56
votes
How do computers store sound waves just by sampling the amplitude of a wave and not the frequency?
"Amplitude" is the wrong word. The amplitude of a periodic function is the difference between its greatest value and its least value. Cross out "amplitude" from your textbook, and ...
- 15.2k
45
votes
Why are cosine and sine functions used when representing a signal or a wave?
While Sine and Cosine functions were originally defined based on right angle triangles, looking at that point of view in the current scenario isn't really the best thing. You might have been taught to ...
- 3,187
43
votes
How do computers store sound waves just by sampling the amplitude of a wave and not the frequency?
A slight clarification on Solomon Slow's complete answer:
If you sample the original signal frequently enough, the instantaneous values you measure at each of those tiny time slices will actually ...
- 95.5k
35
votes
Accepted
Convolutions in Physics
Preamble
The lesson here is that graphical intuition isn't always the best choice. For example, you can say that the intuition for derivatives is that they're slopes, and for integrals is that they'...
- 103k
30
votes
How do computers store sound waves just by sampling the amplitude of a wave and not the frequency?
Your instinct is correct, there are two degrees of freedom here so we have to measure two quantities. The one you are missing is the timestamp. We are measuring both the voltage of the signal and ...
- 507
28
votes
Why does a capacitor act as a frequency filter?
An capacitor has one intuitive property:
Its voltage can't change instantly since its voltage is dependent on the charge it has stored, and charge doesn't move at infinite speeds (there is always ...
- 9,319
25
votes
Can we quantify the pitch of a sound that is a mixture of many frequencies?
Pitch can be described as a subjective perception of an auditory stimulus which cannot be objectively, unambiguously quantified. It is strongly related to the objective physical property of frequency ...
- 9,920
25
votes
Feynman claimed "The ear is not very sensitive to the relative phases of the harmonics." Is that true?
What Feynman means by that statement is that the "ear" (cochlea) is a spectrum analyzer with a large set of very narrow band filters each followed by a square law (energy) detector, that is ...
- 19.8k
24
votes
Can sound waves be modulated?
Can you modulate sound waves?
Of course. In fact, back in my day, if we wanted to connect to a remote computer, we had to modulate our sound waves and then send them through the telephone.
https://en....
- 15.2k
17
votes
Can sound waves be modulated?
What you can do for electromagnetic waves, eg amplitude modulation, frequency modulation, etc, you can do for sound waves. The problem with sound waves for communication is that they tend to be ...
- 97.9k
16
votes
Avoiding radar detection using active noise control instead of a stealth fuselage
To get an idea of the difficulties, we will consider a similar problem with sound. There are places with names like "Echo canyon". If you shout, the sound reflects of a nearby canyon wall ...
- 41.1k
14
votes
Fourier vs. Laplace transforms
Fourier and Laplace transforms are so closely related that the substitution $s \Leftrightarrow i \omega$ usually works in practical cases to turn one into the other (may need to adjust normalization). ...
- 21.8k
14
votes
Avoiding radar detection using active noise control instead of a stealth fuselage
The essential problem with that is that transmitting emits energy. You can cancel out the reflection in a particular direction this way, but in other directions it won't cancel. In effect, you're ...
- 21.8k
14
votes
What does "DC" mean in gravitational physics?
What does "DC" mean...
"DC" means "Direct Current." It is often used in contrast to "AC," which means "Alternating Current."
Alternating current ...
- 21.9k
13
votes
Accepted
Sound of a limited wave after removing main frequency?
Fourier transform is a linear operation. This means that the infinite sinusoidal signal can be written as the sum of the sinus in the window plus the sinus outside the window. If $f(t)$ is your window ...
- 1,263
13
votes
Accepted
Can we quantify the pitch of a sound that is a mixture of many frequencies?
Short Answer:
Use the lowest of your frequencies, also known as the fundamental, to represent the pitch.
Full Answer:
First off, it seems worth noting that many sounds that consist of many frequencies ...
- 1,377
13
votes
Accepted
Is there a name for the number of '9's in numbers such as 0.999 (where it would be 3)?
I've heard 'nines' used frequently in quoting the purity of a material, and it turns out that this is a standard, though informal term. Wikipedia has this to say:
"Nines are an informal ...
- 2,504
12
votes
Sound of a limited wave after removing main frequency?
OK, so you start off with a monochromatic sinusoidal function at frequency $\omega_0$ and period $T=2\pi/\omega_0$,
$$f(t)=A\sin(\omega_0t)$$
whose Fourier transform is a pair of delta functions:
$$
\...
- 134k
12
votes
Existence of monochromatic pulses?
The fundamental reason for this is that a truly monochromatic waveform
$$
f(t) = f_0e^{-i\omega t}
$$
is active for all real times $t$ ─ it doesn't start, and it doesn't stop ─, and this means that ...
- 134k
12
votes
How exactly does a seashell make the humming sound?
While inside your house, place a shell or a cup or a drinking glass or even a cupped hand over your ear and you will observe the same phenomena. Assuming there is no significant wind inside your house ...
- 6,112
11
votes
Why does a capacitor act as a frequency filter?
What is the physical behaviour which allows a capacitor to act as a high or low pass filter?
A capacitor alone cannot act as either.
To create a filter you need a combination of resistance and ...
- 260
11
votes
Why does superposing an infinite number of waves of different wavenumbers eliminate periodicity and may sometimes result in a localised wave?
Existing answer is good. I will add some remarks which I hope may further clarify.
The question is not essentially about quantum physics. It is about the use of Fourier series and Fourier transforms ...
- 59.6k
11
votes
Avoiding radar detection using active noise control instead of a stealth fuselage
from https://doi.org/10.1109/WDDC.2007.4339412
Both answers are correct in explaining why cancelation is a bad scheme to avoid radar detection of an airplane. But repeating the incoming radar signal ...
- 19.8k
10
votes
Why are cosine and sine functions used when representing a signal or a wave?
The trigonometric functions form a basis for the space of "reasonable signals". (For the purposes of this answer, "reasonable signals" are continuous functions having finite energy and bounded power.)...
- 1,767
10
votes
What is meant by 2D fourier transform of an image?
Yeah, this can be tricky to wrap your head around! Let's simplify. I can't guarantee you'll ever have an intuition for your more complex transforms. But after reading this, hopefully you'll have a ...
- 11.9k
10
votes
Accepted
What do I hear when listening to a computer-generated sine wave?
To generate harmonics, you need a nonlinear element. Loudspeakers are not perfectly linear, so yes, they generate weak harmonics. Air is generally very close to a linear medium for sound unless the ...
- 21.8k
10
votes
Feynman claimed "The ear is not very sensitive to the relative phases of the harmonics." Is that true?
No. You just found a special case where the relatives phases of all the harmonics adds up into such a big difference in the waveform that you actually can hear it. I expect it works if the fundamental ...
- 41.1k
10
votes
Accepted
What does "DC" mean in gravitational physics?
In this specific context, DC means as other people pointed out "Direct Current." This jargon refers to the $f = 0$ component of a Fourier transform.
If you look at the definition of FT
$$\...
9
votes
Convolutions in Physics
Whenever I think of a convolution I imagine a moving average: Suppose we have a function $f(x)$ and we like to calculate the moving average using the weight function $w(x)$. What we calculate is
$$
\...
- 8,898
9
votes
Accepted
Why does a capacitor act as a frequency filter?
Imagine electricity as water in a pipe. The current can flow in either direction (direct current, DC) or one way then the other way (alternating current, AC). Now put a rubber membrane in the pipe. ...
- 106
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