Signal Processing Stack Exchange
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1500 questions
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3 answers

Fail to separate sound signals by FastICA on real-world recording

I have written a program to perform FastICA on a stereo WAV file using the code on Python MDP FastICA Example With the audio examples I get very good results. Then I try to do real world recording using two computer mono microphones connected to the…
Jeremy
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Wavelet Scattering explanation?

How does Wavelet Scattering work, intuitively? What are its motivations, and how's it differ from the (continuous) Wavelet Transform? Can it be visualized?
OverLordGoldDragon
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Approximating the frequency response of a median filter

A median filter is a non-linear and lossy process, so it doesn't have a closed form frequency response as would a FIR filter (say a box filter of the same length) in an LTI system. But how closely can something similar to a frequency response of a…
hotpaw2
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How is symbol synchronization with OFDM done?

I'm trying to understand how symbol synchronization is done in OFDM using pilot tones, cyclic prefixes, or any other technique. I've read the following answers which provide some explanation, but I still don't totally understand it. How to…
Dan Sandberg
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A DFT “periodic inputs” question

Why do people say that the fast Fourier transform (FFT) “views”, or “interprets”, or “assumes” its input sequence is periodic? I ask this question because the activities of viewing, interpreting, and assuming can only be performed by a living…
Richard Lyons
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Are there any real world applications for complex-valued signals or impulse responses?

I was just curious... $$x[n] {\longrightarrow} \boxed{h[n]} {\longrightarrow} y[n]$$ I've never seen a real world filter where the coefficient of $h[n]$ were complex, or where $x[n]$ was a complex sequence. But, the DSP book always makes a big deal…
pipen
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Inconsistency between the units of power spectral density and the definition that people often give

Perhaps someone can help me resolve something - this is my understanding: In deterministic signal analysis, for a continuous signal $x(t)$ the signal energy is defined by $$E_{\textrm{s}} = \int^{+\infty}_{-\infty} |x(t)|^2\mathrm dt \hspace{1cm}…
teeeeee
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Determining the noise floor of a signal in the frequency domain

Is there an accepted way of determining the noise floor of a signal by looking at it in the frequency domain? Is it a matter of averaging all the bins, or median, or some more complex calculation like those described in the question below? What's…
Dan Sandberg
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Any references for the trade-off between software and mechanics/optics in industrial machine vision systems?

I explain my question with a simplified example. I can design an industrial vision system for the automatic inspection of an item with these main requirements: the image of a good piece must be a black background and the piece must be grey. the…
Alessandro Jacopson
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I and Q components and the difference between QPSK and 4QAM

Both 4QAM and QPSK apparently produce the same waveform, but are they the same mathematically? In a QPSK constellation, are the mapping points at 45, 135, 225 and 315 degrees while the 4QAM is at 0, 90, 180 and 270? I also struggle to understand the…
chwi
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Interpretation of the eigenvalues of the inverse Hessian in a KLT tracker

I'm a masters student, preparing a seminar in computer vision. Among the topics is the Kanade-Lucas-Tomasi (KLT) tracker, as described in J. Shi, C. Tomasi, "Good features to track". Proceedings CVPR '94. Here's a web resource that I'm using to…
nathan g
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5 answers

Low-pass filter parameters for image downsampling

I need to downscale an image in a factor of $s_x$ horizontally and $s_y$ vertically ($s_x$, $s_y$ < $1$). I want to use a finite $n\times m$ low-pass filter before downsampling. How should I determine the low-pass filter parameters ($n, m$ and the…
Ben-Uri
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How to get Fourier coefficients to draw any shape using DFT?

I'm teaching myself about Fourier Series and the DFT and trying to draw a stylised $\pi$ symbol by fourier epicycles as detailed by Mathologer on youtube (from 18:39 onwards), and the excellent explanations with extraordinary animations by…
Chris
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Why doesn't sampling a periodic continuous-time signal yield a periodic discrete-time signal?

I have been studying signals and systems lately and I have came across the following claim: The uniform sampling of a periodic continuous-time signal may not be periodic! Can someone please explain why this statement is true?
a4w
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Converting very short "motionless" video frames to single, better-resolved, images

I made a mistake with my newly bought compact camera, before a trip to Japan. Instead of taking single pictures, I ended up with a few short "MP4" video files (1 second, 2-3 frames). I could "easily enough" extract individual frames with ffmpeg,…
Laurent Duval
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