"Hitler visited Finnish Field Marshal Mannerheim on 4 June 1942. During the visit an engineer of the Finnish broadcasting company YLE, Thor Damen, recorded Hitler and Mannerheim in conversation, something which had to be done secretly since Hitler never allowed recordings of him off-guard. Today the recording is the only known recording of Hitler not speaking in an official tone. The recording captures 11½ minutes of the two leaders in private conversation. Hitler speaks in a slightly excited, but still intellectually detached manner during this talk (the speech has been compared to that of the working class). The majority of the recording is a monologue by Hitler. In the recording, Hitler admits to underestimating the Soviet Union's ability to conduct war." - Wikipedia
Hitler seems to be one of those people who you realise you've never heard speak normally before.