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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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 $|\omega| \rightarrow \infty$. ...
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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 ...
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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 ...
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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
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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 ...
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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 ...
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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 ...
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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\...
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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 ...
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6 answers
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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 ...
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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): ...
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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 ...
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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
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12 answers
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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 ...
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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
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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
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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
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What are the applications of fractional convolutions to physics - if any?

There are multiple applications of the convolution operation to physics. For instance, it comes about in calculations in fluorescence spectroscopy, acoustics, and computational fluid dynamics. The ...
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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
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1 answer
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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
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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 ...
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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. ...
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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. ...
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How to convert from a wave-reading?

I have a series of wave-readings which show wave amplitudes pr. time unit for different events. So on the $x $-axis we have seconds, and on the $y$-axis, wave height. If I want to convert this to a ...
Luthier415Hz's user avatar
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What's the formula of SNR (Signal to Noise Ratio) to dipole antenna array (eg, LOFAR) look like?

It was wellknown that the SNR of single dish telescope reads $$s/n=\frac{P_s}{P_n}=\frac{P_{s}}{T_n}\sqrt{\frac{t}{B}},$$ where $P_s$ is the collected power, $T_n$ the noise temperature, $t$ the ...
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3 votes
2 answers
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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)?
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Minimum Observable Offset Frequency in Leeson's Formula

It has been argued in some publications that the age of the universe represents a lower limit on observable frequencies (in their paper, corresponding to a value of $10^{-17}$ Hz). The authors do not ...
CuriousDroid's user avatar
16 votes
5 answers
3k views

Fourier vs. Laplace transforms

Electronics books often use Laplace to analyze circuits, while in physics we use Fourier, most of the times... if not always: from complex impedances to electromagnetism, quantum mechanics, Green ...
Ste's user avatar
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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'...
Dr. Math's user avatar
5 votes
1 answer
176 views

What's the smallest signal to noise ratio for which a signal has been extracted?

Suppose we have some physical variable $y$ that is changing in some way and we want to detect this change in the presence of noise (e.g. white noise) in that same physical quantity. For example $y$ is ...
Andrew Steane's user avatar
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How to "classify" signals?

I have some signals and I want to classify them into different types. Signals are all sine shape signals, some might have glitches. I know I could classify them base on frequency or amplitude, but is ...
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Accidental coincidence formula

Suppose you have a setup with $n$ scintillators coupled with $n$ PMTs. These signals are passed to a discriminator. I am observing some signal, let's say this signal is coming from cosmic rays and I ...
Matteo Brini's user avatar
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Can you make a faraday cage intended to effect electrical wires?

Generally with a faraday cage your object is completely surrounded and encapsulated within the cage. Let's say I have a wire with electronic signals flowing through it, say an ethernet cable that is ...
AskedSuperior's user avatar
1 vote
0 answers
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Confusion with spectral density of the emitted power of blackbody radiation

I'm reading a book discussing electrons' velocity fluctuations, which would cause electronic noise when detecting signals. Velocity fluctuations originate from thermal motion. Superimposed on the ...
Lluvio Liu's user avatar
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1 answer
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Data transmission via laser illuminating the ceiling

I've heard a data transmission technique proposed more than once wherein a base station would fire a laser at the ceiling of an indoor space. The pulsing of this laser would be observed by one or more ...
user22919's user avatar
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1 answer
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Evaluate action of $f(\frac{d}{dx})$ using the Fourier/Laplace transform

Initially I asked this question on mathoverflow. I however thought physicists may face this sort of problem more than mathematicians (I am an engineer). Due to that, I decided to ask here as well. ...
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Understanding Upper Side Band (USB) and Lower Side Band (LSB) of Modulated signal

I want to know that what is UPPER SIDE BAND and LOWER SIDE BAND in this picture? I have a confusion that the portion above the x axis is the USB and the portion below the x axis is LSB. I have doubt ...
mainak mukherjee's user avatar
1 vote
1 answer
52 views

Wavelength and frequency associated with a wave pulse

What are the definitions of wave length and frequency of a wave pulse?
Ahmed Samir's user avatar
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1 answer
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Sensor Array Position Calibration in Anisotropic Media

Problem. I have a sensor array consisting of $n \gg 4$ receivers at unknown locations $\langle x_n, y_n, z_n\rangle$ embedded in an anisotropic medium whose index of refraction varies as a known ...
10GeV's user avatar
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1 vote
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Maximum bitrate density of a shared medium

I'm not a physicist, so my apologies if this isn't worded correctly, or if it even is a valid question. I was recently learning how WiFi works and how the slowest devices on a channel can slow down ...
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What would happen when two wave functions intersect in a Fourier series representation of periodic signals? [closed]

I saw a piece of code on github which transforms the planetary movement into the fourier wave function. These circles are given by the x and y ordinates: x=cos(ωt) y=sin(ωt), which are periodic. ...
Kevin's user avatar
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How do I convert the Amplitude from Power/Amplitude spectral density?

I've started working on PSD for seismic signals. In theory, PSD signal can be expressed in 2 ways. One in $(PSD=g^2/Hz)$ and other in $PSD=((meter/second^2)^2/Hz)$ and also ASD=(√PSD). Here $g$ is the ...
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