Reducing leakage of backing track to vocal microphone must had helped singers to sing in tune

This must have been a very helpful for exact intonation byproduct.


If there is low acoustic intensity level of the backing track or live orchestra to the mic this means there is a low acoustic level to the singer's ear too.


This means the singer can hear a true pitch as pitch does not only depend on frequency but on intensity too. This is how our ear-brain perception works.


Every measure taken to reduce leakage, for example:


Singer without headphones in a semi open vocal booth near the orchestra.


Singer listening through a small speaker near to them (the Bee Gees).


Orchestra playing at soft levels,


etc,


must have helped for the spot on tuning performances we hear on some recordings.


It is easy to verify this by having for example a radio playing in the room and singing along and then reducing the volume of the radio to a very low level. Or having the radio in a room and singing in another room and then closing the door between the rooms.


A similar experiment can be made with listening to headphones at very low levels.


Reference:


Sound and Hearing - Stevens, Warshofsky - Time-Life Books