Nyquist theorem
Nyquist’s theorem relates to the sampling of an analogue signal to create a digital signal.
It states that:
To accurately sample an analogue signal, the sampling rate must be at least twice the highest frequency present in the analogue signal.
For music and voice audio, the highest frequency is usually around 20,000 Hz (20 kHz), which is why CD quality audio has a sample rate of 44,100 samples per second! It’s designed to be about double the highest frequency in the audio, to make sure that we can accurately capture the sound without losing any important information.
Example
If the highest frequency in an audio track is 12kHz, the minimum sample rate needed to produce an accurate digital sound is 24kHz - twice as high.
flashcards
| Question | Answer |
|---|---|
| Nyquist theorem definition | To accurately sample an analogue signal, the sampling rate must be at least twice the highest frequency present in the analogue signal. |
| What is the purpose of Nyquist’s theorem? | It relates the sampling of an analogue signal to create a digital signal. |
| Why is CD quality audio sampled at 44,100 samples per second? | Because the highest frequency in music and voice audio is usually around 20 kHz, and 44.1 kHz is about double that frequency to ensure accurate capture without losing information. |
| If the highest frequency in an audio track is 12 kHz, what is the minimum sample rate needed to produce an accurate digital sound? | 24 kHz (twice as high as 12 kHz). |