3 ms·

Huh. It didn't really answer the question for me, but, anyway, now I'm more wondering about how comes that this question never occured to me in my entire life.

by krick 4y ago

Huh. It didn't really answer the question for me, but, anyway, now I'm more wondering about how comes that this question never occured to me in my entire life. This seems like the most obvious thing to ask, but I don't remember ever wondering about it.

bl0rg 4y ago
Same. I love that feeling.
yetihehe 4y ago
Short answer: It gets pushed out in other places. Long answer: When you try to do destructive interference, you do it only in specific places, you have valleys and peaks somewhere else. Energy from valleys (detructive interference) just enlarges peaks and makes them brighter. As first commenter on that topic said, you can't make destructive interference without making constructive one in different place, so energy is not lost.
dennis-tra 4y ago
Same here! I once came across a similar question that asked where energy goes when light red-shifts from distant galaxies.
dvh 4y ago
At uni professor was drawing inverse FFT of impulse response in a filter and he only used first few frequencies and then asked "can anybody see what's wrong with this chart?". We were all silent... Turns out if you only use first few frequencies of FFT the filter output will look like it respond slightly before the signal arrives. It's a freaking time machine.
- jononor 4y ago
  Non-causal filters can be quite useful, and can be realized when the entire input sequence is available. And if one puts in a delay line, then can work without needing access to future timesteps. A bit harder to realize with electronics or mechanics than software though...
- xnoreq 4y ago
  What are you talking about? Do you mean first few frequency bins, and setting the others to zero? That would be a simple linear-phase lowpass filter. And if you do the shifting properly then you will see that it has a positive group delay. There are filters with negative group delay, however. But FFT is irrelevant for that and it's not a time machine either.

by krick 4y ago

bl0rg 4y ago

Same. I love that feeling.

yetihehe 4y ago

Short answer: It gets pushed out in other places. Long answer: When you try to do destructive interference, you do it only in specific places, you have valleys and peaks somewhere else. Energy from valleys (detructive interference) just enlarges peaks and makes them brighter. As first commenter on that topic said, you can't make destructive interference without making constructive one in different place, so energy is not lost.

dennis-tra 4y ago

Same here! I once came across a similar question that asked where energy goes when light red-shifts from distant galaxies.

dvh 4y ago

At uni professor was drawing inverse FFT of impulse response in a filter and he only used first few frequencies and then asked "can anybody see what's wrong with this chart?". We were all silent... Turns out if you only use first few frequencies of FFT the filter output will look like it respond slightly before the signal arrives. It's a freaking time machine.

jononor 4y ago
Non-causal filters can be quite useful, and can be realized when the entire input sequence is available. And if one puts in a delay line, then can work without needing access to future timesteps. A bit harder to realize with electronics or mechanics than software though...
xnoreq 4y ago
What are you talking about? Do you mean first few frequency bins, and setting the others to zero? That would be a simple linear-phase lowpass filter. And if you do the shifting properly then you will see that it has a positive group delay. There are filters with negative group delay, however. But FFT is irrelevant for that and it's not a time machine either.