Before the digital revolution, sound was recorded on cassette tapes and records.  The cassette tape represented a considerable improvement over the record, but it still relied on analog sound.  An entire sound wave was recorded—either on the record disc or the magnetic tape—and then played back in its entirety in a record or cassette player.

The problem with analog sound was that it didn’t only pick up the desired sound.  It also picked up background noises and interference, making the sound quality less than perfect.

CD’s use “digital sound”: an advance that relies on a technology called PCM, or Pulse Control Modulation.  With PCM, a sound wave would be “sampled” or recorded in bits of discrete data, like dots on a graph.  A reading device—in the case of CD’s and DVD’s, a laser—would read the data and connect the dots, reproducing the sound.  

PCM technology had been around in a theoretical sense for decades—but engineers could never find a way to apply it practically.  Surprisingly, the video application came before the audio.  The first recording device to use PCM was the Laserdisc, which often used analog video and digital audio.  The Laserdisc offered considerably sharper visuals than the dominant technology of the time, the video cassette.

In 1979, Sony and Philips combined forces to create the first digital audio CD’s.  While Laserdiscs were very sensitive to dust and scratches, CD’s had a higher tolerance for handling and were more durable.  They also incorporated error correction technology.

The first CD’s were marketed in 1982 in Asia and in 1983 in the U.S.  At first, serious music aficionados—particularly fans of classical music—were the primary buyers in the U.S.  As the prices fell and CD players became more affordable, they began to take over the rock and youth markets as well.