Signal Processing Stack Exchange
Signal Processing Stack Exchange

Questions tagged [physical-units]

18 questions
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What are the units of my data after an FFT?

Magnetometer measures the derivative of the magnetic field, or dB/dt, with an output in microvolts (mV). The Sampling rate is 128 Hz, so if we collect data for 2 minutes, $2 \times 60 \times 128=15360$ points (discrete case). When I perform an FFT…
MikiBelavista
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What is the difference between the PSD and the Power Spectrum?

Can any one explain the difference in the amplitude between the two and what does each one represents? For example, when using the pwelch algorithm in MATLAB how do the two different options ('psd','power') affect the units of the output? (I know…
havakok
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Making the units of a analytically calculated PSD consistent with the units of an FFT

One thing that has always puzzled me is making the units of an analytically derived Power Spectrum Density (PSD) consistent with the units of an FFT. Let's say we record the output of a frequency generator, which we just set to output a signal of…
Q.P.
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Unit of Energy Spectral Density

The continuous-time Fourier Transform (CTFT) of a signal $x(t)$ (with unit $unit$) is: $$X(\omega)=\int_{-\infty}^{\infty} x(t)e^{-i\omega t}dt$$ which should be in $unit\cdot sec$ or $\frac{unit}{Hz}$. The Energy Spectral Density (ESD) of $x(t)$ is…
JZYL
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Fourier Transforms, Convolution, Cross-correlation: what is their physical unit exactly?

Let us assume we are talking about real, deterministic, electrical signals $x(t)$ and $y(t)$ (magnitude in Volts). There are different kind of Fourier Transforms. I made a table to summarize: NB: By the "<-" symbol, I mean variable substitution. I…
lostdatum
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Changing units in Fourier filtering

I'm applying a radial low-pass filter on a $H{\times}W$ pixel 2D image $I$ where $H \neq W$. To implement this filter, I apply 2D DFT to $I$ to produce $I'$, the $H{\times}W$ frequency domain representation of $I$. I apply an element-wise…
tmakino
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Units for a PSD from square of FT?

If I am looking to do a PSD plot on a signal $x(t)$ with units $m$ then the units I am expecting in the PSD would be $\frac{m^2}{Hz}$ but I can't seem to get this result from the following reasoning: If we consider the fourier transform $$ F(k) =…
Stephen Jackson
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Correct SNIR computation units

I would like to know the correct units to make a SNIR computation. I am using the following formula: $$ \text{SNIR} = \frac{1}{\frac{1}{\text{SNR}} + \frac{1}{\text{CIR}}} $$ I have SNR in dB and CIR in dBm. Shall I convert SNR to dBm to get the…
pablo
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Convolution Input/output Units

How come are the units of convolution for LTI system not consistent? $$y(t)= \int_{-\infty}^{\infty} x(\tau)h(t-\tau)d\tau$$ $y(t)$ unit is volt, whereas the RHS has volt.time unit!!!!
HYMD
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Why is "$1/\mathrm{Hz}$" unchanged while converting$\mathrm{V}^2/\mathrm{Hz}$ to $\mathrm{dB}/\mathrm{Hz}$?

When computing power spectral density via Fourier transform and Parseval's theorem, one gets units of $V^2/Hz$ (e.g. Wiki). As a popular next step, the following unit conversion is widely used: $V^2/Hz \to dB/Hz$, and it's done by taking the famous…
agronskiy
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What is the unit of velocity calculated using Savitzky–Golay filter?

I have data from an eye tracker collected while subjects were doing a saccadic task (i.e. fast eyes movements). Specifically, I have the position (in degree) on the x and y axes, collected at 120Hz. My aim is to find the saccades relative to the…
fednem
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Units of PSD converted from spatial to temporal frequency

I am putting together some simple ride comfort models that use road surface PSDs from ISO 8606 (road surface profiles) as inputs to a quarter car suspension model to produce body acceleration spectra. These are then weighted according to ISO 2631…
Simon Aldworth
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Creating the frequency-spectrum with VC-curves for Building Vibrations measurement

I'm very new to signal processing and can't get ahead: I'm using an Accelerometer to measure the acceleration of i.e. the building vibrations or elements/machinery etc. For creating the spectrum, I complete a fft, with python's numpy, and there…
Wolfmercury
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Loss of precision due to low-pass filtering in physical units

Suppose I have a $10{\times}10$ pixel image, where each pixel represents 1 mm in physical units, and I apply a Gaussian low-pass filter with $\sigma = 5$. Can I make any statements such as "the maximum level of precision in the original image was 1…
tmakino
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What are the ranges of values for each audio feature/descriptor?

I need to normalize some audio feature measurements I've done with the software Wolfram Mathematica. Coming from a non signal processing background, I have some difficulties understanding what several audio features are actually measuring and thus…
Mumen Raida
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