Signal Processing Stack Exchange
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1500 questions
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What is anti-alias pre-filter for preventing aliasing after under-sampling?

We know that the under-sampling results in aliasing and frequencies higher than half of the Nyquist rate is not distinguishable. I've a base band signal that I want to use the higher frequencies which are higher than the half of the Nyquist rate…
Hossein
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Nyquist plot interpretation when curve hits the origin

I'm a bit confused about the interpretation of the Nyquist plot when the origin is part of the plot. In this case I'm not even considering closed loops, I'm just looking at the Nyquist Plot of a given transfer function and trying to relate it to the…
felipeek
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How can output sequence be equal to the sum of copies of the impulse response, scaled and time-shifted signals?

I am sorry, this is a very basic question. But i am having hard time understanding is how it is possible. I know impulse response is the output of the system when impulse sequence is given as input with initial conditions set to 0. Scaling is to…
sarbjit
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radix-4 FFT implementation

I implemented a 4-point radix-4 FFT and found that I need to do some manipulation of the output terms to get it to match a dft. My code is a pretty direct implementation of the matrix-formulation so I'm not clear on what the problem is // …
moloned
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What are some typical lossless compression ratios?

A client was trying to send me 250 GB worth of files. After attempting various ways of sharing the data, he sent me a zipped folder only 4 GB in size. That sounds like too much compression to me--I don't think when I've zipped things I've ever…
isomorphismes
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Solving Convex Optimization Problem Used for High Quality Denoising

The highest voted answer to this question suggests that to denoise a signal while preserving sharp transitions one should minimize the objective function: $$ |x-y|^2 + b|f(y)| $$ where $x$ is the noisy signal, $y$ is the denoised signal, $b$ is…
John Robertson
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Signal values we will 'miss' between sampling instances during sampling of band limited signals

According to the Nyquist–Shannon sampling theorem, any continuous time signal with a bandwidth $B$ smaller than Nyquist frequency $f_N=f_s/2$ (with $f_s$ the sampling frequency), which is sampled at sampling frequency $f_s$ can be perfectly…
Retinite
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Why images need to be padded before filtering in frequency domain

In image processing books , we are told that Images need to be padded while doing filtering in the frequency domain. Why we need that zero padding ?
Prashant Singh
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FIR filter design for complex signal

I have a complex signal generated by an impedance analyzer. What is the best approach for designing a low pass FIR filter for this? Is a real filter applied separately to the real and imaginary streams optimal for this or do I need a…
Max Yaffe
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Why calculate negative frequencies of DFT?

This answer says that when calculating the DFT on a real valued signal, the (roughly) second half of the bins are the complex conjugates of the first half of the bins. Firstly I was curious if that is true? If it is true, it seems like for frequency…
Alan Wolfe
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Segmenting pills from the background

I just recently started out with Image processing and taken up a course related to it in Grad school. But I already have a project to do without too much information about the subject, however I've made some steady progress. I am trying to segment…
GamingX
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Estimating velocity from known position and acceleration

I am stuck at modeling a system model, i.e. getting my state vector and input vector. My guess is that position and velocity are state vector and acceleration is input vector. My 2nd guess is that all three quantities are in state vector and none in…
c0dehunter
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Deep space communications BER and FEC?

What kind of bit error rate do they get from deep space communications (Pioneer, Voyager, et.al.), and what kind of modulation and FEC allows them to recover messages with that microscopic level of received signal power? Are there more modern…
hotpaw2
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Image Processing Prior to Feature Detection

I have implemented a feature detector based on Harris corners. It works fine most times, but there are cases where it performs poorly. I need to make it work on many different images without configuring it individually. The problem is with the…
Libor
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Why are QAM Constellations regular and rectangular?

In most IQ graphs of QAM noise, it seems like the constellation ends up with more distortion the farther you get from the center: What causes this non-linear distortion, and why are QAM constellations not shaped like the following?
Mitch
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