Oh, and it's not a "measure" of what's different between two voices (be they human or instrumental) producing a sound with a fundamental frequency at 440 Hz. They are two completely different waveforms. It's only the slowest part of the waveform that's cycling at 440 times a second. That's what gives any instrument its unique timbre.

But it is possible to digitally capture and accurately reproduce any of those sounds that exist below the Nyquist of the sampling system.
Pioneer VSX-1018AH-K, PDP-5020FD, DV-79AVi
Axiom M22s, VP150, QS8s
Sony PS3, surround backs