3. Sampling frequency

This is the rate at which samples are taken - stated in Kilohertz (thousand times per second).

What happens if the samples are taken too slowly compared to the sound signal?

Have a look at the extreme example below. where the white arrows are regularly spaced samples.

The table of values recorded are shown below.

sample	Measurement
1	0.7
2	0.7
3	0.7

Every value is the same! All the frequency information of the sound has been missed. This shows that there is a minimum rate at which samples need to be taken in order to faithfully reproduce the original signal.

The minimum sampling rate is at least twice the highest frequency in the signal.

So for a CD that has sound going up to 20KHz, the minimum sampling rate is 40 KHz. Things are not perfect, so the music industy uses 44.1KHz

Challenge see if you can find out one extra fact on this topic that we haven't already told you

Click on this link: what is the Nyquist frequency