • @MarkNewmanEducation

    @MarkNewmanEducation

    Жыл бұрын

    Thank you for your kind words. I LOVE making these videos as I found these concepts so hard to understand when I was a student and I get a real kick when people write back to me saying that I have helped them understand things I always found so difficult. I'm currently looking around for funding so I can spend my days just making videos. In the meantime, my second book: "How the Fourier Transform Works" is on the way. I'm busy writing it as we speak.

  • @EpsilonZRho

    @EpsilonZRho

    Жыл бұрын

    @@MarkNewmanEducation I'm looking forwards to your new book! You are a top-notch educator!

  • @dosgos
    @dosgos Жыл бұрын

    Perfect timing Mark! I was just studying the interesting concept of negative frequencies. Keep up the fantastic videos.

  • @MarkNewmanEducation

    @MarkNewmanEducation

    Жыл бұрын

    Oh, that's amazing! The concept of negative frequency baffled me for years and no-one seemed to worry why all the FT spectra were drawing with negative frequency. I'm happy to finally plug that knowledge gap. Really glad to have helped. Please share with anyone who you feel it might help. I'm already hard at work on the next video.

  • @JohnyMad1988
    @JohnyMad1988 Жыл бұрын

    Saw two videos. Immediatly bkught the book. Freat explanations, to the point od the practitioner. I was rustt after some years and theae videos helped a lot.

  • @MarkNewmanEducation

    @MarkNewmanEducation

    Жыл бұрын

    Amazing. Really glad the videos were useful to you. There is a second book out now too which continues from where the first book ended. Here is a link to the series on Amazon: www.amazon.com/dp/B0BSJJ69Z1?binding=paperback&ref=dbs_dp_rwt_sb_pc_tpbk

  • @aaron6807
    @aaron6807 Жыл бұрын

    Sir, thank you so much. Your videos are great for giving intuition of complicated subjects

  • @eshabyalcn2747
    @eshabyalcn2747 Жыл бұрын

    Hi Mark, firstly thank you so much for excellent explanation. I just don't understand one thing. In your previous videos which about of Fourier Transform, you say "complex number result of Fourier Transform is contains either phase and amplitude information". The amplitude of real and imaginary component's of Fourier transform result also cover the phase information. During the performing Inverse Fourier Transform, we added negative frequency and positive frequency sinusoids as a result imaginary components are cancelled each other. In this situation, the magnitude of reconstructed sinusoid or real component of the reconstructed signal is 2 times bigger than real component of negative and positive frequency's ( actually this is eliminated by 1/2 which is out of integral). However, the imaginary part is 0. This situation, we get a real cosine wave and 0 phase degree. This is absolutely unacceptable because one properity of wave is dissapered. Please if I'm wrong you say this and explain me that mechanism.

  • @georgethomas8138
    @georgethomas8138 Жыл бұрын

    Excellent! gave me insight and understanding I didn't have

  • @MarkNewmanEducation

    @MarkNewmanEducation

    Жыл бұрын

    Really happy to have helped. Please share so I can help others too.

  • @bertronixtv
    @bertronixtv Жыл бұрын

    Thank you. You really made the abstracted concept a really chewable one. Awesome!

  • @MarkNewmanEducation

    @MarkNewmanEducation

    Жыл бұрын

    Amazing. It's nice to know that I have achieved what I set out to do. As Einstien once said: “Most of the fundamental ideas of science are essentially simple, and may, as a rule, be expressed in a language comprehensible to everyone.” Our job as teachers is to find that language.

  • @bertronixtv

    @bertronixtv

    Жыл бұрын

    @@MarkNewmanEducation Thanks for sharing. You are awesome. More to come 👍.

  • @bjrcomputacion
    @bjrcomputacion Жыл бұрын

    I absolutely loved the explanation of the "real life" implications of negative frequencies, I work with audio synthesis and see those sidebands all the time, but I never thought of them as related to this concept and even to the spacing between radio signal bands, It seems so natural now. Thank you!

  • @MarkNewmanEducation

    @MarkNewmanEducation

    Жыл бұрын

    You're most welcome. I learned about single-side-band modulation years ago, but never understood it, or why it happened. The same is true of imaginary numbers. Only when I began working with these concepts professionally did the two come together for me in a practical way.

  • @ec11368
    @ec11368 Жыл бұрын

    Thank you very much, Mark. You have corrected many misconceptions about the Fourier transformation. I understood many things confusing me about the Fourier transformation for more than six years. Many thanks.

  • @MarkNewmanEducation

    @MarkNewmanEducation

    Жыл бұрын

    Really glad to have helped. Please share and help me help more people.

  • @Jedlmind
    @Jedlmind7 ай бұрын

    I cannot thank you enough.

  • @danielbeirao6071
    @danielbeirao6071 Жыл бұрын

    Congratulations! Well explained!

  • @MarkNewmanEducation

    @MarkNewmanEducation

    Жыл бұрын

    Thank you. I've always found these concepts really difficult to understand. These videos are the result of how I finally understood it myself.

  • @Albert_C
    @Albert_C Жыл бұрын

    Why does the baseband frequency of your voice contain negative frequency? Or is that the FFT results of the time domain voice signal?

  • @MarkNewmanEducation

    @MarkNewmanEducation

    Жыл бұрын

    That's the really weird thing. This negative frequency is a physical phenomenon. I have no way, beyond the ideas I expressed in the video, to intuitively explain why it is so. It just is! This may suggest that imaginary numbers are not so imaginary after all; that they too are a physical phenomenon. It's not just an artifact of the FFT. Certainly in physics they are now beginning to think that the imaginary dimension, as Decartes called it, is a real thing, not just a trick of the maths. Mind blowing, I know.

  • @voidisyinyangvoidisyinyang885
    @voidisyinyangvoidisyinyang8856 ай бұрын

    can you make a video on noncommutative phase of negative frequency as nonlocality? thanks

  • @petrparizek9945
    @petrparizek994510 ай бұрын

    Let me add something to this. There's that thing called the Hartley transform. For a start, the Hartley kernel is neither a sine wave nor a cosine wave. It's phase-shifted exactly midway between these two. Now you might wonder: "What the hell does he need this strange phase shift for?" Well, if you play this thing backwards, what happens? Surprise surprise, it's the same as if you start a quarter-period ahead. This means that you can get any possible phase shift just by changing the ratio of the two amplitudes (i.e. the one of the positive-frequency Hartley sinusoid compared to that of the negative-frequency Hartley sinusoid). Which in turn tells me that this way, I can represent any possible signal that I could ever think of, with the added advantage that I don't need complex numbers this time. By which I mean, there's even a 1-dimensional way of representing negative frequencies and this representation still has its use and its meaning. Without negative frequencies, my signals would be similarly limited as if I sticked just to sine waves without cosine waves or vice versa.

  • @MarkNewmanEducation

    @MarkNewmanEducation

    10 ай бұрын

    Fascinating! Thanks so much. I must research this further.

  • @amoghnelavigi

    @amoghnelavigi

    7 ай бұрын

    Hi, can you give me some links or any sources, where I can understand this concept of negative frequency in more depth. Even after watching the video, I still have a lot of questions regarding its physical interpretations, real world applications etc. Can we generate signals with negative frequencies with an oscilloscope?

  • @petrparizek9945

    @petrparizek9945

    7 ай бұрын

    @@amoghnelavigi It's the same thing as reversing the thing in question. If your periodic waveform has a frequency of 100 Hz and you play it backwards, then the frequency of your reversed signal is -100 Hz.

  • @ZenoDiac
    @ZenoDiac Жыл бұрын

    Wow, new video!

  • @deroberallmann9844
    @deroberallmann9844 Жыл бұрын

    Very good Video Mark ! Could you also make such a grate one on Discrete Cosine Transforms? Kind Regards

  • @MarkNewmanEducation

    @MarkNewmanEducation

    Жыл бұрын

    Thanks for the idea. I've added it to my list of future videos. However, I need to understand the DCT myself first. Will research it.

  • @longluo1788
    @longluo1788 Жыл бұрын

    Could you make a video explain the details of 2D Fourier transform? I am a bit confused about the MRI about the phase and sptial frequency. Thank you mark.

  • @MarkNewmanEducation

    @MarkNewmanEducation

    Жыл бұрын

    You are not the first to ask for this interestingly. This is something I will have to research. Thanks for the suggestion.

  • @JohnyMad1988
    @JohnyMad1988 Жыл бұрын

    God bless you

  • @caca-bt8et
    @caca-bt8et Жыл бұрын

    Dear Newman, initially thanks for your amazing videos you are a great instructor. I have a question to you why don't you upload these videos on Udemy. You can access more people with it.

  • @MarkNewmanEducation

    @MarkNewmanEducation

    Жыл бұрын

    Thank you for your kind words and suggestion. Udemy is indeed one of the directions I am considering. However, I need enough material for a whole course. I feel I am not quite there yet. I have many ideas though waiting to be turned into videos.

  • @yosoylibre
    @yosoylibre Жыл бұрын

    Excelent!

  • @MarkNewmanEducation

    @MarkNewmanEducation

    Жыл бұрын

    Thank you.

  • @bayestraat
    @bayestraat Жыл бұрын

    Could you explain what is a Hamming window and why is it applied with FFT?

  • @MarkNewmanEducation

    @MarkNewmanEducation

    Жыл бұрын

    kzread.infoxoE2rnwFROs

  • @vmmehta
    @vmmehta Жыл бұрын

    Can you please make an intuitive video on Reciprocal Space as a Fourier Transform of Real Space ?

  • @MarkNewmanEducation

    @MarkNewmanEducation

    Жыл бұрын

    Ooooh. I'd have to research that. Thanks for the idea. I've added it to the list.

  • @gadxxxx
    @gadxxxx Жыл бұрын

    It seems impossible ro buy your book at the moment. Amazon says it's unavailable. They only have a Kindle edition. I don't use Kindle. Any news on when it will be available in paperback.

  • @MarkNewmanEducation

    @MarkNewmanEducation

    Жыл бұрын

    Where are you located? It is already available in paperback, but due to the Amazon print on demand limitations, they only have the paperback available in certain countries. However, it should be possible to order in from a different Amazon store that does support the print on demand service.

  • @gadxxxx

    @gadxxxx

    Жыл бұрын

    @@MarkNewmanEducation I;m in Melbourne Australia. I've checked Amazon Australia and Amazon U.S. No luck there. Do you know of one where It's available? I don't know the price so I don't know if I can afford to buy it. 🙂

  • @abdeljalilpr2033
    @abdeljalilpr2033 Жыл бұрын

    Please watch Othman ibn Farouk's videos