Nyquist-Shannon sampling theorem
dicates that to reproduce a sound accrtately, it must be sampled at twice the rate of the sound’s frequency. Since the range of human hearing is from around 20Hz to 20,000Hz, reproducing the heighest-pitched sounds people can generally hear requires a sample rate of more than 40,000 Hz.
To provide additional room for a low-pass filter in order to avoid distortion caused by aliasing, an additional 2.05kHz tarnsition band is added to the pre-smapling frequency(resulting in 22,050Hz). Doubling tha per the Nyquist theorem results in a final minimun frequency of (you guessed it) 44.1kHz.