When the master disc for an album
is being cut, the music signal from the digital tape recorder is
"dbx encoded". This involves compressing, linearly in
decibels, all levels of the audio signal by one-half over the entire
frequency spectrum. By doing this, the signal can easily fit within
the dynamic range storage capability of the vinyl disc.
During playback through an
inexpensive decoding unit connected to a stereo system, the signal
picked up by the phono cartridge is linearly expanded in a
mirror-image fashion so that the dynamic range of the original music
signal is completely restored, and in the process, record surface
noise is eliminated for all practical purposes.