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Sample Rate

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Audio Basis - educational articles

Simple about what is sample rate and Nyquist–Shannon sampling theorem

Sound is air pressure oscillation.

The oscillation is fast changing of air pressure in time.

Air oscillations become to microphone and changing of air pressure transform to changing of electrical voltage.

Analog-digital converter make measurements of voltage (samples) at each instant.

The measurements become to digital audio recording device.

Sample rate is number samples per second.

More sample rate - more samples per second.

Complex signal always consists some simple sine signals.

 

 

What is sine signal?

Sine signal is periodic. Changing of voltage (values 0 - 1 - 0 - -1 or UP - GROUND - DOWN) repeat via time period.

As swing of the pendulum: center - left - center - right, center - left - center - right.
Sine voltage: 0 - 1 - 0 - -1, 0 - 1 - 0 - -1.

Frequency of sine is number repeating (0 - 1 - 0 - -1) per second.
More sine frequency - more high sound.

 



What is Nyquist–Shannon sampling theorem?

We have period between the samples.

Designate this period as sampling period.

Imagine sine with the one repeating during the two sampling periods.

Nyquist–Shannon sampling theorem say:

It most high frequency (high sound) which be able to converted to digital form.

 

 

Sample rate and "stairs"

At first sight, digital signal like to "stairs". But, really, it is not so.

"Stairs" exists after conversion digital values to electrical voltage.

But next stage is analog filtering.

The filtering smooth stairs (interpolate). It is like to connecting voltage values by steel ruler.

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