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Questions tagged [aliasing]

In signal processing and related disciplines, aliasing refers to an effect that causes different signals to become indistinguishable (or aliases of one another) when sampled.

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Why does the frequency sampling method for FIR filter design operate in this manner?

I'm studying FIR filter design and it's time for the frequency sampling method, my teacher said that to use this method you need to follow the following steps: Sample the periodic frequency response ...
minghierid's user avatar
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Would an image sensor with photosites arranged irregularly to reduce aliasing be feasible?

I’m guessing it’ll be more computationally complex considering the irregularly sampled image would have to be converted to a regularly sampled one and probably a different demosaicing algorithm would ...
LucaMancini's user avatar
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How does the sampling rate of a digital filter limit the sampling rate that can be used for replay of filtered signal?

I need a band-limited white noise to characterize a biological sensor that senses mechanical movement. For that, I am generating a Gaussian white noise (MATLAB Communications toolbox) of length 10 ...
chinmayeelm's user avatar
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2 answers
80 views

Benefit of Anti-Aliasing for Wideband Finite Time Duration Signals prior to Sampling

Most literature about sampling explains the need for anti-alias filters in terms of periodic signals, preventing a periodic signal with frequency greater than half the sampling frequency from ...
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1 answer
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Effect of aliasing on time-domain SNR

I'm trying to reconcile the fact that decimation without low-pass filtering does not modify the ratio of signal to interference power in the time domain with the fact that, in the frequency domain, ...
Roger's user avatar
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1 vote
1 answer
170 views

FIR filter design for resampling

I am working on an audio resampler that is realized as a polyphase FIR filter. While testing, I found that it does not suppress aliasing as well as I would have expected. For testing, a sine sweep is ...
wolframw's user avatar
4 votes
1 answer
66 views

Ratio of aliased to desired energy of a sampled signal

In this article "Sampling: What Nyquist Didn't Say, and What to Do About It" from Wescott, the author shows in Figure 6, the plot of the frequency spectrum of a signal which goes through a ...
Link Coquin's user avatar
1 vote
0 answers
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Help figuring out how to extract audio content correctly from a file that produces spiky waveform with audible hiss/noise

I'm trying to extract PCM wave sequences from different files (files that are NOT audio files but contain audio data, and other data all in one file), and while this code does extract the expected ...
GDN9's user avatar
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1 vote
1 answer
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How does aliasing affect bits in an ADC?

I want to measure a signal whose frequency spectrum is infinite, but I am particularly interested in the frequency range $ 0 - 500 \ \text{Hz}$. I have a 12-bit ADC. The ADC has dynamic range $ 6 \ \...
Carl's user avatar
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1 vote
1 answer
148 views

Sampling a sinusoidal signal smaller than Nyquist rate

If we have a sinusoidal signal at 50 kHz and we sample it by an ADC with a sampling rate of 7 kHz. What would be the output of the ADC? Since the sampling rate is way less than the Nyquist rate (...
Jacob's user avatar
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Filter choice for the signal with the possible time jitter in sampling and frequency aliasing

I'm trying to filter data from the force sensor mounted on the end effector of the industrial robot arm. Mechanical vibration caused by the robot's motion (possibly by actuators, reductors, etc.) ...
Viktor Sokolov's user avatar
2 votes
1 answer
228 views

Can time aliasing cause peaks?

For the following I use the terms “time domain signal” and “frequency domain signal” as a Fourier Transform pair. The question is for generalized cases of continuous-time signals that once sampled in ...
Dan Boschen's user avatar
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Aliasing problem with pressure data

I have done some pressure measurements of flowing air with transducers that had a frequency response of 5 kHz. The data from these transducer was sampled also with 5 kHz and this is where my problem ...
Maxi 9000's user avatar
5 votes
2 answers
920 views

How to measure aliasing?

Aliasing is bad, and we want good filters when downsampling. While what qualifies as aliasing is well-defined mathematically, and we can manually design filters with various tradeoffs, how do we ...
OverLordGoldDragon's user avatar
5 votes
2 answers
553 views

How to avoid harmonic distortions in a DAC?

I have a DAC which is assumed to be nonlinear, such that it produces unwanted harmonic distortions at integer multiples of the input frequencies. (EDIT: Any other nonlinear distortions, such as ...
Harry's user avatar
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1 answer
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Difficulty Understanding a Triangular Graph: Aliasing of Signals

I have been reading a textbook on the "fundamentals" of signal processing but the author of the textbook has not given any explanation for the triangular graph located at the bottom of the ...
Sebastian Szymczyk's user avatar
12 votes
2 answers
1k views

Where are these aliasing artifacts coming from in transmitting audio? (Frequency reflection, duplication)

I am trying to understand how a SIM7600G 4G modem degrades the audio when configured for 8 kHz sampling rate. I created a reference audio using librosa.chirp to slowly sine sweep from 30 Hz to 3400 Hz....
Peter's user avatar
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proof of alias matlab sin wave and syntax for time array

I have been asked to prove the following; Show that a sinusoid of amplitude 10V and frequency 2kHz sampled at %fs = 10kHz is an alias of a 500Hz sampled signal. I have develped the code for the 500hz ...
Tam's user avatar
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0 answers
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Azimuth image extent in frequency domain SAR algorithms (RDA, omega-k)

When looking at the practical implementation of frequency domain SAR imaging algorithms like the range Doppler algorithm (RDA) and the omega-k algorithm (also called range migration algorithm, RMA) as ...
contiguousCentipede18's user avatar
2 votes
2 answers
188 views

Reconstruction of a Ricker Wavelet using inverse discrete fourier transform - signal cut in a half?

I am new here and new to DSP, so maybe my question is really basic. I have the formula for the Ricker wavelet (Mexican Hat) in frequency-domain and I wish to do an inverse Fourier transform to recover ...
Luis Fraga's user avatar
-1 votes
2 answers
96 views

Is square of signal more recoverable than signal itself?

Let $x[n]$ be aliased sampling of real-valued $x(t)$ over $t_0 \leq t \leq t_1$. Can $|x(t)|^2$ be recovered more accurately than $x(t)$, over $t_0 \leq t \leq t_1$? If so, how? For $|x[n]|^2$, ...
OverLordGoldDragon's user avatar
0 votes
1 answer
56 views

Sampling frequency to use with irregular signal

I have experimental data where I collected data points over time and my "signal" looks oscillatory in nature (y-axis values are more or less constrained in a y-axis bandwidth), but the curve ...
LobsterMan123's user avatar
1 vote
1 answer
243 views

Reconstructing an undersampled signal by cutting off at the signal's maximum frequency

Assume a (continuous) band-limited signal $f$, that is, a signal for which $F(s) = 0$ for all $\lvert s \rvert > p / 2$. If the signal is sampled with frequency $p$, we can reconstruct it by ...
Dan Oneață's user avatar
3 votes
0 answers
79 views

Strange signal processing: is this chaos or spectral aliasing?

In the context of DFT calculation, I would like you to explain me why I get this red curve: I work with a DFT simulator I built myself in Python. When I plot the output $y[t]$ with the impulsional ...
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1 vote
1 answer
92 views

Is my solution correct?

$\textbf{Question:}$ $y_a(t)$ is a rectangular waveform defined as: $$\ y_a(t) = \begin{cases} 2 &t \in [0,1/25)s\...
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1 vote
1 answer
112 views

How can I find $x_r(t)$ in this case?

$$x_a(t) = 10 + 4\cos(30\pi t +\frac\pi 3) - \sin(250\pi t + \frac 14) -3\cos(500t + \frac \pi4) $$ $\textbf{Question:}$ This signal is first sampled at a rate of $f_s = 100$ samples per second to ...
Ahsan Yousaf's user avatar
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6 votes
3 answers
2k views

Moving average before downsampling: effect on Nyquist frequency?

First the simple questions: Is there an effect on the Nyquist frequency when I apply a moving average filter on the raw data before I downsample? And what does this do to aliased frequencies? ...
W_vH's user avatar
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1 answer
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Intuition for how much ringing a particular filter will induce

I've seen figures in various books about the the tradeoff between aliasing and blurring when using a gaussian-like filter: the narrower it is, the more it cuts off low frequencies and thus blurs it, ...
multiscale's user avatar
2 votes
1 answer
251 views

Why 5Hz aliasing with LPF implemented

I have a simple signal chain with a differential sinusoid as the input. This passes through the first amp which converts the signal to a single ended signal. The next block is a 4 pole low pass ...
user1919542's user avatar
1 vote
1 answer
162 views

How do I estimate possible aliased frequencies in sampling limited measurements?

Say I've got some data made from measurements with a too infrequent sampling rate; I know for certain there is aliasing. What I'm interested in is figuring out what frequencies are likely present ...
Davey's user avatar
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12 votes
3 answers
970 views

Other end of Nyquist limit

Say I perform FFT on some data. If the underlying (measurement) sampling rate is not twice the highest frequency, I will almost assuredly get aliasing. This limit on sampling we call the Nyquist limit....
Davey's user avatar
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1 vote
1 answer
89 views

What will happen when we reverse an analysis/synthesis system?

Suppose that we have four filters $H_0(z), H_1(z), F_0(z),$ and $F_1(z)$ forming a classic perfect-reconstruction 2-channel filter bank: Will the perfect reconstruction still be achieved if we ...
WilliamW's user avatar
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0 answers
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Is the slow waveform an alias - and why don't we see other alias'es of different frequencies?

The following figures are data from sampling the DC bus of an inverter for a BLDC/PMSM drive running a speed-loop with FOC. The upper subplots are FFT's of the signal and the lower subplots are of the ...
drC1Ron's user avatar
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1 answer
194 views

Having Nyquist bin = aliasing?

Here I motivate the question by deriving FFT upsampling for $N \rightarrow 2N$ with even $N$. One might naively try xup = 2*ifft([xf[:N//2], zeros(N), xf[-N//2:]]), ...
OverLordGoldDragon's user avatar
0 votes
1 answer
128 views

Sampling and Aliasing

What is meant to be explained in the section between the 2nd paragraph and the folding section in the Sampling sinusoidal functions section shown in this link? Why is $Nf_0$ written in $f+Nf_0$ ...
bb0667's user avatar
  • 103
12 votes
5 answers
1k views

What is the frequency representation of nonuniform sampling?

Uniform sampling can be thought of as multiplication of a function $x(t)$ with a Dirac comb function: $$\text{III}_T(t) = \sum_{k=-\infty}^{\infty}\delta(t-kT)$$ Multiplication of $x(t)$ with $\text{...
Gillespie's user avatar
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4 votes
3 answers
724 views

Stanford EE 261 HW6 Q1 - Sampling below Nyquist Rate

The problem (taken from here) asks for possible sampling rates that will not cause aliasing in the following frequency spectrum: The range of possible values after some math is given as $B_2 < f_s ...
Abundance's user avatar
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1 vote
1 answer
133 views

Removing aliasing from recorded signal

I am recording a signal from a vibration sensor with a frequency response that stops at about 7kHz, but linear up to 1kHz. I am thus recording data from it using an Arduino at 2kHz, so that signals up ...
Daniel Godø-Dempsey's user avatar
0 votes
2 answers
75 views

Aliasing in continous-time signal

I have the following signal and it was plotted with a sampling frequency (Fs) of 5Khz and F0 was then varied for 0.5Khz, 2Khz, 3Khz, and 4.5Khz. I obtained aliasing when F0 = 2Khz and 3Khz only. ...
Justin's user avatar
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0 votes
1 answer
247 views

How to visualize frequency domain of signal with multiples of $f_s$?

Is it possible to visualize signal in frequency domain for frequencies bigger than $f_s$? I'd like to get the plot of some example signal like that: I tried to create some signals in ...
Curious's user avatar
  • 355
2 votes
1 answer
99 views

Noise from irregular sampling pattern

In this paper the author says By using an irregular sampling pattern and filtering the irregular samples to create the pixels, featureless noise is produced from such high frequencies rather than ...
a piece of something's user avatar
0 votes
1 answer
33 views

Running a signal through a circuit with some odd components

I am studying a course in signal analysis and systems. Currently we are looking at aliiasing, samplig,DTFT and reconstruction. I got stuck on an excercise. For the in signal $x_{a}(t)=2\cos(2\pi F_{0}...
Aedrha's user avatar
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-1 votes
2 answers
73 views

What should be my sampling frequency for a peak detector output where it is extremely important for me to capture the first time the peak occured?

Following is the output of the peak detector: The amplitude is not important to me, however the time when the peak occurs is extremely important. So my microcontroller will have an algorithm like ...
needbrainscratched's user avatar
5 votes
2 answers
279 views

Nyquist frequency isn't working

The situation is that I have a signal with linearly increasing frequency, $$\text{sin}(2\pi\omega(t)t),$$ where $\omega(t)=a+bt$ for some $a$ and $b$, and we constantly sample at one point per second ...
CoolMathsGuy's user avatar
0 votes
1 answer
678 views

Resampling pitch shifter

I’m trying to build a very basic resampling pitch shifter which reads samples from disk. I only want to change -+6 semitones without keeping the original sample length. I already have all the classes ...
David912's user avatar
  • 103
1 vote
1 answer
291 views

How is sampling affecting this sine wave?

I am trying to create a sine wave in python, but when I graph it, it looks like this: here is the code I used to make the signal: ...
user57935's user avatar
2 votes
1 answer
1k views

Aliasing in Doppler Radar

my book about RADAR says that: If a Continuous wave radar sends a sine wave at frequency $f_T$ to a moving object (at speed V), a frequency $f_R$ is received. Their difference is called Doppler ...
Kinka-Byo's user avatar
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0 votes
1 answer
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Digital lowpass filter causing aliasing

I'm writing a biquad filter program in C++, using the RBJ Cookbook as the source for the formulas. https://www.w3.org/TR/audio-eq-cookbook/ The lowpass filter that I've made seems to half work. The ...
Dominique Kapiamba's user avatar
1 vote
1 answer
83 views

How to verify and plot expression for sampled signal is correct?

Given the signal $x_a(t)=4cos(2\pi\times40t+\pi/3)+10cos(2\pi\times160t-\pi/6)$, I am to sample it at $f_s=200Hz$ and find the expression for $x[n]$ My process: $$x[n]=x_a(nT)=x_a({n\over f_s})=4cos(0....
Kevin KZ's user avatar
0 votes
1 answer
91 views

Aliasing Issues in Sub Band Coding

The general structure of Sub-Band Coding (SBC) is shown below: The diagram shows that after each of the analysis filters, decimation is performed by a factor M which corresponds to the number of ...
malik12's user avatar
  • 488