All Questions
Tagged with signal-processing acoustics
59
questions
7
votes
5
answers
2k
views
How exactly does a seashell make the humming sound?
My little brother asked me where the ocean-like sounds came from inside of a sea shell. I told him that the air trapped inside the shell vibrates, making a sound. But then he asked me why the air had ...
- 12.5k
12
votes
8
answers
5k
views
Feynman claimed "The ear is not very sensitive to the relative phases of the harmonics." Is that true?
In The Feynman Lectures on Physics, Dr. Richard Feynman claimed that the ear (I assume he meant the human ear) is not sensitive to the relative phases of harmonics.
However, I was asked to test ...
- 145
1
vote
1
answer
54
views
How to justify sound propagation is a linear time-invariant (LTI) system?
Background
A linear time-invariant (LTI) system (black box) is one described by the system:
\begin{align}
\dot{\xi}(t) & = A\xi(t) + B\omega(t), \; \xi(0) = 0 \label{eq-abc-1}\\
\lambda(t)...
- 151
0
votes
0
answers
27
views
Comparison between wave equation theory and transfer function theory
I deal with analysis of acoustic signals in solids. And after some literature research in physics and mathematic, I have a question about the followings two theories:
Wave equation theory: Imagine I ...
0
votes
0
answers
21
views
FWHM and Beam Width of transmitted beam of ultrasonic (ultrasound) transducer
Im a studying ultrasonic transducer and I got a question about FWHM and Beam Width while solving some problems.
In the lecture, I learned that Beam width is calculated by:
$2\Delta\theta = \frac{3.8\...
- 43
10
votes
6
answers
3k
views
Can sound waves be modulated?
Can you modulate sound waves? Like can you have a sound wave of a relatively low frequency and modulate it with a sound wave of a much higher frequency which people cannot hear and send it through the ...
- 101
0
votes
0
answers
24
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Is the strongest acoustic signal always the closest?
I have a single beam echosounder that I use to measure the distance to an object underwater. It emits an acoustic pulse and listens to the reflections. Using the time of flight and the strongest ...
- 1
22
votes
12
answers
8k
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How do computers store sound waves just by sampling the amplitude of a wave and not the frequency?
All of this just doesn’t make sense though.
I mean, doesn’t the amplitude represent the loudness and the frequency the pitch? Aren’t they completely independent from each other?
Is the book just ...
- 390
12
votes
3
answers
4k
views
Avoiding radar detection using active noise control instead of a stealth fuselage
was reading about different stealth technologies used by modern aircrafts to avoid radar detection.
Wouldn't it be easier to have a receiver on the airplane listening on the radar frequencies and then ...
- 131
1
vote
0
answers
86
views
Modeling an Acoustic Reflection from a Wall
I am trying to simulate the reflection of a sound ray, that goes from a sound source, bounces off a wall, and is received by a microphone.
The wall has a an absorption coefficient, and a specular ...
- 11
0
votes
1
answer
145
views
What is the physical meaning of the pressure of an acoustic point source being complex?
Context
From various sources of Acoustics (such as "Acoustics -
An Introduction to Its Physical Principles and Applications" by Allan D. Pierce and "Fundamentals of General Linear ...
- 1,785
1
vote
1
answer
215
views
Why don't podcasts played at faster speeds sound higher-pitched?
Many podcast apps allow you to listen to podcasts faster than the speed at which they were recorded (typically at x1.25, x1.5, x1.75, and x2 speeds).
If these apps are simply replacing the sound's ...
- 48.4k
0
votes
1
answer
58
views
Can multi-instrumental sound be reconstructed from a waveform?
This question came about when I saw someone wearing clothing with a waveform on it. I wondered if it would be possible to reconstruct the original sound from the printed waveform.
I understand that a ...
- 101
2
votes
3
answers
522
views
Why does audio signal amplitude always fall off at higher frequencies?
In the frequency spectrum of every real audio sample that I've ever seen, the amplitude of the frequency components is always higher at low frequencies, then rapidly falls off at higher frequencies.
...
- 1,004
7
votes
2
answers
561
views
What do I hear when listening to a computer-generated sine wave?
When I use a sine-wave generator (such as this one), I give credit to the software and my hardware that a pure sine wave is produced (as close as is technologically possible) — that is, no harmonics. ...
- 173
3
votes
2
answers
73
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In what respect does the wave pattern of a noise and music differ?
Does the wave pattern of musical sounds contain only harmonics (other than the fundamental frequency) while noise contains random overtones (that are not harmonics)?
- 1,064
1
vote
2
answers
85
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Signal Processing – Discrete Fourier Transform and Incomplete Fourier Series
I'm working on a paper where I'm collecting sound pressure data from a chord's wave and trying to create a frequency spectrum to find the individual frequencies that make up the chord.
However, I can'...
- 13
19
votes
6
answers
3k
views
Can we quantify the pitch of a sound that is a mixture of many frequencies?
How is the pitch of a sound defined quantitatively when it is a mixture of many frequencies? For example, the sound emitted by a plucked guitar string, or say, the pitch of somebody's (normal) voice. ...
- 11.8k
1
vote
0
answers
37
views
Difference Between a Time-Domain and a Simulation Domain Acoustic Pressure Simulation
I would appreciate it if someone would be able to clarify my doubts. I'm currently working on acoustic simulations in COMSOL and is currently confused on the information provided by the simulations ...
- 11
1
vote
2
answers
163
views
Is the human singing voice different from a linear, time-invariant (LTI) system?
Typically the human voice is modelled by a linear, time-invariant (LTI) system.
An LTI system cannot add any frequency components to an input signal. This is obvious from the input-output relation in ...
- 111
2
votes
1
answer
381
views
Why can't you filter out the sound of running water using noise-cancelling software?
The book "Clint Emerson - 100 deadly skills", a fun illustrated book of spy techniques claims the following:
Deadly skill No 054, Civilian BLUF:
While noise-canceling software can override ...
- 143
1
vote
1
answer
96
views
Can we decompose sound like white light is decomposed (dispersed) in different colors?
When we send white light through a prism, the light is decomposed in the colors that constitute it due to the different velocities which different frequencies. Is there a way to decompose "white ...
0
votes
0
answers
66
views
In square wave modulation: should the low frequency part of the graph not take place in the low amplitude part of the pulse?
I try to get my sound program right, and hoped to find some help here with the understanding of frequency modulation by a square wave.
My modulation looks like this: (please excuse if my formula ...
- 101
-2
votes
1
answer
2k
views
Why does a running fan causes some soundproofing in the room?
I notice that when I switch on my fan inside my room, the room becomes soundproof to a great extent to the outside noises. The greater is the speed of the fan, the greater is the soundproofing.
When ...
- 2,517
2
votes
1
answer
43
views
Why are an audio signal and its cochlear response modelled as two-dimensional variables?
According to Eguíluz et al, amplification of an incoming audio signal by the human ear can be described by a supercritical Hopf-bifurcation
$$\dot x(t) =(\lambda-i\omega_0-|x(t)|^2)x(t)+S(t),$$
...
- 121
0
votes
1
answer
103
views
How to solve this problem involving the "longest interval"?
The problem is shown as follows:
If one wants to make a digital record of sound such that no audible information is lost, what is the longest interval, $\Delta t$, between samples that could be ...
2
votes
0
answers
86
views
The validity of some "applications" of the uncertainty principle
Given a $L^2$ function $f$ with $\int_\mathbb{R}xf(x)dx=0$, define its variance to be $\sigma_f^2=\int_{\mathbb R}x^2f(x)dx$. The uncertainty principle states that $\sigma_f\sigma_\hat f\geq 1/4\pi$,...
- 1,335
2
votes
3
answers
313
views
Can a sound wave begin with rarefaction?
Some digital recording samples (audio files) of recorded acoustic sounds present sound waves which begin with rarefaction. Is this an actual phenomena that can occur or is it a result of sound ...
- 23
1
vote
0
answers
63
views
Fourier Coefficients
Suppose i've a two voice samples v1 and v2. Comparatively voice v1 is louder than the v2. If both the voice is spoken by the same person.(Spoken normally as he speaks)
Is it good to state the ...
- 121
1
vote
2
answers
147
views
How does ultrasound work? How is the signal processed?
Why is ultrasound 2D? Is there a way of making ultrasound 3D without piecing together 2D? How close is ultrasound to sonar?
- 6,044
1
vote
1
answer
99
views
Multilateration of Sound in 3D Space
TL:DR - How can you find the 3D coordinates of a emitter than transmits an impulse signal?
STORY:
I'm working on something to improve my bird-watching. I've got a camera that can take pictures of ...
- 111
3
votes
1
answer
70
views
Sound an amplifier makes when you plug / unplug a cable [closed]
When you plug, unplug or even touch a jack cable of an aplifying system with speakers, one can hear a low-pitch sound that is of roughly always the same frequency, which does not seem to depend on the ...
- 2,469
1
vote
2
answers
61
views
Recognizing speech at 1bit quantise depth?
i found on german wikipedia an audio example of 1 bit depth quantising, where the speech still can be recognized. how is it possible if at 1 bit depth we have just two values: "signal" and "no-signal"?...
- 11
0
votes
1
answer
124
views
Acoustic power spectral density change due to diffraction
Say we have an acoustical point source emitting white noise - i.e., a power spectral density of $$S_x(f) = \frac{N_0}{2}$$ The source is embedded in the plane such that it radiates in half-space - i.e....
- 1,200
2
votes
1
answer
1k
views
Larsen effect and pitch of sound
Why Larsen effect produces always high pitched sounds, never low pitched?
- 1,343
0
votes
1
answer
156
views
Interpreting FFT background noice
There is some construction down my street and I think the drills are putting off a high pitch noise so I downloaded a spectrum analyzer. they have an FFT plot here:
The "57-dB-A" I guess is the ...
- 101
2
votes
7
answers
4k
views
Can human ear distinguish between sounds of different phase?
A noise cancelling headphone produces a sound that's out of phase with ambient noise, mixes them and hence cancels them.
But I wonder if we were to hear the 2 sounds which are out of phase to each ...
- 131
9
votes
4
answers
3k
views
Sound of a limited wave after removing main frequency?
From my old studies in signals I can remember that "a signal limited in frequency domain is unlimited in time domain" and viceversa (a signal limited in time domain is unlimited in frequency domain).
...
- 737
0
votes
1
answer
59
views
Subtracting Audio from a Song with Multiple Forms
This question may start oozing into the realm of copyright infringement, but let's discuss the theory first and foremost.
I have a song with vocal and orchestral accompaniment from a well-known movie ...
- 109
1
vote
1
answer
337
views
Acoustical Design considerations for Active Noise Cancellation Project for Air vent [closed]
I am working on ''Active noise cancellation for air vent'' project. I am
using NI myRIO1900, Audio Technica ATR 3350 omni directional microphones
and Tevion Loudspeakers. I have done the programming ...
- 111
1
vote
3
answers
7k
views
Do electromagnetic waves produce sound?
Preamble:
At 5 AM in the morning, if I sit quietly and listen attentively, I can hear many different noises, on a very high frequency. If I try to isolate the ones that are less noisy, I can clearly ...
- 1,793
0
votes
1
answer
196
views
How can one change the virtual position of a sound source with a fixed array of speakers?
I have a question about signal processing:
How to make a person, sitting between array of two loudspeakers (one from the left and one from his right), hear the sound that came from both loudspeakers, ...
- 109
1
vote
2
answers
153
views
How do phase carries structural information about the function? [closed]
Suppose you are on a railway platform and you hear the sound of train coming towards you. Now, Using Fourier transformation we can convert the time domain function (here take sound as a function) ...
- 133
4
votes
1
answer
667
views
Significance of higher harmonics
I am analyzing a noise signal and have identified the fundamental frequency of a tone and it's higher harmonics. Say for example given the signal below,
The fundamental frequency has a sound pressure ...
- 41
1
vote
1
answer
170
views
Two superimposed sounds traveling through low- and high-density matter: is separation possible?
Two superimposed sounds (at source: $s(t) = s_1(t) + s_2(t)$; the two sound components overlap completely in time, partially in spectra) travel through low- and high-density matter and are recorded ...
- 113
0
votes
2
answers
1k
views
Why need for 96kHz, 192kHz audio? [closed]
Human can hear 20-20,000 Hz waves, so by Nyquist theorem it's sufficient to sample audio with 40 kHz. Indeed, 44.1 kHz widely used. But what do we need higher sample rates for? 96 kHz, 192 kHz are ...
user22330
1
vote
2
answers
6k
views
Compression vs Rarefaction in Sound Waves
I am currently looking into solutions for Sound Classification, and I came across Ludvigsen's methodology (if anyone wishes to refer to it).
The problem is that a sample graph of amplitudes in one of ...
- 13
0
votes
0
answers
39
views
A sonar continuously emits x(t), a general but known waveform and is reflected by a target. hypothetical question
A sonar continuously emits x(t), a general but known waveform that is reflected by a target and received by the sonar. Both the sonar and the target move in the 3-dimensional space in a general but ...
10
votes
2
answers
1k
views
Why does a wall act as a low-pass filter?
Learning about the fourier transform and its connection to filtering/convolution got me curious about naturally occurring filters.
Why/how is it that brick walls naturally act as a low-pass filter (...
- 101
1
vote
1
answer
737
views
Is there any way to find difference between two same sounds of different people? [closed]
I am trying to understand and find a way to distinguish two same sounds of different people by some physics formula, so could you guys help me?
OK I'll try to explain my question in this way that, ...
- 121