# Tag Info

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

To perhaps help future readers, here is a graphical explanation of the two behaviors seen: harmonic distortion and aliasing / frequency fold-over: Harmonic distortion can result from any kind of non-...
• 703
Accepted

### Why does this Moiré pattern look like this?

You'll need to understand the sampling theorem. In short, each signal has what we call a spectrum¹, which is the Fourier transform of the signal as it comes in time domain (if it is a time signal), or ...
• 30.7k
Accepted

### Other end of Nyquist limit

Can't capture high $f$: insufficient sampling rate. Can't capture low $f$: insufficient observation interval. The DFT is a machine that spits out frequency measures, done by correlating against ...
• 8,913
Accepted

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

This behavior is likely caused by clipping (as nicely illustrated by @OverLordGoldDragon in the comments). Where exactly clipping is occuring is harder to tell, but a simple remedy is to lower the ...
• 15.3k
Accepted

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

The reason is that if it is true for any $m$, it is also true for $m=kn$. I will sketch the proof in another way. Call $f_s = 1/t_s$ sampling frequency where $t_s$ is sampling period, the two signal ...
• 6,595
Accepted

### What is the frequency representation of nonuniform sampling?

You might be interested in this particular reference paper: Digital Spectra Of Non-Uniformly Sampled Signals : Theories and Applications is a somewhat obscure reference (from 1988! can't go wrong!) ...
• 6,055
Accepted

### Moving average before downsampling: effect on Nyquist frequency?

There is no effect on the Nyquist frequency, which is only dependent on the sample rate. Decimating is the combination of low-pass filtering + downsampling (which is the term for discarding samples ...
• 6,055

### Why is aliasing inherently non-linear?

I think you mean "images", not "aliases". They become aliases if there is foldover from resampling. It's because you are not adding two signals, $x(t)$ and $\operatorname{III}(t)$, you are ...
Accepted

### Freeform band-limited waveforms

this paper was done long before i had MATLAB. the drawings are poor, but the math (at least in this revision, which is what you should use) is spot on. send me an email address (to my ...
Accepted

### Generating digitized white noise: uniform vs normal sampling

Your question is an interesting project for you to research it on your own. Well, maybe with a little help from your friend and the SE community. And, as your question goes, start with generating ...
• 1,729
Accepted

### Is spectral density conserved after aliasing?

No. The aliased component will interfere with the non-aliased components and the interference can constructive or destructive. Trivial example: $$x[n] = \sin\left(\frac\pi2n\right)$$ If you down ...
• 44.7k

• 51.3k
Accepted

### How do you sub-sample an FFT?

it seems like the bigger problem is that subsampling the signal would result in aliasing frequencies No, subsampling in frequency domain corresponds to aliasing in time domain. So the idea here is to ...
• 2,263