Throughout the 1970's the quality of cinema sound was held inferior to that of music production due to economic reasons. There simply wasn't enough economic stimulus for the film studios to adopt better technologies at a rate that might have been feasible.
Home video and cable TV was
also becoming more widespread during this time,
enabling people to not only listen to music but watch movies at home as
well. The merging of the music and film industries had been nearly completed
on an institutional level by this era. For example, EMI Studios produced
both music and movies, including the music of Pink
Floyd and the films of Stanley
Kubrick. Of course the music, radio, movie, and television industries
had been closely related throughout the twentieth century. The movie industry
and music industry were closer and more similar than ever.