Digital sound revolution

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The digital sound revolution (or digital audio revolution) refers to the widespread adoption of digital audio technology in the computer industry beginning in the 1980s.

Contents 1 Prior methods 1.1 Software-based pulse-width modulation 1.2 FM synthesis 2 Digital-to-analog converters 3 Compression 4 Non-moving storage 5 Online music distribution 6 References

[edit] Prior methods

[edit] Software-based pulse-width modulation

Some of the first computer music was created in 1961 by LaFarr Stuart, who wrote software to modulate the duration of and between pulses (pulse-width modulation or "PWM", via a process now often referred to as "bit-banging") on a bus line that had been connected to an amplified speaker originally installed to monitor the functioning of Iowa State University's CYCLONE computer, a derivative of the Illiac. The entire computer was used to create simple, recognizable tunes using digital audio. A recording of an interview with Mr. Stuart and his computer music was broadcast nationally on the NBC radio network program Monitor (NBC Radio) on February 10, 1962.

The speakers in the IBM PC (released in 1981) and its successors may be used to create sounds and music using a similar mechanism.

[edit] FM synthesis

The first specialized audio circuits in computers included simple analog oscillators that could be set to desired frequencies, generally approximating tones along the musical scale. A base frequency was then modulated with analog filters to create desired effects; this process of audio waveform synthesis using frequency modulation is usually referred to as FM synthesis.

Early integrated circuit devices to incorporate FM synthesis methods include the Atari POKEY custom application-specific integrated circuit or "ASIC" (U.S. Patent 4,314,236 issued February 2, 1982^[1]) in the Atari 800 and the MOS Technology 6581/8580 SID chip (U.S. Patent 4,677,890, filed on February 27, 1983 and issued on July 7, 1987^[2]) used in the Commodore 64. The Yamaha OPL2 chip set (YM3812 and external digital-to-analog converter) was included on the AdLib sound card (1987), on the Creative Technology Sound Blaster (1989) and (in pairs, to create stereo sound) on the Media Vision Pro AudioSpectrum (1991); these were replaced by the next generation Yamaha OPL3 chip set on the Pro AudioSpectrum 16 and Sound Blaster 16.

[edit] 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 High Sierra Format, which became the basis for the 1988 CD-ROM data standard ISO 9660.

The Apple Macintosh (released in 1984), Commodore Amiga and Atari ST all used the Motorola 68000 as their CPUs and regularly produced digital audio.

The first computer to feature a digital sound processor was the Commodore Amiga released in 1985. The 8364 Paula chip featured four independent 8-bit D/A converters. This gave Paula four mono audio channels, or two combined stereo channels. This meant for the first time a computer could play digital samples from memory without heavy 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).

[edit] Compression

High fidelity audio hardware became inexpensive faster than data storage media, driving the development of compression techniques.

A popular early variant of pulse-code modulation ("PCM") was a compressed version called adaptive differential pulse-code modulation ("ADPCM").

Sound module files (originally Amiga .MOD files) enabled music to be created and shared via compact files and played back with high quality (using four channels, each at half the sampling rate of audio compact discs). Soon after the release of its Pro AudioSpectrum 16, Media Vision included with it a MOD file player and sample music files.

In the late 1990s, the MP3 format emerged, allowing music to be stored in relatively small files by using high compressions rates through a predictive synthesis technique. Modern computer CD-ROM drives allowed the redbook audio to be read in digital format (versus earlier drives that merely output analog audio), which allows entire volumes of music to be copied and encoded many times faster than normal playback speed.

[edit] Non-moving storage

After the year 2000, strong demand for small portable music players such as Apple's iPods drove competition in component sales, resulting in data storage devices becoming increasingly inexpensive. Ultimately, non-volatile semiconductor-based storage devices became less expensive than fixed hard disk drives.

[edit] Online music distribution

The popularity of high-quality compressed music and the widespread availability of Internet access enabled widespread copyright infringement (most notably through Napster) followed by widespread legitimate sales of music online through the Apple iTunes Music Store, Amazon.com, Walmart.com and others.

[edit] References