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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54 views

Every second sample noisy

I sampled a signal and unfortunately every second sample is very noisy. The noise is Gaussian and bandlimited exactly in the same bandwidth as my signal. Is there a way to improve the noise without ...
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Apply timeshift to undersampled signal after bandpass after sampling?

I have sampled my continuous signal $x(t)$ at $x[n]=x(n/f_{\rm samp})$. The signal is undersampled, and I know I will not be able to recover my original signal anymore. After sampling a bandpass is ...
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Magnitude spectrum for discrete-time signals

I am doing the following question (it is not homework, I am preparing for an exam). The time discrete signals $x_1(n)$ and $x_2(n)$ is created by sampling the continuous signal $x_a(t) = \cos (2 \...
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What's wrong with my minBLEP Hard Sync Sawtooth code?

I implemented a Sawtooth Oscillator which uses minBLEP - Eli Brandt's original paper The minBLEP approach works very well for a normal Sawtooth but I specifically want to implement Hard Sync and ...
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152 views

Samples of period to frequency, sampling theorem

In the sample rate of 96kHz there are 96000 samples in a second. So a periodic waveform with period 96000 samples has a frequency of 1Hz. A signal with period of 9 samples is ~ 10666 Hz. Of 5 ...
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Aliasing after downsampling [duplicate]

Let me start with time domain representation of the original signal \begin{equation} x_n=\sum_{k=0}^{2N-1}X_ke^{j\frac{2\pi nk}{2N}} \end{equation} where $2N$ is number of time/frequency samples ...
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1answer
50 views

Help with a product of a sum of infinite series [closed]

i would like some help with this: given: $$ h[n]=2^{-n} u[n] $$ calculate the series: $$ \sum_{r=- \infty }^ \infty h[n+4r] $$
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1answer
361 views

unexplainable aliases in spectrogram

My scope has 200 MHz bandwidth and can sample at 4GS/s I'm sampling a 138 MHz RF signal at 500 M Sa/s storing 14 M points. When I plot the spectogram in matlab I get the following spectrogram(Data,...
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358 views

Aliasing Square Wave

I'm having a really weird issue with generating waveforms from frequencies C1 to C8. When I generate sine waves, everything sounds good; no problems whatsoever. However, when I generate a square ...
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1answer
127 views

A question about sampling theory

Let`s say I have a signal $m(t)=\cos(4\pi t) + \cos(6\pi t)$ so we can say the signal is containing frequencies $f_1= 2\mathrm{Hz}$ and $f_2= 3\mathrm{Hz}$. The cut-off frequency of the low pass ...
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352 views

Is this a kind of aliasing error and how to make correction?

I use a Discrete Fourier Transform to have a representation in the frequency domain: Notice that, both the real and the imaginary line are softly reaching zero on the left, from 0.5 Hz to 0 Hz. This ...
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146 views

Are time series data always contain noise?

I wonder if every time series data should contain noise or not. For example I am taking the price of a ticker, say Yahoo, every hour and noting the values. Does this data contains noise or not?
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1answer
464 views

How to ensure anti-aliasing in image resampling at lower resolution?

Suppose I have a 1D image with intensities $f_i$, $i=[0,n-1]$, where $n$ is the number of pixels. I want to downsample it to have $\frac{n}{2}$ pixels (let $n$ be an even number). For each new point I ...
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4k views

Why is a square wave aliased?

I understand an ideal analog square wave contains sine-wave-components above Nyquist frequency (and towards infinity) and is thus subject to aliasing. So obviously we need an anti-aliasing-filter. Or ...
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Apparent frequency due to aliasing - proof [duplicate]

I know that If we are trying to sample frequencies above the Nyquist frequency, aliasing will occur, and the apparent frequency we get is given by: $f_{alias}(N) = |f-Nf_{s}|$ where $f$ is the ...
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Does sampling in the frequency domain cause time-domain aliasing?

Let's say I have an impulse response $h[n]$. I analyze the power spectrum of that impulse response similar to fourier transformed $h[n]$ corresponding to roughly $H[f]$. Now I compare $H[f]$ with ...
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425 views

how to correct minBLEP sawtooth oscillator DC bias

In my implementation of minBLEP, overlapping minBLEPs result in a DC bias as the frequency increases. This is because each minBLEP correction (i.e. the minBLEP minus the aliased step) has a DC bias. ...
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591 views

What does it mean for a signal to alias to another?

I know the definition of this is simple and I do understand the concept of aliasing (I think) in the way that multiple signals can be aliases of each other. For example, I get it when some one says: ...
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I still get aliasing of my signal, even though I stay below the Nyquist frequency. What am I missing?

Thanks in advance for any help with my newbie question. I've been consulting quite a large number of resources in order to understand how I can create and playback a nice sawtooth without aliasing, ...
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1answer
4k views

Sampling of band-limited white noise

The context is communication where we have a front-end that samples a signal and a noise (but here we focus only on the noise). My goal is to determine the noise power that I should use to simulate (...
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2answers
282 views

Can aliasing happen in Laplacian Pyramids?

I want to use the Laplacian pyramid framework for representing images. The The Laplacian Pyramid as a Compact Image Code's language seems to provide freedom in the choice of blurring/interpolation ...
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3answers
957 views

Reflecting negative frequency to positive frequency

I am trying to synthesize sinusoids by using window function in the frequency domain. It involves: In frequency domain, shift the window to center around the peak frequency To generate a DFT frame, ...
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1answer
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Aliasing of a Signal

I am really confused about this exam question regarding Aliasing. I have a signal of 2Hz, which I needed to draw a square wave of, over a period of 8 seconds. It Then asks, "Starting from the ...
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1answer
73 views

100 kHz sinewave contaminating a signal sampled at 48 kHz

If sampling at a rate of 48 kHz, with no anti-aliasing filter on the input, and the input signal is contaminated by a 100 kHz sine, at what frequency would the sinewave signal appear in the output ...
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Does MSAA make sense in audio / 1d data streams?

In graphics, MSAA is a technique where you take multiple samples of something per pixel and then average the values to get the final pixel value. The image quality improves as a result, and its ...
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Exact formula for alias of Discrete Fourier transform for periodic sigals

Suppose that $f(t): \mathbb{R} \to \mathbb{C}$ is a $T$-periodic signal, with highest frequency $f_h$. Now suppose that our sampling rate frequency is lower than $f_h$, and is not any multiples of $1/...
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aliasing to a 50 Hz sine wave sampled at 5000 Hz sampling rate?

I sampled a 50Hz sine wave (its not perfectly a sine wave, it's a data coming from current sensor using Arduino). Using real time graphing technique by sending the data from Arduino to the PC I ...
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Can sample aliasing of strictly white noise lead to random walk (drift) in the sampled signal?

Aliasing of tones higher than the Nyquist frequency, and where the tone may have some degree of nonlinear distortion can appear as low frequency 'drift' or even near static bias in the sampled signal. ...
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1answer
143 views

How does sampling and subsequent resampling affect aliased harmonics?

If I sample a signal with a harmonic higher than half my sample frequency I can predict the aliased frequency easily as $$|F_h-kF_s|$$ But what if after sampling the signal, I re-sample at a lower ...
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What is the proof of the equation for the aliased frequency fa = |R*n - fs|?

R (sampling rate) fs (signal being sampled fN (the Nyquist frequency) fa (aliased frequency) I was hoping someone could explain to me why this is true with a more mathematical proof. it seems ...
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Soft question: Why do we need to reconstruct a signal?

I am currently reviewing the Nyquist criterion which says I need to sample the signal at 2 times the maximum frequency in order to avoid aliasing in the reconstructed signal. My question is that in ...
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1answer
643 views

Illustration of time domain aliasing cancellation (TDAC, MDCT, lapped transform)

Can someone find or make a visual illustration of how time domain aliasing cancellation works in lapped transforms such as the MDCT? I think a graphic would make it a lot easier to understand, and I ...
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680 views

How can I enforce aliasing with Audacity?

I would like to hear how aliasing sounds like. How can I get this with Audacity? (I was told that I should adjust the Fourier coefficients in Audacity. I have no idea where I can do so / how I should ...
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691 views

why Sampling with higher than nyquist frequency is causing aliasing?

fm=20000 and I am sampling following signal at 65000 Hz: ...
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1answer
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How does the number of frequency-domain sampling points influence the outcome of an inverse FFT?

Given some frequency-domain representation of an impulse response. How does the number of frequency-domain sampling points influence the outcome of an inverse FFT, if I keep the sampling frequency ...
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1answer
143 views

Designing the filtering for a time domain data acquisition application

I want to filter sensor signals for a data acquisition application on an ATmega microcontroller. The interesting parts of the signal are in the range 0-5Hz, and I'd like to leave these mostly ...
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3answers
4k views

Visualizing aliasing in Matlab

I am trying to verify for myself that aliasing actually makes it impossible to distinguish the "real" and the aliased frequency. What I have done it set the sampling rate to 20 Hz and created two sine ...
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1answer
117 views

What does “two signals aliasing to each other” mean?

So I just read something that two signals are aliasing to each other. I know what a single signal is being aliased - that is when sampling rate is not higher than or equal to the Nyquist rate. But I ...
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728 views

Spectral images - How do they appear during ADC?

Why is it that spectral images appear? I know they appear for $F_s$, but why those replicas appear, I don't know. E.g., sampling $x(t) = sin(1000 * 2\pi t)$ with a sample frequency of 230 Hz. I know ...
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164 views

Generating a sound where end frequency is 1/2 of the start frequency

I am very very new to signals, and I am trying to generate sounds based on some parameters from a database. So, the database stores the following: startFrequency endFrequency startAmplitude ...
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1answer
290 views

Which antialiasing filter before equispaced sampling

I am using MIT-BIH arrhythmical database where I have a digital signal of 1200 Hz so 1200 samples per second. This means that analog filters have already applied to remove the frequencies over Nyquist ...
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2answers
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Create an aliased image in FD

Is there an accurate way to create an aliased image from the Fourier transform of the original image? in other words, i have the Fourier coefficients of an image and i want to make down-sample in ...
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1answer
494 views

Simple analog anti aliasing filter good enough if signal frequency is far from sampling frequency ? What about equivalent time sampling?

I have one and only one frequency signal, a sine signal at f = 10 kHz that is sampled at Fs = 320 kHz. I have read about applying a simple analog anti aliasing (AAA) filter then oversample, do some ...
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Aliasing beating frequency

As I understand aliasing is because you sample a high frequency with a low sample rate, and the sample points don't have enough information about the high frequency component. Here is an example of ...
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1answer
905 views

FFT and aliasing

I have got a txt file which contains voltage and time data. When I did fourier transform using fft function in matlab I got complex numbers. I understand that the real part is the magnitude and the ...
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How to predict the spectrum of an aliased/folded signal without looking at the FFT?

This seems like a trivial concept but I just can't get the hold of it. I have a signal with two complex sinusoids having frequencies -25MHz and 17MHz. Currently it is being sampled at 64MHz so I get ...
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reduce harmonics produced by microcontroller

I'm generating an 18kHz sine signal using a dsPIC microcontroller at 44100kHz (I'm not sure I can call it sampling rate, maybe generation rate, although the concept is the same). The dsPIC's DAC then ...
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Increasing Image Resolution

I know of some oscilloscopes (DSA8300) that repeatedly sample at a few hundred kS/s to reconstruct a few GHz signal. I was wondering if this could be extended to 2D signals (photographs). Can I take a ...
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1answer
506 views

Using Spectrogram to check whether aliasing will occur

I was wondering if the spectrogram can be used as a MATLAB tool to check whether or not aliasing will occur when the signal is downsampled from let's say, 44.1kHz to 8kHz? And if yes, how do I go ...
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Is there such a thing as band-limited non-linear distortion?

So if you generate a square wave by just switching a signal between two values, at sample boundaries, it produces an infinite series of harmonics, which alias and produce tones below your fundamental, ...