Complex sentence: In 1952, sound engineer Emory Cook developed a stereophonic disk that used two separate grooves and playback needles; the following year he had a catalog of about 25 disks available for audiophiles.
Split into simpler sentences: In 1952, sound engineer Emory Cook developed a stereophonic disc that used two separate grooves and playback needles. The following year he had a catalog of about 25 disks available for audiophiles.