Timeline for How does the DFT “identify” phase (and why does `fftshift()` help?)
Current License: CC BY-SA 4.0
8 events
| when toggle format | what | by | license | comment | |
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| Feb 19 at 0:13 | comment | added | Dan Boschen | @empty-inch I am on board it you mean exponential not a real sinusoid, otherwise there are two basis functions to compare to and they can interact | |
| Feb 18 at 23:35 | comment | added | robert bristow-johnson | "the fftshift() circular shift has a favorable effect." It's a corrective effect. It corrects the phase flipping by 180° every adjacent bin. That's because bin 0 of the input and output of the FFT is where t=0 is, not the center bin in the middle of the data. And this answer shows exactly how the complex argument of the Fourier Transform values show exactly the phase angle of the sinusoid, assuming that cosine has 0° phase. | |
| Feb 18 at 22:25 | comment | added | empty-inch | @dan Totally agree! But as far as I can tell, I'm not thinking about phase as a time delay between two sinusoids. I can see why you'd think that, but I'm talking about phase difference because it's precisely the difference I'm interested in - the difference in (instantaneous) phase of a sinusoidal input signal and in a basis exponential of the nearest frequency bin, and the inevitable fluctuation of this difference when the input frequency does not align with the bin. I used the real part of the basis function here in plots for ready 2D visualization of this fluctuation. | |
| Feb 18 at 22:24 | comment | added | empty-inch | @robert I thought your answers very effectively demonstrated situations where the fftshift() circular shift has a favorable effect. But there are also "why" and "how" questions I have, such as this one. I do not believe this has been addressed in another answer, but would be more than happy to be proven wrong! | |
| Feb 17 at 4:39 | comment | added | robert bristow-johnson | empty, you keep asking the same question even after it's been answered for you. | |
| Feb 17 at 3:12 | answer | added | Ash | timeline score: 4 | |
| Feb 16 at 2:30 | comment | added | Dan Boschen | When talking about "phase" with signal processing, I actually find it MUCH easier to throw away the notion that phase is the time delay between two sinusoids. What is actually consistent is that phase is a rotation on the complex plane. And then with that, throw away using sinusoids to explain the basic concepts and go right to the spinning phasor: $e^{j\omega t}$-- ultimately that makes so much more sense. I make that point in this video starting at 13:26. Once you really grasp that, I believe it will answer your fundamental question here. youtube.com/watch?v=RxQWk1PjJLQ&t=792s | |
| Feb 16 at 0:37 | history | asked | empty-inch | CC BY-SA 4.0 |