very informative and eye opener for amatuers in this field and even for those who are just mugging up things whithout even caring to know what the thing is doing....
thanks a lot for this video ,.....
hope to expect more of such videos in future from u.........
Thank you!! I m a medical imaging student so i didnt need the mathematics behind this crap but i needed a theoretical understanding of this crap. I am not excited to learn this piece of shit but Your lecture has managed to give me an idea how to answer my lab questions and possibly have a bit of understanding for my coming exam. Thank you again!! And I hate this shit
I have seen fourier transformation in the university but I never understood the idea behind of it until watching this video. Such an amazing and clear lecture. Thank you for your help.
I think if you try to think of a physical analogy for a complex number you get confused. A complex number is a mathematical tool that is needed to solve a large class of algebraic equations such as x^2 = -1.
The way I think about it is that there is energy in a sinusoidal wave. Where is that energy at the exact moment(s) the wave amplitude passes through zero? If you represent a wave as having complex amplitude the magnitude is always constant, sometimes the energy is in "imaginary space".
I am afraid I don't have any videos on those topics. I am not a signal processing person and most of my videos are on photonics and optics. I am trying to get a series on electromagnetics together, but it is going more slowly than I would like.
1) You only measure the real part. In the complex eq. A and B themselves are complex which allows you to change the phase of the wave.
2) Orthogonal functions form a set from which any other function can be built. The most common example are the unit vectors, xhat, yhat, and zhat, from which any point in space can be represented. They are orthogonal because changing xhat doesn't affect yhat for example. Move in x, y does not change.
@kridnix Hello Sir, Thank you very much for this video, it helped me lot thank you very much. Sir i have a request that can you give me the link of video tutorials on Short Term FT and WT of yours if any, or any other good video tutorial of your knowledge for the above. I will be very grateful to you. Thanks again for this video. Waiting for reply.
@kridnix Thank you sir! Thanks so much for your answers.
Answers to no. 2 and 3 are crystal clear now. But I still find it difficult to understand answer to question no 1. I see that in your example, the f(t) wasn't complex function--there was a simple addition of cos and sin.
There wasn't any imaginary term. I have two more questions. They are following in next post
4. Practically f(t) is so messy unlike in the example taken by you. If I want to do a fourier transform the way you have done, what should I replace f(t) with in such a case?
For a simple functions, f(t) can be sin8t or cos6t or summation of them, how about complex (I mean messy, not mathematical complex) function. I don't know what f(t) is made of. I don't know different values of w (omega)?
4. Practically f(t) is so messy unlike in the example taken by you. If I want to do a fourier transform the way you have done, what should I replace f(t) with in such a case?
For a simple functions, f(t) can be sin8t or cos6t or summation of them, how about complex (I mean messy, not mathematical complex) function. I don't know what f(t) is made of. I don't know different values of w (omega)?
5. My imagination go haywire whenever I see an imaginary no. What is a complex no.? Can I say that complex no. is a way to represent two orthogonal signals i.e. to say the real part is always orthogonal to imaginary part?
i do not understand why a time signal is represented by a complex form. what will happen if we simply add cos & sin i.e. Acoswt+Bsinwt instead of Acoswt+jBsinwt?
They say sin and cos are orthogonal. Can you briefly give an intuitive idea about orthogonal functions?
Also, fourier transform definition says that any aperiodic signal can be obtained by summing infinite no. of sinosoidal waves. But why is that the data I receive from customer has limited no. of freq in freq domain?
@78uttam For the third question, they are using a numerical Fourier transform and the frequency spacing will be inversely proportional to the sampling rate and proportional to the duration they measured the data for. You can't have an infinite number of frequencies in a time limited window.
I have an issue with your use of Euler's at 3:17 in the vid. Unless I misunderstand, you are suggesting that A and B (the coefficients of cos and sin on rhs) may not be equal. However, e^{jt}=cos(t)+j sin(t), which means that Me^{jwt}=M cos(wt) + j M sin(wt). A and B must equal M (A=B=M). No?
man this was awesome bro, you rock ! i can take the lecture at my pace and pause it when my head hurts... "im not going into a mathematical derivation" THANK YOU ! i was interested in understanding the "why and how the transformation actually works" :D you're transforming education :) Plato would be proud
Eric- Your comment isn't showing up it seems, but to answer your question, if the signal went on to infinity, then there could be infinite energy in it, and you wouldn't expect the series to converge. Most signals are in a limited time range.
Nope, you are right. This was just a mistake in the video where I am confusing the rectangular form A-iB with the polar form. I'll correct it next time I redo the video.
I always learnt that it is equal to Mcos (wt)+ JMsin(wt) that is the polar form which can also be written as A + JB in the normal form where M=root(A^2+B^2). Am i missing something?
@MANOJUPADHYAY37 It works the same way. If you follow the same algorithmic approach you get from frequency back to time (changing the integral equation slightly to integrate over frequency instead of time).
@kridnix very good video, but the summation does not mean to add all the points!! it simply means the value of the signal at particular point in time, the summation is just a convinent way to represent signal at particular time!!!
the delta function is multiplied by f(t), so basically the delta function describes a straight line at each point in time, and the f(t) imposes an amplitude on the delta function corrrect or no?
I don't just play a professor on YouTube, I actually teach electrical engineering at Oklahoma State University. I did these videos so I don't have to lecture in class anymore. It bored the students more than it bored me. Now we build things instead. Much more fun and my students can watch the videos at home.
@kridnix Cool video, we need more of those. You should check the sign in your exponential in the definition. I think it's exp(-jwt) not exp(jwt). Also in the definition, I think you wanted to write "exp(-jwt).dt" and not "exp(-jwt)delta(t)". The delta sign is used in another context of differentiation as you know. ("partial" and "spacial" as keywords).
finally a video that explains fourier series intuitively... gosh i am sick and tired of watching videos that just contain definition, formula and examples. kudos to you - make more videos like this!! good job
I just don't understand ....If you are willing to put time and effort to make a serial video explaining some important physical concept why not get a decent enough microphone to record the voice? perhaps 10 dollars more would do the trick?
Quick question, in your example in the time domain you have AnCos(Wnt) + jBnSin(Wnt) = An[(1/2)(e^jWnt + e^-jWnt)] + (Bn/2)(e^jWnt - e^-jWnt), wouldn't you then have 2 impulses in the frequency domain, one at Wn with amplitude of (An+Bn)/2, and one at -Wn with amplitude of (An-Bn)/2 ? I couldn't get why your frequency domain had so many different frequencies at so many different amplitudes.
Sorry if it's a silly question, I'm just learning this stuff at uni
Yeah, there should be a similar response at negative frequencies, but I didn't include it since it would have made the images smaller and the explanation more difficult. Most people ignore the negative frequencies since they are just a mirror image of the positive.
The reason I had a lot of frequencies was to demonstrate the overlap of the e^(iwt) term of the integral with the multiple frequencies in the signal f(t). I thought having several frequencies might show the point a little better.
@netmazter I have a Motion tablet PC running WIndows XP tablet. I use Powerpoint 2003, and it comes with the ink built in for presentation mode. I use Camtasia Studio for the video capture.
so you essentially saying that in the time domain we vary t to get the plot for each omega..so we need many plots of omega to completely represent the function...
in frequency domain we vary omega and plot for a particular t...so we need many plots of t to get the complete funtion...
@knighttango Sort of... Basically we do create a plot in t, but then we integrate that plot to get a single complex number for a given omega. Then we go to the next omega and integrate that t plot and so on. At the end of this we end up with one plot of the complex amplitude as a function of omega that was obtained by doing integrals of lots and lots of plots as a function of t.
@kridnix How do you get the single number for a particular omega? The integration for that omega in a sinusoid from neg inf to pos inf don't converge.
@kridnix correction sir. only for electrical engineers it is j. for the rest of us, it is i - the great i. i don't understand instead of i, why can't you guys use something else, like c, or something, for current. then yo could also have used i for the imaginary symbol.
Yes, but "j" is also used because Fourier Transforms is widely used in Electrical Engineering, and the "i" can be mistaken for electrical current, not the complex number
man...i have to learn about this shit in my E-Math class.....we just finished Laplace and Eigenvalues......I noticed that my Diff EQ instructed didnt touch on Fourier transforms...nor did he go as far into Laplace trasforms as we did in this course...........man.....I'm sick of school.........Im gonna drop out and start a hotdog stand
Math like BOSS!!! Thanks alot!
BoomBaaamBoom 1 week ago
additive synthesis, a good example of this.
TranceTips 4 weeks ago
Best explanation I found!! Thank you very much!!! =D
JoaoPedroBorlido 1 month ago
buena explicacion.
pluterday 2 months ago
Is this the Cat Yoddeler? You sound like Paul the Cat Wrangler...are you he?
Nexus2Eden 2 months ago
tq very much bro.i'm a student interested for this particular topic
12345soa 2 months ago
I am VERY CONFUSED as to how the "Imaginary " sine wave is related to something real in the real world.
MatrixOfDynamism 2 months ago
excellent video....
very informative and eye opener for amatuers in this field and even for those who are just mugging up things whithout even caring to know what the thing is doing....
thanks a lot for this video ,.....
hope to expect more of such videos in future from u.........
surprizerrr 2 months ago
This has been flagged as spam show
Thank you!! I m a medical imaging student so i didnt need the mathematics behind this crap but i needed a theoretical understanding of this crap. I am not excited to learn this piece of shit but Your lecture has managed to give me an idea how to answer my lab questions and possibly have a bit of understanding for my coming exam. Thank you again!! And I hate this shit
MILSWANCAs 4 months ago
I have seen fourier transformation in the university but I never understood the idea behind of it until watching this video. Such an amazing and clear lecture. Thank you for your help.
SoajanII 5 months ago
thank you very much, I am enlightened...Tusen Takk....!
TheSatyam182 5 months ago
I think if you try to think of a physical analogy for a complex number you get confused. A complex number is a mathematical tool that is needed to solve a large class of algebraic equations such as x^2 = -1.
The way I think about it is that there is energy in a sinusoidal wave. Where is that energy at the exact moment(s) the wave amplitude passes through zero? If you represent a wave as having complex amplitude the magnitude is always constant, sometimes the energy is in "imaginary space".
kridnix 6 months ago
I am afraid I don't have any videos on those topics. I am not a signal processing person and most of my videos are on photonics and optics. I am trying to get a series on electromagnetics together, but it is going more slowly than I would like.
kridnix 6 months ago
O.k. There are three questions
1) You only measure the real part. In the complex eq. A and B themselves are complex which allows you to change the phase of the wave.
2) Orthogonal functions form a set from which any other function can be built. The most common example are the unit vectors, xhat, yhat, and zhat, from which any point in space can be represented. They are orthogonal because changing xhat doesn't affect yhat for example. Move in x, y does not change.
kridnix 6 months ago
@kridnix Hello Sir, Thank you very much for this video, it helped me lot thank you very much. Sir i have a request that can you give me the link of video tutorials on Short Term FT and WT of yours if any, or any other good video tutorial of your knowledge for the above. I will be very grateful to you. Thanks again for this video. Waiting for reply.
Regards
Tushar
tusharaustin 6 months ago
@kridnix Thank you sir! Thanks so much for your answers.
Answers to no. 2 and 3 are crystal clear now. But I still find it difficult to understand answer to question no 1. I see that in your example, the f(t) wasn't complex function--there was a simple addition of cos and sin.
There wasn't any imaginary term. I have two more questions. They are following in next post
78uttam 6 months ago
@kridnix
Two more questions:
4. Practically f(t) is so messy unlike in the example taken by you. If I want to do a fourier transform the way you have done, what should I replace f(t) with in such a case?
For a simple functions, f(t) can be sin8t or cos6t or summation of them, how about complex (I mean messy, not mathematical complex) function. I don't know what f(t) is made of. I don't know different values of w (omega)?
78uttam 6 months ago
This has been flagged as spam show
@kridnix
Two more questions:
4. Practically f(t) is so messy unlike in the example taken by you. If I want to do a fourier transform the way you have done, what should I replace f(t) with in such a case?
For a simple functions, f(t) can be sin8t or cos6t or summation of them, how about complex (I mean messy, not mathematical complex) function. I don't know what f(t) is made of. I don't know different values of w (omega)?
78uttam 6 months ago
@kridnix
5. My imagination go haywire whenever I see an imaginary no. What is a complex no.? Can I say that complex no. is a way to represent two orthogonal signals i.e. to say the real part is always orthogonal to imaginary part?
78uttam 6 months ago
i do not understand why a time signal is represented by a complex form. what will happen if we simply add cos & sin i.e. Acoswt+Bsinwt instead of Acoswt+jBsinwt?
They say sin and cos are orthogonal. Can you briefly give an intuitive idea about orthogonal functions?
Also, fourier transform definition says that any aperiodic signal can be obtained by summing infinite no. of sinosoidal waves. But why is that the data I receive from customer has limited no. of freq in freq domain?
78uttam 6 months ago
@78uttam For the third question, they are using a numerical Fourier transform and the frequency spacing will be inversely proportional to the sampling rate and proportional to the duration they measured the data for. You can't have an infinite number of frequencies in a time limited window.
kridnix 6 months ago
Comment removed
chandraiitk 2 months ago
What is the handwritten drawing program?
lukmackul 8 months ago
I have an issue with your use of Euler's at 3:17 in the vid. Unless I misunderstand, you are suggesting that A and B (the coefficients of cos and sin on rhs) may not be equal. However, e^{jt}=cos(t)+j sin(t), which means that Me^{jwt}=M cos(wt) + j M sin(wt). A and B must equal M (A=B=M). No?
jeffaschwarz 9 months ago
thank you , it's a great video
gcrzg 9 months ago
nice lectures, but you need a better microphone
25380421859 9 months ago
man this was awesome bro, you rock ! i can take the lecture at my pace and pause it when my head hurts... "im not going into a mathematical derivation" THANK YOU ! i was interested in understanding the "why and how the transformation actually works" :D you're transforming education :) Plato would be proud
bubtacular 9 months ago
The "delta function" is called the impulse functions for those of you curious!
ubersuperbatman 9 months ago
THANK YOU for posting these!
TheNaekid 9 months ago
but i do have a problem in understanding the integrals. preparing for my post graduation. but not able to recall the terms
Anushsudha 10 months ago
thanks . understanding is better in this than reading books
Anushsudha 10 months ago
You can do it either way as long as you are consistent. Different books define it different ways.
kridnix 10 months ago
This question might've been asked before but just in case, shouldn't there be a (-) sign in front of jwt for forward fourier transform?
Knightmetal 10 months ago
Eric- Your comment isn't showing up it seems, but to answer your question, if the signal went on to infinity, then there could be infinite energy in it, and you wouldn't expect the series to converge. Most signals are in a limited time range.
kridnix 11 months ago
Awesome video! Thanks a lot! For the first time since the beginning of my course I understand exactly what the FT is about :))
kzawy 11 months ago
Nope, you are right. This was just a mistake in the video where I am confusing the rectangular form A-iB with the polar form. I'll correct it next time I redo the video.
kridnix 11 months ago
How is Me^(jwt)= A cos (wt)+ JBsin(wt)?
I always learnt that it is equal to Mcos (wt)+ JMsin(wt) that is the polar form which can also be written as A + JB in the normal form where M=root(A^2+B^2). Am i missing something?
alifaraj90 11 months ago
@alifaraj90 ---you are correct
TheSujit123 10 months ago
You saved my grade... Thank you!
akeela 1 year ago
@akeela That is what the videos are for!
kridnix 1 year ago
Really good job--intuitive and to the point! thanks!
sbmlinde 1 year ago
Great Explanation
SithBrak 1 year ago
Great Explination
SithBrak 1 year ago
WHAT ABOUT INVERSE FOURIER TRANSFORM?
MANOJUPADHYAY37 1 year ago
@MANOJUPADHYAY37 It works the same way. If you follow the same algorithmic approach you get from frequency back to time (changing the integral equation slightly to integrate over frequency instead of time).
kridnix 1 year ago
@kridnix very good video, but the summation does not mean to add all the points!! it simply means the value of the signal at particular point in time, the summation is just a convinent way to represent signal at particular time!!!
Mrknightrider777 11 months ago
@MANOJUPADHYAY37
LOL CAPS LOCK
MattyHild 1 year ago
mega upload. com/?d=BKXODCMA
ulukulu95 1 year ago
the delta function is multiplied by f(t), so basically the delta function describes a straight line at each point in time, and the f(t) imposes an amplitude on the delta function corrrect or no?
Holyfrik1 1 year ago
Essentially yes. I am not enough of a mathematician to prove absolutely *any* waveform, but as an engineer the approximation is close enough.
kridnix 1 year ago
So any waveform... regardless of how simple or complex can be represented by the summation of sine waves of different amplitude, period and phase?
PapaHeavyPsy 1 year ago
Sinusoidal waves have both amplitude and phase. You need complex numbers to express phase.
kridnix 1 year ago
okay but why is this "j" in front of the sinus? In the fourier-series there is not imaginary term....
IronPump89 1 year ago
Nice explanation! Thanks your work ;)
I'm starting this at uni too :)
RoUbAaRiR 1 year ago
very nice sir i like your way of lecturer very much and kindly share more videos of laplcace transform if u have. thanks alot
sanaullah987 1 year ago
In your first slide, the fourier transform - has a exp-to-pow '-ve', within the integral. Its misleading.
tilak279 1 year ago
Thanks bro, this was helpful.
nkwosman 1 year ago
Thanks for the positive feedback. When I get to teach a new class I'll do a whole new round of videos.
kridnix 1 year ago
I don't just play a professor on YouTube, I actually teach electrical engineering at Oklahoma State University. I did these videos so I don't have to lecture in class anymore. It bored the students more than it bored me. Now we build things instead. Much more fun and my students can watch the videos at home.
kridnix 1 year ago 36
@kridnix I would really like that my university take this approach into teaching. RWTH
max12345678 1 year ago
@kridnix if only every lecturer thinks like you, teaching would be much nicer.. thx
SunSatlON 1 year ago
@kridnix nice..It doesn't help only your students, it helps other students from other universities , like me. Thank you very much.
123damed 4 months ago
@kridnix Cool video, we need more of those. You should check the sign in your exponential in the definition. I think it's exp(-jwt) not exp(jwt). Also in the definition, I think you wanted to write "exp(-jwt).dt" and not "exp(-jwt)delta(t)". The delta sign is used in another context of differentiation as you know. ("partial" and "spacial" as keywords).
Salutations d'Alger.
JugurthaHadjar 2 months ago
thanks! I understand this better after watching your video. You could give my professor a run for his money, ever consider teaching?
jwaffe 1 year ago
finally a video that explains fourier series intuitively... gosh i am sick and tired of watching videos that just contain definition, formula and examples. kudos to you - make more videos like this!! good job
sammyjny 1 year ago
in The fourier transform is it e^(-1)jwt or e^jwt?
Jesus! half the books have it in the first way,half have it in the second?
Why? and which is right?
Imban3z 1 year ago
@Imban3z I guess it wouldn't matter much which one you use. One's just negative. :S
chriswyatt 1 year ago
The quality is making my ears bleed .
I just don't understand ....If you are willing to put time and effort to make a serial video explaining some important physical concept why not get a decent enough microphone to record the voice? perhaps 10 dollars more would do the trick?
Chr0nalis 1 year ago
Hi thanks for the video!
Quick question, in your example in the time domain you have AnCos(Wnt) + jBnSin(Wnt) = An[(1/2)(e^jWnt + e^-jWnt)] + (Bn/2)(e^jWnt - e^-jWnt), wouldn't you then have 2 impulses in the frequency domain, one at Wn with amplitude of (An+Bn)/2, and one at -Wn with amplitude of (An-Bn)/2 ? I couldn't get why your frequency domain had so many different frequencies at so many different amplitudes.
Sorry if it's a silly question, I'm just learning this stuff at uni
frenzaldude 1 year ago
Yeah, there should be a similar response at negative frequencies, but I didn't include it since it would have made the images smaller and the explanation more difficult. Most people ignore the negative frequencies since they are just a mirror image of the positive.
The reason I had a lot of frequencies was to demonstrate the overlap of the e^(iwt) term of the integral with the multiple frequencies in the signal f(t). I thought having several frequencies might show the point a little better.
kridnix 1 year ago
it's so robotic....except for whoo
bestozesto 1 year ago
Very definitive presentation.. could you tell me the tool you used to highlight your slides with a marker...
netmazter 1 year ago
@netmazter I have a Motion tablet PC running WIndows XP tablet. I use Powerpoint 2003, and it comes with the ink built in for presentation mode. I use Camtasia Studio for the video capture.
kridnix 1 year ago
so you essentially saying that in the time domain we vary t to get the plot for each omega..so we need many plots of omega to completely represent the function...
in frequency domain we vary omega and plot for a particular t...so we need many plots of t to get the complete funtion...
knighttango 1 year ago
@knighttango Sort of... Basically we do create a plot in t, but then we integrate that plot to get a single complex number for a given omega. Then we go to the next omega and integrate that t plot and so on. At the end of this we end up with one plot of the complex amplitude as a function of omega that was obtained by doing integrals of lots and lots of plots as a function of t.
kridnix 1 year ago
@kridnix How do you get the single number for a particular omega? The integration for that omega in a sinusoid from neg inf to pos inf don't converge.
ErikWestrup 11 months ago
excellent. Fourier transforms are crystal
bleakleper 1 year ago
10x better than the explanation from my professor at ucla. thanks.
rollerboogie 2 years ago
thanks. one complaint though.... it's i not j.
HulluRusakko 2 years ago
Ah, you must be a physicist or a mathematician, not an engineer. To us engineers it is j.
kridnix 2 years ago
i is for any physicist mathematician or any other engineer, to electrical engineering is j
sajaldi1 2 years ago
@kridnix correction sir. only for electrical engineers it is j. for the rest of us, it is i - the great i. i don't understand instead of i, why can't you guys use something else, like c, or something, for current. then yo could also have used i for the imaginary symbol.
iamanwer 1 year ago
Yes, but "j" is also used because Fourier Transforms is widely used in Electrical Engineering, and the "i" can be mistaken for electrical current, not the complex number
darthsexiest2727 2 years ago
thanks a lot!!! i hope you would be my teacher!!
sorolopas 2 years ago
thx frm TÜRKİYEEEEE
corumspor86 2 years ago
This comment has received too many negative votes show
nobody likes you, you dirty turk.
steveofreeblind 1 year ago
Comment removed
steveofreeblind 1 year ago
great, thanks for posting.
ndjarnag 2 years ago
man...i have to learn about this shit in my E-Math class.....we just finished Laplace and Eigenvalues......I noticed that my Diff EQ instructed didnt touch on Fourier transforms...nor did he go as far into Laplace trasforms as we did in this course...........man.....I'm sick of school.........Im gonna drop out and start a hotdog stand
MrHarris5406 2 years ago 21
^^ just put on some calm music and learn this stuff
IronPump89 2 years ago
Ah sorry, i see you already answered that question.
nikookin1234 2 years ago
Hi, this is a very good video, but i have a question. The first formula, must it not be: ...e^ -(j*omega*t) ... absence of a minus?
nikookin1234 2 years ago
Thanks!!!! English is not my primary language, but i understood everything fine!!!! Very nice!!!
stylefighterdks 2 years ago
Nice explanations! Helped me a lot!! Thanks
TheWye 2 years ago
thank you
ee04395 2 years ago
nice explanation.
By the way,shouldnot the higher frequency components have lower magnitudes while representing a signal as sum of sinusoids?
He shows a third frequency component with higher amplitude than the prvious one.
Nice one though
vasantheee 2 years ago
thanx buddy it helps me very much
pinkunath 2 years ago
thanks very helpful
greetings from germany
DonArkadi 3 years ago
Thanks for the comment. You can define phase either with a positive or negative exponential. Different texts use different conventions.
kridnix 3 years ago
Good explanation. I want to point out a mistake in the F(w) formula. The complex exponential e^(jwt) should be e^(-jwt). Please correct.
shazaduh 3 years ago