I'm a huge fan of Alan Parsons as a producer (he's the guy who was behind the controls of Al Stewart's "Year of the Cat," still one of the best sounding LPs I've ever heard.) 

He was also the man who turned out Pink Floyd's seminal album "Dark Side of the Moon." Probably the most famous cut from that LP is the tune "Money," which starts with the sound of cash registers ringing and coins clinking. It's an amazing piece of work and I've often wondered how they managed to get it done so perfectly, especially in those tape-only days. 

Now an old article I stumbled upon has answered the question and it shows how incredibly complex the entire process was. But all these years later, it's still brilliant. 

"We had to assemble a loop that worked, timing-wise, for all of those different sounds. The only way to keep it in time was to take a piece of tape with the sound on it and measure it with a ruler. You would take the exact length of tape and then splice the next exact length of tape onto it. We would make circular loop that was supported with microphone stands around the machine, and we would roll the tape, and that was what the band played to."

The story contains a lot of other revelations about the making of this legendary album, which celebrated its 50th anniversary this year. You can read it here:

Spend time on 'The Dark Side of the Moon' with Alan Parsons