Not mentioned ...
Just like FM broadcasts, stereo audio is converted to Left+Right and Left-Right signals.
An MP3 process stores the L+R signal with more data and saves on the data for the L-R, difference channel.
“Just like FM broadcasts, stereo audio is converted to Left+Right and Left-Right signals.”
The L+R becomes the mono carrier for backwards compatibility and the L-R is used to derive the L and R channels from the L+R signal.
“An MP3 process stores the L+R signal with more data and saves on the data for the L-R, difference channel.”
Because most of the data is centered left and right are similar so L-R is very small.