Sampling frequency of voice and audio
It's the human hearing which defines associated bandwidths. Then the sampling frequency will be chosen to be larger than twice the bandwidth for satisfying the sampling theory and still as small as possible to reduce processing costs.

Human hearing for the general sound signals is accepted to be between 20 Hz and 20 kHz. The limits depending on individual, age, gender etc.

Note that various mechanical devices, acoustical instruments or alike can produce sound waves that are well in excess of 20 kHz upper limit and include ultrasound, however, an ordinary human will not be able to hear that, that's why the upper limit is taken to be 20 kHz.

For speech used in old analog communication (telephony audio) network, the intention was to find the minimum intelligible bandwidth to reduce the technical complexity and economic cost of building that network. This bandwidth is found to be within 300-3000 Hz. However as technology improved and other means of speech communication emerged, higher bandwidth audio was also used for better quality transmission. Digital codecs, radio broadcast etc. can use 8 kHz, 16 kHz etc. bandwidths too.