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Downsampling Audio, Decimation [Explained]

Audio Basis - educational articles

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

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

 

 


Read the articles
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How to Convert ISO to FLAC on Mac OSX, Windows [Step-by-step Guide]
How to Convert ISO to DSF on Mac OS, Windows [Step-by-step Guide]
How to Choose the Best Audio Converter Software [Article]

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