Nyquist theorem
Nyquist theorem says that to accurately reproduce sounds recorded electronically that the sample rate must be at least double the highest frequency.
A sound frequency of 1000Hz would need to be recorded at a minimum of 2000Hz to be recorded correctly.
The average human ear can hear frequencies between 20Hz and 20000Hz.
Because some peoples hearing is slightly more sensitive, CDs are sampled at 44100Hz.
MIDI (Musical instrument digital interface)
A MIDI controller carries event messages.
Typical event messages might include pitch, duration, volume, instrument etc.
MIDI allows a small number of people to create the sound of a much larger group.
A MIDI file is generally much smaller in size than its recorded equivalent.
MIDI files can be easily manipulated e.g. playing as another instrument or in a different key.
