Yup, the #1 used computerized control, but all the switching was still electromechanical, so it sounded like a typewriter factory, especially during busy-hour.

Yup, the #1 used computerized control, but all the switching was still electromechanical, so it sounded like a typewriter factory, especially during busy-hour. At night, traffic was often low enough that you could hear individual call setups and teardowns, each a cascade of relay actuations rippling from one part of the floor to another. The junctor relays in particular were oddly hefty and made a solid clack, twice per call setup if I recall correctly, once to prove the path by swinging it over it to a test point of some sort, and then again to actually connect it through. On rare occasion, you'd hear a triple-clack as the first path tested bad, an alternate was set up and tested good, and then connected through. Moments after such a triple-clack, one of the teleprinters would spring to life, spitting out a trouble ticket indicating the failed circuit. The #5, on the other hand, was completely electronic, time-division switching in the core. The only clicks were the individual line relays responsible for ringing and talk battery, and these were almost silent in comparison. You couldn't learn anything about the health of the machine by just standing in the middle of it and listening, and anyone in possession of a relay contact burnishing tool will tell you in no uncertain terms, that the #5 has no soul.