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Questions tagged [signal-processing]

The subfield of electrical engineering that focusses on analysing, modifying, and synthesizing signals such as sound, images, and scientific measurements.

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Phase Slope Distance Calcuation

After trying to implement IFFT algorithms for phase-based ranging, as outlined in this very interesting and descriptive blog post; I've been getting horrendous results (orders of magnitude inaccurate),...
Hysan Happy's user avatar
3 votes
3 answers
77 views

Why the $T_1$ recovery & $T_2$ decay are independent?

In MRI, I was thinking that the decrease in transverse magnetization results in the recovery of longitudinal magnetization. However, recently, I found it was wrong. I saw a diagram (McRobbie 2014. ...
COTHE's user avatar
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7 votes
5 answers
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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 ...
AlphaLife's user avatar
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2 answers
151 views

Weird looking sine wave behavior in an electric circuit

while studying an RLC circuit I noticed some weird like sine waves at low frequencies (1-9 kHertz) on the inductor, The amplitude behavior did not follow the theoretical model. Instead, suggested the ...
dareen's user avatar
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5 votes
2 answers
2k views

What does "DC" mean in gravitational physics?

I have came across a few works in gravitational physics using the term "DC" without further explanation of its meaning. For example, consider Strominger's 1703.05448, which states in p. 2 ...
Níckolas Alves's user avatar
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1 answer
69 views

How to solve the transient response of a general $RLC$ network?

There is a $RLC$ network $\{V_i\}$ with a complex impedance $Z_{ij}$ on each edge. all vertices have initial voltage $V_i$ and all edges have initial current $I_{ij}$. Now, is there a general way to ...
ZhenRanZR's user avatar
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2 votes
2 answers
53 views

How can I determine an error on total noise?

I am analyzing the data for an experiment, where we measured the total noise in a system. The total noise is defined as the variance of the signal (and is equal tot the integral over the noise ...
LemanRussNL's user avatar
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Fourier Transform of periodic Signals

If $f(x)$ is a periodic signal with a period $A$ then the Fourier transform of the signal $F(k)$ is zero, unless $k A$= $2 \pi n$ where $n$ is an integer. How can there Be a Fourier transform of a ...
Hello's user avatar
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8 votes
1 answer
2k views

Is there a name for the number of '9's in numbers such as 0.999 (where it would be 3)?

I am doing an optics simulation involving transmission and reflection coefficients very close to 1, such as 0.999. While I was an undergraduate student, a professor mentioned that, in certain fields, ...
jcuk's user avatar
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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 ...
Dan Bullard's user avatar
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1 answer
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Phase-Based Ranging

I've been reading a lot about Phase-Based Ranging (PBR), and it's all starting to become very intuitive. BUT; There is one technical, but extremely important, detail that seems to escape me. When the ...
Hysan Happy's user avatar
2 votes
0 answers
44 views

How to extract the "matter fluctuation amplitude" from the CMB power spectrum?

How do you convert the value listed in Planck 2018 results. VI. Cosmological parameters, $A_s = 2.101\times10^{-9}$ to the value of the matter fluctuation amplitude $\sigma_8=0.8111$? I tried ...
Finerichmen's user avatar
1 vote
0 answers
25 views

Signal recovery limits, magnetic

This question is about signal recovery. I am interested in what is the best that has been done so far, in the case of a signal of known form and which is not simply a sine wave, and what might in ...
Andrew Steane's user avatar
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1 answer
33 views

What relationship between the time recording length and the frequency bandwidth?

In model testing for ocean waves, the data recording duration is usually longer the better especially for irregular waves. The recording length shall be long enough to achieve sufficiently small ...
MathArt's user avatar
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2 answers
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I don't understand intuitively why the instantaneous frequency is obtained by calculating the time derivative of the phase

I don't understand intuitively why the instantaneous frequency is obtained by calculating the time derivative of the phase
krunker.io's user avatar
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2 answers
85 views

Does sunlight have a modulation frequency?

By frequency, I don't mean electromagnetic frequency, I mean modulation frequency. For example, I can put a PWM square wave on an LED at some frequency, which I can detect with a photodiode and a ...
Ben S.'s user avatar
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28 views

Using Long-pass Filters with Gaussian Edges to Measure an Optical Spectra

Imagine you have some optical spectra (intensity vs wavelength) you want to measure. You do so by measuring the intensity of the spectra hitting a detector after placing multiple long pass optical ...
Will Braun's user avatar
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Continuity of a quantity in a conical system to determine the velocity field

My research is on radar images and the images are collected in several conical surfaces. These conical surfaces have the same origin, the same maximum length (max flare or max range), but different ...
CfourPiO's user avatar
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)...
César VB's user avatar
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0 answers
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Pulse to sine with the same frequency

I have a pulse signal with frequency f(t) And i want to generate from it a sine signal with frequency f(t) (f(t) doesn't vary a lot in time) Is there a method to do it directly with a function ...
mahboul 3's user avatar
1 vote
1 answer
89 views

Kramers-Kronig relations for a Gaussian function

Consider a function of a complex variable $\omega$ which is given by $f(\omega) = e^{-\omega^2/2}$. This function is symmetric, holomorphic everywhere, and vanishes as $|\omega| \rightarrow \infty$. ...
user19642323's user avatar
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Second-order variation of an integral

I was reading the paper SISAR Imaging for Space Debris based on Nanosatellites, in which the Fresnel-Kirchoff diffraction formula is applied for a scenario in which the receiver, transmitter and ...
DaDSPGuy's user avatar
2 votes
1 answer
49 views

How a switching mixer works in this example circuit?

I am reading about lock-in amplifiers and came across this example circuit of a mixer: You have one sinusoidal input signal $e_1$ with a phase $\phi_1$ and the local oscillator has a square-wave ...
NeonGabu's user avatar
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0 answers
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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 ...
Ronghua Xu's user avatar
1 vote
2 answers
47 views

Is it possible to, like white noise, excite all audio frequencies equally, but with a more immediate & less random burst? Like a signal discontinuity?

I am trying to generate an audio signal that, like white noise, has "equal intensity at different frequencies, giving it a constant power spectral density", but unlike white noise, can be ...
mike's user avatar
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0 answers
20 views

Does it make sense to whiten the data in order to apply a matched filtering algorithm if my dataset consist of a sinusoid + random Gaussian noise?

With a Python program I generated a sinusoid signal and I added to it Gaussian noise. Now I want to compute the optimal SNR by applying a matched filtering algorithm. Since the noise is white (at ...
AleNekro97's user avatar
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0 answers
35 views

Feedback control system in gravitational wave detectors

I am preparing for a seminar on ground-based gravitational wave detectors. One topic I have very little idea about is feedback control systems. I have a basic knowledge of it, but I need to read some ...
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\...
COTHE's user avatar
  • 43
2 votes
1 answer
123 views

Where can I learn Fourier analysis and complex signal processing for quantum mechanics?

I'm requesting resourses to dive deep and get a good grip on complex signals, Fourier analysis and connections to information theory and information encoded by complex signals. My background: 3rd year ...
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 ...
Denis McCarrick's user avatar
1 vote
0 answers
25 views

Two-Ray Ground-Reflection Model: Understanding the Difference in Phase Offsets at the Receiver

Currently, I'm trying to understand the Two-Ray Ground-Reflection Model. During my research, I came across the following simplification expressing the received power as follows (taken from Wikipedia): ...
Henerii's user avatar
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0 votes
0 answers
24 views

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 ...
Apo's user avatar
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0 votes
1 answer
66 views

How do you extrapolate frequency data from FDTD simulation time data?

Context: Im a PhD student who plans on doing research in theoretical plasmonics/nanophotonics, so I am studying up on understanding FDTD. I am having a bit of a conceptual issue regarding ...
ahrensaj's user avatar
22 votes
12 answers
8k views

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 ...
RedP's user avatar
  • 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 ...
Henry Skoglund's user avatar
0 votes
1 answer
70 views

Doubt on time invariant system

Now I am delaying the output of a system (which takes $x \left( t \right)$ as input and gives $t \cdot x \left( t \right)$ as output) by $T$ then final output is: Let's denote the output of the ...
Qwe Boss's user avatar
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 ...
Mason Wang's user avatar
0 votes
1 answer
144 views

Energy spectral density vs power spectral density vs power spectral density per unit time

I recently started research to measure the voltage noise spectrum of materials to study their phase transitions. Before understanding physics, I am now confused by the three terms used in literature: ...
Yuxin Wang's user avatar
1 vote
1 answer
51 views

Determining the location of light receivers using signals propagating in anisotropic media

Problem. I have a set of $16$ light receivers with entirely unknown locations, and a pair of light transmitters with exactly known locations. One light transmitter is stationary, and located near to ...
MomentumEigenstate's user avatar
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 ...
ZaellixA's user avatar
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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 ...
tparker's user avatar
  • 48.4k
7 votes
2 answers
1k views

Why does superposing an infinite number of waves of different wavenumbers eliminate periodicity and may sometimes result in a localised wave?

I am studying how wave packets are defined in quantum mechanics, but I am finding it hard to intuitively understand why superposing an infinite number of waves of different wavenumbers $k$ may ...
cookiecainsy's user avatar
0 votes
1 answer
126 views

The solar spectrum on the time domain

This is the solar spectrum by wavelength: By formula $c=f\lambda$, we can plot the solar spectrum over the frequency domain: Then we can conduct inverse Fourier transform to transform the plot into ...
LianNuo 's user avatar
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 ...
mikemaccana's user avatar
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0 answers
114 views

Why do the signals for second harmonic generation and third harmonic generation differ in the strong focusing limit (strongly focused gaussian beam)?

In Ward & New (1969), the expression for second harmonic generation (SHG) and third harmonic generation (THG) intensity is derived for the focal volume of a strongly focused gaussian beam (axially ...
A mindful mundu's user avatar
0 votes
1 answer
71 views

Recovering Decay Constant from Fourier Transformed Exponential Decay in NMR

I'm currently in a NMR lab for an undergraduate physics class, and I am attempting to determine the decay constant $\tau$ (e.g. $T_2$) associated with a free induction decay signal. However, our ...
ZSpoke's user avatar
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0 votes
1 answer
86 views

It is possible to express the convolution between two quantum functions $\psi_{1}(x)$ and $\psi_{2}(x)$ in terms of a inner product?

The question of the title is due to the following methodology. Let us consider two arbitray quantum functions $\psi_{1}(x)$ and $\psi_{2}(x)$, such that the convolution between them is $$\left\lbrace \...
Julio Abraham Mendoza Fierro's user avatar
1 vote
0 answers
41 views

Spectral representation of a white stationary process

I am trying to better understand the spectral representation of stochastic processes. From the book "Spectral Analysis for physical applications" by Walden and Persival: The spectral ...
Chachni's user avatar
  • 111
2 votes
3 answers
523 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. ...
Jason C's user avatar
  • 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. ...
Aaron's user avatar
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