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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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 ...
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28k views

Alias frequency Formula

I'm taking a multimedia systems class in my MSc Computer Science, and I'm having some trouble understanding the formula for the alias frequency - this could stem from my misunderstanding of the alias ...
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1answer
312 views

IQ Sampling and Oversampling Differences? *Confused*

Two different thought process that produce two different alias band calculations .... What concepts are these? If I have two 1 GHz ADC's and they sample with 90 degree offset (A comment said this is ...
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113 views

What does the frequency band mean when it comes to finding aliases?

The time signal which i'm trying to find the aliases for is: $$x:{\mathbb R}\rightarrow {\mathbb R}\\\ x(t)=\cos(50t) +2\cos(70t).$$ If the sample period is $T_s = \frac{\pi}{60}$ then according ...
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44 views

Digital lowpass filter causing aliasing

I'm writing a biquad filter program in C++, using the LBJ Cookbook as the source for the formulas. https://webaudio.github.io/Audio-EQ-Cookbook/audio-eq-cookbook.html The lowpass filter that I've made ...
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37 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....
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119 views

Aliasing below $f_s/2$

phi = exp(linspace(0, log(511), 1024)) - 1 x = cos(2 * pi * phi) Above will alias, despite peak instantaneous frequency evaluating to ...
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1answer
146 views

Band limited discrete signals division

If I take two analog, band limited signals $ x(t) $ and $ y(t) $ with non-zero $y(t)$ I can define the division: $$ z(t) = \frac{x(t)}{y(t)} $$ In general $z(t)$ may have a very wide bandwidth, also ...
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26 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 ...
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1answer
117 views

Sample-rate, filtering, digital-filtering and aliasing

I am strugling with a question that I hope someone can help me with. I am recording single molecule events which I detect is picoampere square deflections. I wish to use as gentle low-pass bessel ...
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1answer
116 views

Is spectral density conserved after aliasing?

Will the integral of the PSD of a down-sampled signal still equal the variance in all cases
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1answer
466 views

Choosing a Sampling Rate and a Cutoff frequency

I have an assignment: You wish to generate a pure 1000 Hz tone digitally using a computer. How would you choose a sample rate that assures that you could generate the tone and use the same sample ...
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93 views

Condition for aliasing

Which one of the following is the condition of aliasing? (a) Tails of the replicas enter into the Nyquist interval (b) The tails of the replicas enter into the Nyquist interval and add to the ...
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73 views

Question about aliasing

As far as I understand, you can have two different continuous-time signals with the same discrete-time frequency spectrum after they are sampled and it may be possible these shifted replicas in the ...
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1answer
88 views

Multiple choice on sampling and aliasing

I found some multiple choices in a well known book . The problem is that I don't get the answers in some and I want to do so. Question 1: The signal x(t) with Fourier transform $X(j\omega) = u(\omega)-...
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52 views

Prefiltering to Avoid Aliasing

In processing analog signals using discrete-time systems, it is generally desirable to minimize the sampling rate. This is because the amount of arithmetic processing required to implement the system ...
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1answer
148 views

Difference in information between IQ Sampling vs. Real Sampling at $2F_s$

As per my current understanding we use IQ sampling as way to increase the useful bandwidth to Fs rather than $F_s/2$ when viewing the FFT because the IQ sampling removes the negative frequencies and ...
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68 views

Sampling pure tone sine waves [closed]

What would happen if I am using the maximum frequency as the sample rate for sampling a pure tone sine wave? For example, a $10\ \rm kHz$ sampling frequency for a $10\ \rm kHz$ monotone sine wave. ...
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How to prevent (or remove) aliasing when a cross-correlation between spectra is performed

This is my problem: I'm implementing a tool which cross-correlates a spectrum (fluxes as function of wavelength, obtained directly from an instrument) with a template (fluxes as function of wavelength,...
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306 views

What can be meant by “bandlimited”?

This question was a source of disagreement on whether "amplitude aliasing" can occur for a signal bandlimited to below half the sampling frequency. The question was closed before the ...
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126 views

Aliasing at $f_0 + kf_s$

In this question, it has been proved that $x(t) = \sin(2\pi f_0 t)$ and $x_k(t) = \sin(2\pi (f_0 + k f_s) t)$ have the same sample points. So sinusoids with frequencies $f_0$ and $f_0 + kf_s$ will ...
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428 views

How to prevent distortion after down-sampling?

I am new to audio signal processing, but in one of my machine learning projects that I am working on, I need to down-sample my audio somewhere in the middle of my neural network. Therefore, I need a ...
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1answer
377 views

Generating digitized white noise: uniform vs normal sampling

Consider the following two ways of generating noise in the time domain for audio applications: Generate samples from a uniform distribution [-amplitude, +amplitude]...
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3answers
76 views

Sampling a low-frequency sound doesn't work at some sampling rates

When sampling a low-frequency sound (like a 55Hz sine wave) I hear an additional high frequency sound at certain sampling rates, but not at others. This happens in Audacity and in my own program. For ...
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1answer
67 views

Sine Wave “Lobes” (Basics, and probably a dumb question)

I am beginning my journey on trying to understand a little deeper on signal processing. I wonder if the effect I am seeing is worth any spit or is there a deeper level of understanding is apparent I ...
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30 views

Find the frequencies present when a non-sinusoidal wave is reconstructed

A 1.6kHz periodic (not sinusoidal) signal contains all its harmonics, both even and odd. The signal is sampled at 3.6kHz and ideally reconstructed. What frequencies are present in the output? I know ...
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37 views

Why should wavelet re-synthesis produce an output when the main component is suppressed and what does this mean for denoising?

I understand that aliasing occurs in DWPT if the wavelet used is of low order since the "filters" are not perfect and the combination of down sampling and overlapping between bands causes ...
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120 views

PolyBLEP: solving two part residual

The Polynomial Bandlimited Step (PolyBLEP) methodology involves approximating the sinc() function with a polynomial. The most basic polynomial to choose is a uni-polar triangular pulse as it is the ...
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3answers
227 views

aliasing in image processing

I know that aliasing occurs when a signal is subsampled. If the sampling rate is lower than twice the max frequency in a signal, aliasing occurs. How is it in pictures? as far as I know, a sinc-filter ...
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708 views

Decimation Question about using a low pass filter before downsampling

I have a bunch of audio files that have a sample rate of 380kHz, however I would like to reduce this sampling rate to 44.1kHz. From doing some research online, it seems like I will have to use a low ...
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29 views

synchronize adcs with neuronal network

if i have two adcs(analog to digital converters) sampling a signal. Is it possible to synchronize the two adcs with deep learning? as far as i know, with super-resolution on image processing it is the ...
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76 views

Direct Digital Frequency Synthesis, NCO and negative frequencies

I need to translate a frequency band generated by a DDFS designed in a FPGA (using Xilinx DDS Compiler). My output to the NCO is in I/Q format. I chose to use a NCO to perform the frequency shift but ...
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Partially aliasing in Signals

I have read a paper about super resolution where signals are used that are partially aliased. here the paper If the sampling rate is smaller than the 2*max frequency but greater the max frequency, ...
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1answer
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What is an example of using aliasing to your advantage when recovering an input signal?

Suppose you have an arbitrary analog input signal $x_a(t)$ guaranteed to have frequencies within a bandwidth $[f_1,f_2]$ Hz. Suppose your sampling frequency $F_s$Hz, and sample $x_a(t)$ to produce $...
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42 views

Multichannel sampling with aliasing

if i have 2 sensors, sensor1 and sensor2, that sample a signal on complementary points so that sensor2 samples always between sensor1s sampling points. can I achieve the doubled sampling rate with the ...
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3answers
70 views

Loosing information in decimation - without aliasing

We sample each other sample (01010101). Now say we have a signal - that is inside the original sample which has the pattern of (010-1). Decimation gives us 000 for this sub-signal. How to prove this ...
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3answers
244 views

How do you sub-sample an FFT?

I'm currently trying to understand this paper on a Sparse Fourier Transform. On page four, there is a section on a sub-sampled FFT. The purpose of this section is to show that you can compute a sub-...
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409 views

Accelerometer BMI160 changing bias

Goal: Obtain the 3-axis accelerations from the Bosch BMI160 IMU when measuring the accelerations of the bogie of a commercial train. The accelerometer used is installed in a PCB and used by an mbed ...
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2answers
104 views

Nyquist Theorem adding two same frequency near to Nyquist Frequency with phase shift

This is my first question on this platform. Sorry if I made mistakes. What happens if we add two or more same frequency signals near to Nyquist Frequency with phase shift and sample them? For ...
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346 views

aliasing folding phenomena in frequency domain matlab

Hello i am trying to create the folding phenomena of undersampling in matlab, When i undersample the sampling frequency is 135 less than the Nyquist frequency for 70 Hz signal ou will see that it is ...
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2answers
84 views

Measuring Phase Difference at DC bin aliased frequency using FFT

I have a code in which two complex signals (I/Q) are created having same frequency but with phase difference. FFT of both signals is taken and atan2 is used to compute phase after which the difference ...
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734 views

How do Anti-Aliasing Filters filter the signal?

I have programmed a anti-aliasing filter that uses the fourier-transformation and makes a perfect cutoff on my desired cutoff frequency for downsampling without aliasing. I have read about other ...
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1answer
76 views

Super resolution with aliased signal

SKIP to Questions below if you want : In super resolution I can create a high resolution signal from a low resolution signal. But it is also possible that the low resolution signal contains aliasing. ...
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1answer
122 views

How to find correlation between two signals regarding peaks?

In a super-resolution task, I try to predict the higher frequencies of a signal. X low-resolution (lr) is my input and Y high-resolution (hr) is the target. Where X contains only frequencies till 2 ...
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3answers
75 views

does aliasing occur always if i sample a vibration in real world applications?

I was reading about the aliasing effect and nyquist. I understand that aliasing effect occurs if the sampling rate is lower than twice the maximum frequency in the signal I want to sample. So I was ...
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268 views

Why is the digital frequency highest at $\pi$ and what does it mean in terms of analog frequency? [duplicate]

I can't seem to comprehend why the digital frequency is highest at $\pi$. I know the relationship between the digital and analog frequency is given by: $$\omega = 2\pi\frac{F}{F_s}=2\pi f$$ Where $F$ ...
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109 views

Can the (point-wise) multiplication of two discrete band-limited functions be inherently aliased?

I'm not fully used to the language of DSP, so forgive me if I confuse some of the notation, or if the below is trivial. I'm interested in the case where we want to do the point-wise multiplication ...
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2answers
2k views

Circular Convolution of Length L of Sequences of Length Greater Than L

I'm trying to understand how may I obtain the circular convolution of length L when the sequences I'm trying to convolve are of length greater than L. For instance this Matlab code using sequences ...
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2answers
212 views

What is the right way to downsample using Fourier method?

I want to know what is the right way to downsample a sampled signal using Fourier transform as the implementation in scipy.signal.resample confuses me. Reading ...
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260 views

Digital to analog aliasing or mirror query… DAC can output negative frequency?

Using a clock Fs = 1 MHz. The Digital to Analog (DAC) can make frequencies upto 500 KHz. 500 kHz to 1 MHz is an alias? Or is it called a mirror?? Is aliasing a concept only on the ADC and sampling ...