"Many mono recordings are just the same signal recorded on both channels that sum to mono. Mono cutter heads were often not rigid and wobble all over the place at high frequencies. Also the method of the design will affect how much vertical is by default engraved in the cut, Hence my jaundiced view on mono. When mono was all that was available then I accept them at face value."

"Get some old 1950s 78s and play them with a stereo cartridge with right channel wired out of phase then added together so you hear only the vertical or L-R component and be surprise how much rubbish is audible." - Tim de Paravicini