I was saving this part 'til last. Friend, colleague and fellow engineer Michael Pollard and yours truly got to sit in a seminar with the original engineer (Geoff Emerick) and tape op' (Richard Lush) for the Beatles' records at EMI London. Wow. Most of all an insight into the art form that is audio engineering, technical yet creative. Emerick in particular was often pushing boundaries, scolded by superiors at EMI for 'mistreating' equipment and harassed by the Beatles to constantly re-invent the wheel of sound capture during these famous years. At one point I spontaneously began to applaud as Lush stated "not once did we ever go back to source reels" when bouncing down their limited number of recording tracks to another 4 track recorder - truly wonderful.
Interestingly enough the most often used tools were microphone choice and position, dynamics and very limited eq. Gain structure also played an important role in sculpting the final sounds now heard around the world for decades. Inspirational.