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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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28 views

Where should I set my anti-aliasing filter corner frequency for this signal?

I have a Fourier transform of an arbitrary digital signal. The transform has For 1024 frequency bins. The magnitude plot of the first 100 is below, with no surprises in the unplotted 924 bins. Now, ...
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1answer
22 views

Values of angular frequency of discrete-time sinusoidal signal

Why are the values of angular frequency of discrete-time sinusoidal signals in between -pi and pi?
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1answer
56 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
59 views

Why does my sinusoid look “AM” in shape?

My code is : Fs=200e6; Ts=1/Fs; NFFT=2^14; Runtime=(NFFT-1)*Ts; t=0:Ts:Runtime; f_in=90*1e6; y_in=sin(2*pi *f_in *t); plot(t,y_in) ylim([-1.5 1.5]) Then why does ...
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1answer
27 views

Aliasing correspondance with respect to DFT

Given a sampling frequency Fs lets say we plot the magnitude of the fft of a temporal signal $x$, for different frequencies above the Nyquist frequency, to show the effect of aliasing: ...
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1answer
47 views

Better understanding of downsampling (decimation) and upsampling (interpolation)

Although some questions were asked about this topic, I have not seen any that answers all the basic questions, that is why I took the liberty to ask more about this. I suggest to limit, (or at lest ...
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2answers
65 views

Is spectral leakage normal for FFT?

I record a sample of 2000 data points, with a sampling rate of 40khz, so freq. resolution is 20hz. I multiplied the chunk of data with a Hanning window prior to doing the FFT. I recorded a 1khz test ...
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0answers
44 views

Aliased Signal's Frequency

So I have an incoming signal of 137.9 MHz and a sampling frequency of 1.4 MHz. Once sampled how do I calculate the aliased ...
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1answer
58 views

Sampling Audio Signal [closed]

I generate a 19kHz audio signal with sampling frequency of 44100 using Matlab. Due to the sampling, some other frequencies are generated in addition to the 19 kHz signal. When I play this audio, I ...
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1answer
43 views

Calculate aliasing of $x_a(t) = \cos{(2\pi300t)} + \cos(2\pi600t)$ when sampled with $F_s = 1000$

I'm asked to sample the signal $$x_a(t) = \cos{(2\pi300t)} + \cos(2\pi600t)$$ with sampling frequency $F_s = 1000$ and plot the magnitude spectrum for the resulting sampled signal. My thinking is ...
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75 views

Aliasing from downsampling and Nyquist

In a book Conceptual Wavelets in Digital Signal Processing by Lee Fugal 2009 on page 246 the author talks about aliasing present in DWT subbands due to downsampling by 2 and states: Recall from DSP ...
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1answer
93 views

Understading sampling theorem and aliasing

A real-valued analog signal with a flat spectrum between f = 0 Hz, and fmax is sampled at a sampling frequency fs = 24 kHz. The sampled signal is then processed with an ideal lowpass filter with ...
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1answer
56 views

Amplitude Response at greater than half the sampling frequency

I am hoping to clear up some confusion I have. In a lab I am taking, we analyzed the amplitude response of a simple system. We found that as we increased the input signal frequency to greater than ...
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37 views

Minimum sample frequency that allows reconstruction of information signal but VIOLATES Nyquist?

Say in the frequency spectrum, you have an information signal between (-100, 100) Hz, and a noise signal between (-700, -500) and between (500, 700) Hz. What is the minimum possible sample frequency ...
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1answer
67 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
57 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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1answer
126 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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1answer
58 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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1answer
374 views

Downsampling impact on complex phase

For my application, I have to downsample a bandpass complex signal which spectrum is located on the second Nyquist zone. Knowing that this processing will cause a spectrum inversion, what would be ...
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2answers
269 views

Alias-free digital nonlinear filter design

@Jazzmaniac has a good answer to the question of how to design an alias-free digital nonlinear time-invariant filter here: https://dsp.stackexchange.com/a/28787/18276 Basically, according to that ...
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0answers
151 views

Decimation Aliasing

Lets say you have a signal which is sampled at rate $f_s$ and the bandwidth after sampling is $B$. Now you want to decimate this signal with a new sample rate $f_{s, new}$ where $f_{s, new} < f_s$ ...
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1answer
101 views

Designing an experiment to show blue noise not adding noise below nyquist and not aliasing above

I read this paper from 1983 "Spectral Consequences of Photoreceptor Sampling in the Rhesus Retina". This paper talks about blue noise sampling patterns in the retina and says that: The results (...
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2answers
280 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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1answer
83 views

What does it mean that the DFT equals the Complex Fourier Coefficients for even frequencies?

I have a periodic signal, with period $1$ $$x(t) = \begin{cases} 1 \qquad & 0 \le t - \lfloor t \rfloor < \tfrac12 \\ 0 \qquad & \tfrac12 \le t - \lfloor t \rfloor < 1 \\ \end{cases}$$ ...
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3answers
125 views

Frequency of a single sample in a digital signal and aliasing

I'm involved with digital audio synthesis. I know that if I create a raw non band-limited waveform it would contain frequencies above Nyquist thus violating the Nyquist Shannon theorem and the signal ...
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1answer
73 views

What happens if an harmonic in a band-limited signal at Nyquist frequency is added to a 90 degrees out-of-phase replica of it?

I'm interested about aliasing in digital audio and I wonder if aliasing can be produced by simple mixing of band-limited signals. As I know a band limited signal can contain frequencies up to sample ...
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317 views

Can addition of two band limited signals create aliasing?

Can mixing/adding two band-limited signals create any frequencies above Nyquist?
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1answer
56 views

low frequency transform

I was wondering which type of signals have bounded-support Fourier transform. e.g. their transform is limited from zero to some non-infinite frequency. The main reason I'm into it is that in Shannon'...
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2answers
60 views

Determine minimum sample rate for continuous sinusoid

Consider a signal $$ x(t) = \cos(175\pi t) $$ which is sampled to produce discrete time signal $$ x[n] = x(nT_s) $$ The fundamental period of $x[n]$ is $$ N_0 = 7 $$ Given this, what is the smallest ...
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1answer
162 views

What happens on signal during aliasing?

So I have signal with frequency of $15Hz$ and sample rate frequency is $20Hz$. What happens if we sample the signal at a frequency that is lower that the Nyquist rate? We will have aliasing. Sample ...
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0answers
57 views

Band Limited Impulse Train - DC offset correction

I am trying to get band limited saw-tooth wave. I have found this paper: Alias-Free Digital Synthesis of Classic Analog Waveforms. I am prototyping this code in common LISP, here is snippet of what I ...
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1answer
212 views

Understanding the mathematical proof for the alias frequencies in a sampled sine wave

I'm struggling to get my head round the mathematical proof for the alias frequencies in a sampled sine wave. I understand that sampling a sine wave of frequency $f_0$ every $t_s$ seconds gives you: $...
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1answer
84 views

Avoid Aliasing when filming a moving car

I want to film a moving car with a rolling circumference: 190,5 cm and wheel circumference: 60 cm and 5 spokes. I record with 24Hz. What can be the maximal speed of the car to avoid aliasing?
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2answers
1k 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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1answer
356 views

Aliasing due to the Convolution of Gaussian Functions

For two discrete-time sequences $f[n]$ and $g[n]$, their linear convolution $(f*g)[n]$ is also given by $$f*g = \mathcal{F}^{-1}(\mathcal{F}(f) \cdot \mathcal{F}(g)),$$ where $\mathcal{F}$ and $\...
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1answer
368 views

Aliasing in digital communication system

In a digital communication system, is it possible to counteract the aliasing problem by properly tuning the constellation order $M$ and/or the carrier frequency? Here is my train of thought, please ...
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2answers
92 views

What does it mean that one frequency aliases another?

So I was watching a video on sampling and the professor asked which frequencies will alias to 0 and which to $B$ if we are sampling at frequency $f_{s1}$. What does mean that two frequencies alias ...
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1answer
74 views

How does the earphone cable in a mobile phone pick up the FM reception?

As I understand, the RF frequency-modulated signal centered in the range of $88-108\textrm{ MHz}$, is picked by the earphone antenna and is directly sampled by the sound card adc at $48\textrm{ kHz}$ ...
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3answers
601 views

Applying Nyquist theorem to digital vs. analog audio quality

I had a recent conversation with a friend about analog vs. digital recordings. He shared his opinion that music recorded by analog techniques is of superior sound quality to music recorded by digital ...
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2answers
169 views

Aliasing in audio

Reading wikipedia to be sure and it says: In signal processing and related disciplines, aliasing is an effect that causes different signals to become indistinguishable (or aliases of one another) ...
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3answers
390 views

Effect of aliasing when sampling at higher rate

Considering a signal $f(t)=\sin(2\pi t)$ with frequency $10\textrm{ Hz}$: Middle and bottom plots show the results of sampling at different rates. I'm trying to understand the case shown at the ...
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3answers
2k views

Upsampling - What purpose does the interpolation filter have?

I want to apply some nonlinear processing to a signal, namely: I want to implement a tube emulation which adds warmth/harmonic distortion to a digital audio signal. I am worried about aliasing, so I ...
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2answers
3k views

frequency folding due to aliasing in FFT

I am having problem understanding why negative frequencies are showing up to the right of positive frequencies in discrete complex FFT. I am not sure how to apply aliasing concept to explain such ...
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1answer
331 views

How much can we downsample by? and how much can we upsample by?

e.g. let's say we have a signal with B = 100 Hz that is sampled at 400 Hz. The anti-aliasing filter will remove replicas, and there is nothing to alias, and we downsample. If we downsample by 2, we ...
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2answers
872 views

Why is aliasing inherently non-linear?

E.g. when having 2 signals $x(t)$ and $y(t)$ and transforming each one with adding their spectra, the operation is linear, as the result would be the same as the transformation of $(x + y)(t)$. Even ...
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1answer
1k views

Why does this Moiré pattern look like this?

I was making some gifs of Mobius transformations in Matlab, and some strange patterns began to appear. I'm not sure if a deeper knowledge of the filetype/algorithm is needed to understand this ...
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1answer
409 views

Sampling and the creation of multiple images at integer multiples of the sampling frequency

From what I thought I learned about sampling is that when you draw a sampled signal in the frequency domain, you can show copies or "images" of that signal at integer multiples of the sampling ...
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1answer
134 views

Does $H(-z)$ produce aliasing? [closed]

Given $H(z)$ is the z-transform of a signal, I know that $H(-z)$ results in shifting of frequencies in DTFT by $\pi$ or $-\pi$. Does it produce aliasing ? How ?
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103 views

Can picking an inappropriate roll-off frequency for a digital filter just alias the roll-off value?

I believe a related question is asked here, but my question deals more with what filter is realized if one fails to consider design parameters relative to sampling rate. In designing an IIR filter we ...
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123 views

How to Sample Smooth Random Walks of Instantaneous Frequency

I want to generate a random sequence for instantaneous frequency with as little aliasing as possible (i.e I expect to see as close to constant amplitude as possible, with only the frequency varying). ...