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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 ...
Solomon Slow's user avatar
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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 ...
Pritt Balagopal's user avatar
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 ...
niels nielsen's user avatar
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'...
knzhou's user avatar
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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 ...
Joel Keene's user avatar
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 ...
DKNguyen's user avatar
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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 ...
Nuclear Hoagie's user avatar
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 ...
hyportnex's user avatar
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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....
Solomon Slow's user avatar
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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 ...
Farcher's user avatar
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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 ...
mmesser314's user avatar
  • 45.7k
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). ...
John Doty's user avatar
  • 21.9k
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 ...
John Doty's user avatar
  • 21.9k
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 ...
hft's user avatar
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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 ...
Thomas Blankenhorn's user avatar
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 ...
user34722's user avatar
  • 3,195
13 votes
Accepted

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 ...
KDP's user avatar
  • 10.1k
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 ...
Emilio Pisanty's user avatar
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 ...
user9413641's user avatar
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 ...
Andrew Steane's user avatar
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 ...
hyportnex's user avatar
  • 20.4k
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.)...
Eric Towers's user avatar
  • 1,777
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 ...
Gilbert's user avatar
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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 ...
John Doty's user avatar
  • 21.9k
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 ...
mmesser314's user avatar
  • 45.7k
10 votes

Feynman claimed "The ear is not very sensitive to the relative phases of the harmonics." Is that true?

The way hearing works is that acoustic vibrations that reach you inner ear cause mechanical vibrations of the so-called hair cells inside cochlea. Different hair cells happen to have different sizes ...
John's user avatar
  • 4,193
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 $$\...
AtomicUserOverTheFields's user avatar
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 $$ \...
NotMe's user avatar
  • 9,294
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. ...
dmstraker's user avatar
  • 106
8 votes
Accepted

Rope as Communication Media

If you want to use this as a link between standard computers or microprocessors you will have to design and build a encoder to turn voltage levels into signals on the rope at the transmitting end and ...
gandalf61's user avatar
  • 60.4k

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