Hitler's Mannerheim monologue from 1942 comes to mind. Youtube link.

It was recorded in secret in 1942. I'll keep it brief here, since the details of the recording and circumstances are fairly well described in the youtube link. Here's an article from The Guardian discussing the circumstances of the tape a bit more. (Since a youtube link is not really a great source for anything, especially in this forum!) The tape contains the first the first 11 minutes of Adolf Hitler having a private conversation with Finland's General Carl Gustaf Emil Mannerheim.

It's the only recording of Hitler outside of a public speaking avenue. Obviously, he's not a ranting madman, but rather soft spoken and candid in his descriptions of the war effort to Mannerheim.

I recommend William Shirer's Rise and Fall of the Third Reich. It is thorough and enormous, if it is also somewhat of-its-time. Shirer was a journalist roughly analogous to Walter Cronkite if he had also had a diplomatic career. He spoke several languages and was either in the room or had the ear of the major players for lots of the major diplomatic shenanigans of the war. He was nowhere near Hitler's inner circle, but had descriptions of meetings, etc. from diverse witnesses, politicians, diplomats, etc. He finally set it all down in a book in ~1960 when he was about 80. While modern historians (who are born with a jaundiced view of journalists) quibble with many aspects of his work, it is still one of the major points of reference.

Back to your question - Hitler could manage both. Small talk with kids and cute young women was within his comfort zone. More often, he'd be in a room with other diplomats or big shots and it would be an endless monologue going into the night. (My observation, not Shirer's - this sounds a bit like the talking jags one would see in Breaking Bad occasionally, but from someone with a genius IQ.) A dozen times, IIRC, Shirer describes some ambassador's account of a party or something where Hitler would just do all the talking, and this poor guy would want to be home in bed, and Hitler just keeps going on and on until 2 am. Eye contact was also not really done. Hitler would chat with you as if he was delivering a speech most often, even if there were 4 of you in the room. Mussolini apparently also got this treatment.

When the need arose to affect a reasonable and calm tone, he could also lay on the oil pretty smooth and thick with Neville Chamberlain. This is when he was younger and healthier.