Downsampling Audio, Decimation [Explained]
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Downsampling Audio, Decimation [Explained]

Audio Basis - articles about audio

yuri korzunovDownsampling is kind of sample rate conversion - dividing frequency (decimation of samples). Read how to work downsampling.
Author: audio software developer Yuri Korzunov.


How to work downsampling

How to divide sample frequency (downsampling) two times? Every second sample of source signal is simply removed.

Downsampling on time axis


Sound quality

Output spectrum we see on bottom of the picture. Light blue area of source spectrum mirrored on spectrum of audio with divided sampling rate. It is non-linear distortions arose in useful spectrum band after dividing sampling rate.


Spectrum audio after downsampling


On top of the picture we see spectrum of source audio signal with sampling rate Fd. Spectrum on probation contains 2 areas (blue and light blue). We see what light blue placed above Fd/4.

We will decrease (divide 2 times) sample rate source audio and watch to metamorphoses of its spectrum. New sample rate is Fd new = Fd / 2.


Possible avoid it?

Yes. Before dividing need filter (suppress) source spectrum above Fd new / 2 = Fd / 4.

Downsampling with filtering

About oversampling read here...



Read about sample rate issues


Frequently Asked Questions

What is downsampling in audio?

Downsampling in aduio is reducing of sampling rate of an audio stream/file. Read more...


Does downsampling reduce audio quality?

Downsampling lose some information of audio due to lost sampling rate difference. If target sampling rate above 44.1 kHz, you can don't worry about audible range.

Proper resampling tool almost don't cause additional losses. Read details...


What is the effect of downsampling?

Downsampling loses sound information and it should degrade sound.

In the case of target band more 20 kHz, proper downsampling should not cause audible effect.

But some nuances are there. Read details...


June 28, 2022 updated | since June 17, 2014

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