So according to the way we do things then, the bandwidth or the spectrum of – a slice of spectrum of music would go roughly up to say 20,000 hertz and then down to minus 20,000, so the frequency would be – and beyond that it’s essentially zero. At least as far as you’re concerned it’s zero. You can’t hear anything. So if that’s a picture of the spectrum of a slice of music, then it’s between minus 20,000 and 20,000, so the way we write things, that would be P over 2. The bandwidth is 20,000, so P is about 40,000, which means that if you wanna sample and reconstruct music, you should do it roughly at a rate of 40,000 hertz. ...

See the whole transcript at The Fourier Transform and its Applications - Lecture 19