Digital-to-analog Converters
As they became more cost-effective, digital-to-analog converter (often called "D-to-A"--abbreviated "D/A", or "DAC") integrated circuits augmented and ultimately replaced FM synthesis devices. These devices enabled computers to play digital audio using an encoding technique known as pulse-code modulation ("PCM"). Unlike pulse-width modulation ("PWM"), which turns a signal on and off, pulse-code modulation also allows the level of a signal to be set to several intermediate levels; in this regard, PWM and PCM are similar to black-and-white and grayscale images, respectively.
Digital audio compact discs (using PCM) were introduced in 1982. Starting in 1985, the medium was adapted for the storage of computer data via the Yellow Book and the High Sierra Format, which became the basis for the 1988 CD-ROM data standard ISO 9660.
The Apple Macintosh (1984) and Atari ST (1985) could produce digital audio via software. Without dedicated audio hardware, digital audio on these machines were usually limited to title screens in games (at higher sampling rates) or games which did not feature heavy animation which left enough CPU time to play lower quality samples.
The first computer to feature a digital sound processor was the Commodore Amiga released in 1985. The MOS Technology 8364 Paula chip featured four independent 8-bit D/A converters. The Paula features four mono audio channels, or two combined stereo channels. This meant for the first time a computer could play digital samples from memory with virtually no CPU usage, or any clever software tricks.
In 1989, the Creative Technology Sound Blaster featured a processor and digital-to-analog converter, and incorporated the Yamaha OPL2 chip set FM synthesis devices for compatibility with the AdLib sound card. In 1991, Media Vision introduced the original Pro AudioSpectrum, which offered similar functionality but introduced stereo sound, an audio mixer and CD-ROM interface (SCSI and many variants); its 16-bit successor, the Pro AudioSpectrum 16, offered CD-quality sound via its 16-bit compressor-decompressor ("CODEC").
In 1997, Intel Corporation created its Audio CODEC standard AC'97, which was superseded in 2004 by Intel High Definition Audio (HD Audio).
Read more about this topic: Digital Sound Revolution