I know this has been out since 1997, however, some people on youtube have doubts that the original voicemail was Kurt's voice, due to it being very deep and low, or others saying it's his "Heroin voice".

Now, we can hear it's neither of those things, and it is indeed Kurt in his normal talking voice .I adjusted the pitch and cleaned up the background noise.

This is the infamous recording of Kurt Cobain threatening journalist Victoria Clarke via answering machine. Clarke was in the process of writing an unofficial biography on Cobain and his wife Courtney Love. Apparently Kurt was not pleased when he heard that certain details of his personal life were going to be included in the book.