FFT basic concepts

Рет қаралды 350,643

11 жыл бұрын

Basic concepts related to the FFT (Fast Fourier Transform) including sampling interval, sampling frequency, bidirectional bandwidth, array indexing, frequency bin width, and Nyquist frequency.

Пікірлер: 70

@SpMeKP 8 жыл бұрын

Short, comprehensive, to the point. Loved it. I've been going through tons of resources around the net the past few days, and I couldn't find what I needed till I stumbled upon this video.

@nurjaman4756 2 жыл бұрын

Hh5 GT6

@Anand-N 10 жыл бұрын

Thank you so much for the video. Best explanation so far I found in the internet

@matiasmdq8569 6 жыл бұрын

I needed to remember the FFT concepts. Your video was a very useful way to do it, so thanks you !!

@CoolestFlame 9 жыл бұрын

Thank you. This gives an overall image on FFT. Great video.

@ronaldgulbrandson7677 8 жыл бұрын

This is one of the best explanations of the FFT results that I have found on the Internet.

@seanbro92 7 жыл бұрын

wrong, this tells nothing about FFT, they're just DFT principles

@ntspress 10 жыл бұрын

The FFT gives you a two-sided spectrum. When you shift the output array elements to place DC (index k=0) in the center you get negative frequencies on the left side and positive frequencies on the right side, and fmax appears at the far right side. The bidirectional bandwidth refers to the *total* spectrum occupied by this two-sided spectrum, and because DC is in the middle, fmax is only half the bidirectional bandwidth.

@abijit.jkurup8231 4 жыл бұрын

Could you explain with an example

@faizanzahid490 4 жыл бұрын

This could only ve understood if you're working on the hardware and have experienced how acquisition of bandwidth is done when tune a radio at a certain center freq.

@changbadinesh 3 жыл бұрын

@NTS. ....If time(t) starts at zero then time instant of last sample minus that of first sample(0) is (N-1)*Td/N ... which is not equal to the time length of signal (Td)....what the heck you guys are talking......It read more than hundred of paper on FFT and DFT , all of them are using this dumb index system (0 to n-1) and that silly mistake though its has no such significant effect it can;t be neglected.... Correction way 1: If you take N samples ..then it has N discrete time instants ...but indeed (N-1) intervals only....that's make size of interval to be Td/(N-1) in fact indeed..... Correction way 2: If you stick at signal length to be Td then...your index should run from 0 to N.....thereby making total number of samples to be (N+1) .....total number of interval to be N.... and one more thing what you described is DFT... not FFT...not at all hehe

@Rosemary137 8 жыл бұрын

Very clear. Thank you so much!!

@saltcheese 5 жыл бұрын

this is exactly what i needed! gracias!

@ademariocarvalho 10 жыл бұрын

Excellent explanation!!!

@davidwang3454 6 жыл бұрын

This is perfect explain on dft. It clear up the basic concept. I am wondering if got similar topic for 2d fft, tks a lot

@mjf1422 10 жыл бұрын

Thank you so much for this video. May Allah give you the best in the life and the next :).

@zizou202 8 жыл бұрын

Thank you so much. brief and clear.

@43SunSon 7 жыл бұрын

Question, why Bb=fs ? Thank you.

@n.aminr.7175 7 жыл бұрын

why the time domain signal time interval, Δt divided by N and not N-1? Since it is the interval. There will be an offset by (100/N)% by the sampling time calculation.

@AnthonyMcEgan 10 жыл бұрын

Great video. Thanks, Anthony

@JeffreyNuccio-gd4gz Жыл бұрын

Excellent video!! thank u

@curiousSloth92 9 жыл бұрын

Very clear ty!

@mohammedalzabidi2137 5 жыл бұрын

Thanks a lot , very helpful

@hemanthkumark9557 7 жыл бұрын

was very usefull, thanks a lot!

@Seff2 3 жыл бұрын

Very usefull for me. I don't care how the FFT is calculated, I just want to know whats the input and whats the output

@sakalaimu 10 жыл бұрын

What is bidirectional bandwidth, why does it equal to sampling frequency, and why does maxima of frequency equal to half of bidirectional bandwidth? Thanks for the video btw.

@rokkuform 7 ай бұрын

exactly what I needed

@MakeUDawn 6 жыл бұрын

It is clear but sadly it tells nothing about the FFT, just some basic definitions of DFT.

@eric_welch 6 жыл бұрын

thank you!! no formulas, no actual plots of time and frequency domains ...a bit disappointed here tbh

@tungvu1214 3 жыл бұрын

Equal about fft is very many on the internet. This video is exactly what i need.

@lostacecaz 10 жыл бұрын

why is the time of the final sample [(N-1)/N]*td? isn't it just td?

@ntspress 10 жыл бұрын

Because the first sample is at time zero its sample index is also zero. For example, suppose you have 8 samples beginning at time zero. The index of the first sample is 0, the next index is 1, and the final sample has index 7. If you started indexing at 1, then the final sample index would be 8.

@anam4101 7 жыл бұрын

Hi, Thanks for the video. I have a doubt what do you mean by "typically display only lower half of the output array". If there are N samples in => N samples out. So did u mean, its N samples in=> N/2 Samples out?

@collinatorstudios3268 7 жыл бұрын

If you go past N/2 in the frequency array, it is actually is just a mirror image of the previous N/2 frequency bins. See this answer: dsp.stackexchange.com/a/4827/11807

@krrishnacreations5551 5 жыл бұрын

good explained fft

@memonafayaz8382 6 жыл бұрын

Good explanation

@TheMechatronicEngineer Жыл бұрын

Brilliant!

@kasunperera763 2 жыл бұрын

Well explained thank you

@abdullahjhatial2614 2 жыл бұрын

how number of input samples is equal to out samples?

@anhta9001 Жыл бұрын

Can someone explain what is the bidirectional bandwidth?

@orangedac 10 жыл бұрын

Thanks a lot

@haya4895 4 жыл бұрын

thanks alot, it is helpful

@rcollins0618 9 жыл бұрын

Thanks!!

@manugupta9940 6 жыл бұрын

After going through so much bullshit over internet and youtube, this is what I wanted.

@richardphillips2405 3 жыл бұрын

I don't understand the concept of bidirectional bandwidth. Shouldn't 0 (DC) be at the left and then the higher frequencies go to the right? I don't understand about or why you put 0 (DC) in the center.

@mohamedmoumou6682 Жыл бұрын

Thank you so much sir

@pks126 5 жыл бұрын

short precise and to the point explanation of FFT ....it transform time domain waveform to frequency domain spectrum ......but why there is a need for FFT please explain

@lwghj1976 4 жыл бұрын

many thanks

@prashantkumarsisodiya221 5 жыл бұрын

thank u so much

@dasgoood2811 2 жыл бұрын

Thank you sooooooooooooooooooooooooo much

@abdelmichel3371 6 жыл бұрын

Am I wrong or Delta_t should be equal to T_d/(N-1)?

@abdelmichel3371 6 жыл бұрын

Because t_i=i*Delta_t so t_N-1=(N-1)*Delta_t=T_d

@oncubenli5461 5 жыл бұрын

Time starts at 0 and runs until N-1 meaning there are N samples for duration T_d. So you got T_d/N as width of time steps or Delta_T. In other words, you would be right if n started from 1 instead of 0.

@brandonrude9955 10 жыл бұрын

This video is very well done. Saving my ass!

@xinpengdu3815 7 жыл бұрын

Thanks a lot for clear explanations on FFT.

@akhil6385 5 жыл бұрын

@dimitrisdaniel 6 жыл бұрын

in 2:39 you say that the sampling interval Dt is Td/N, normally Dt is equal to Td/(N-1) so in the end total time Td=(N-1)*[Td/(N-1)]=Td

@dimitrisdaniel 3 жыл бұрын

Thank you for your reply, even after some years. I also end up to this when I code the algorithm and it turns more convenient to start from zero. Continue your great job.

@rahulsanthosh5034 2 жыл бұрын

how Bb = Fs?

@UnbeknownToHis 6 жыл бұрын

God bless you, sir.

@ahmadfuadi6838 Жыл бұрын

jdyehynshd

@ahmadfuadi6838 Жыл бұрын

jsksj

@sddf2476 3 жыл бұрын

Thanks

@linajerbou9473 2 жыл бұрын

can somone explain this? f(t)=sin(at)+sin(bt)

@BogdanTheGeek 2 жыл бұрын

cool cool cool, but where is the algorithm????

@EVILDASDINGO 6 жыл бұрын

i don't understand monkeyshit, not from this video, not from any other i've watched about the FFT or any explanation i've read on the internet.

@changbadinesh 3 жыл бұрын

@NTS.....If time(t) starts at zero then time instant of last sample minus that of first sample(0) is (N-1)*Td/N ... which is not equal to the time length of signal (Td)....what the heck you guys are talking......It read more than hundred of paper on FFT and DFT , all of them are using this dumb index system (0 to n-1) and that silly mistake though its has no such significant effect it can;t be neglected.... Correction way 1: If you take N samples ..then it has N discrete time instants ...but indeed (N-1) intervals only....that's make size of interval to be Td/(N-1) in fact indeed..... Correction way 2: If you stick at signal length to be Td then...your index should run from 0 to N.....thereby making total number of samples to be (N+1) .....total number of interval to be N