Embedded Systems Design, 2nd Edition

Interfacing to the analogue world 179

Nyquist’s theorem

The sample rate also must be chosen carefully when consid-

ering the maximum frequency of the analogue signal being con-

verted. Nyquist’s theorem states that the minimum sampling rate

frequency should be twice the maximum frequency of the ana-

logue signal. A 4 kHz analogue signal would need to be sampled

at twice that frequency to convert it digitally. For example, a hi-fi

audio signal with a frequency range of 20 to 20 kHz would need a

minimum sampling rate of 40 kHz.

Higher frequency sampling introduces a frequency compo-

nent which is normally filtered out using an analogue filter.

Codecs

So far ...