Aliasing in audio signals

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In signal processing and related disciplines, aliasing is an effect that causes different signals to become indistinguishable (or aliases of one another) when sampled. It also refers to the distortion or artifact that results when the signal reconstructed from samples is different from the original continuous signal.

When audio is downsampled improperly, high frequencies will turn into lower ones and the audio will sound extremely distorted. It's a great proxy for what happens to performance data when it's improperly sampled.

Hodgson, J. (2020, 14. August). The "Sound " of Performance Monitoring, Part 2: Aliasing. Aternity. https://www.aternity.com/blogs/the-sound-of-performance-data-part-2/

music_spectrum

Original audio signal with full bandwidth.
 


Sample rate: 44,100 - file size: 128,000 bytes + wav header
music_spectrum_with_alias_effect

Reducing the sample rate by 8 produces an aliasing effect.
Do you see it in the spectrum, can you hear it?


Sample rate: 5,512.5 - file size: 16,000 bytes + wav header

Original audio signal with reduced bandwidth (2.5 kHz).
An anti-aliasing filter is used before sampling.


Sample rate: 44,100 - file size: 128,000 bytes + wav header

Now, reducing the sample rate not produces an aliasing effect. Can you hear the difference?


Sample rate: 5,512.5 - file size: 16,000 bytes + wav header

There is an infinite number of aliases for every sampled frequency. Any sine wave is indistiguishable from an infinite number of sine waves after sampling.

We force aliasing to occur an inharmonic roughness in the audio signal.

Akash Murthy. (2020, 5. Mai). 4. Understanding Aliasing - Digital Audio Fundamentals [Video]. YouTube. https://www.youtube.com/watch?v=91PKZllbgds