Oversampling, Upsampling Audio [How It Works and Sound]
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Oversampling, Upsampling Audio [How It Works and Sound]

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yuri korzunovOversampling (upsampling) is sample rate multiplication. As rule, oversampling is meant as multiple sample rate increasing. There is opinion, that non-multiple sample rate increasing cause cound degrading. Read how oversampling works and is sound advantages or disadvantages there.
Author: audio software developer Yuri Korzunov.


Usually multiplexing of sample rate released as inserting ZERO SAMPLES (virtual samples) between "real" source samples.

Oversampling. Upsampling


After oversampling spectrum mirrored to upper half of old sample rate fd. So we get mirrored copy of source audio spectrum (upper part of picture).

Oversampling - sample rate miltiplying


Resampling filters

It is non-linear distorttions in output (oversampled) audio signal.

For getting non-distorted (almost non-distorted, of course) oversampled audio signal, after oversampling need apply low frequency filtration with band from 0 to fd/2.

Filtering audio signal after oversampling


Sound quality

Sound quality of oversampling or upsampling defined by resampling filters.

In ideal case, all mirrored audio content should be suppressed, but audio content below [input sampling rate]/2 should be removed.

But there is no ideal resampling filters. And unwanted mirrored audio content folded to audible range and cause distortions.

Also, digital filters cause ringing and frequency distortions.

However, author don't know about serios studies, that prove actual ringing harm. And frequency distortions may be reduced significantly below human perceptions.

Digital filter have several contradictory features. And filter design is balance of the parameters, that is art of development.

So, with proper resampling filters, we get almost clean oversampled source audio signal (music).


Read more:



Read about sample rate issues



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