Sound card

A sound card is a computer expansion card that can input and output sound under control of computer programs. Typical uses of sound cards include providing the audio component for multimedia applications such as music composition, editing video or audio, presentation/education, and entertainment (games). Many computers have sound capabilities built in, while others require these expansion cards if audio capability is desired.

General characteristics

A typical sound card includes a sound chip, usually featuring a digital-to-analog converter, that converts recorded or generated digital waveforms of sound into an analog format. This signal is led to a (typically 1/8-inch earphone-type) connector where an amplifier, headphones, or similar sound destination can be plugged in. More advanced designs usually include more than one sound chip to separate duties between digital sound production and synthesized sounds (usually for real-time generation of music and sound effects utilizing little data and CPU time).

Digital sound reproduction is usually achieved by multi-channel DACs, able to play multiple digital samples at different pitches and volumes, optionally applying real-time effects like filtering or distortion. Multi-channel digital sound playback can also be used for music synthesis if used with a digitized instrument bank of some sort, typically a small amount of ROM or Flash memory containing samples corresponding to the standard MIDI instruments. (A contrasting way to synthesize sound on a PC uses "audio codecs", which rely heavily on software for music synthesis, MIDI compliance and even multiple-channel emulation. This approach has become common as manufacturers seek to simplify the design and the cost of the sound card itself).

Most sound cards have a line in connector where the sound signal from a cassette tape recorder or similar sound source can be input. The sound card can digitize this signal and store it (controlled by the corresponding computer software) on the computer's hard disk for editing or further reproduction. Another typical external connector is the microphone connector, for connecting to a microphone or other input device that generates a relatively lower voltage than the line in connector. Input through a microphone jack is typically used by speech recognition software or Voice over IP applications.

Connections

Most sound cards since 1999 conform to Microsoft's PC 99 standard for color coding the external connectors as follows:

Color		Function
	Pink	Analog microphone input.
	Light blue	Analog line level input.
	Lime green	Analog line level output for the main stereo signal (front speakers or headphones).
	Black	Analog line level output for rear speakers.
	Orange	S/PDIF digital output (sometimes used as an analog line output for a center speaker instead)

History of Sound Cards for the IBM PC Architecture

Sound cards for computers based on the IBM PC remained uncommon until about 1988, leaving the internal PC speaker as the only way early PC games could produce sound and music. The speaker was limited to square wave production, leading to the common nickname of "beeper" and the resulting sound described as "beeps and boops". Several companies, most notably Access Software, developed techniques for digital sound reproduction over the PC speaker; the resulting audio, while functional, suffered from distorted output and low volume, and usually required all other processing to halt while sounds were played. Other home computer models of the 1980s included hardware support for digital sound playback or music synthesis (or both), leaving the IBM PC at a disadvantage when it came to multimedia applications such as music composition or gaming.

It is important to note that the primary design and marketing focus of sound cards for the IBM PC platform were not based on gaming, but rather on specific audio applications such as music composition (AdLib Personal Music System, Creative Music System, IBM Music Feature Card) or on speech synthesis (Digispeech DS201, Covox Speech Thing, Street Electronics Echo). It took the involvment of Sierra and other game companies in 1988 to switch the focus toward gaming.

Hardware Manufacturers

One of the first manufacturers of sound cards for the IBM PC was AdLib, who produced a card based on the Yamaha YM3812 sound chip, aka the OPL2. The AdLib had two modes: A 9-voice mode where each voice could be fully programmed, and a lesser-used "percussion" mode that used 3 regular voices to produce 5 independent percussion-only voices for a total of 11. (The percussion mode was considered inflexible by most developers, so it was used mostly by AdLib's own composition software.)

Creative Labs also marketed a sound card at the same time called the Creative Music System. Although the C/MS had twelve voices to AdLib's nine, and was a stereo card while the AdLib was mono, the basic technology behind it was based on the Philips SAA 1099 which was essentially a square-wave generator. Sounding not unlike twelve simultaneous PC speakers, it never caught on the way the AdLib did, even after Creative marketed it a year later through Radio Shack as the Game Blaster. The Game Blaster retailed for under $100 and included the hit game title Silpheed.

Probably the most significant historical change in the history of sound cards came when Creative Labs produced the Sound Blaster card. The Sound Blaster cloned the AdLib, and also added a sound coprocessor to record and play back digital audio (presumably an Intel microcontroller, which Creative incorrectly called a "DSP" to suggest it was a digital signal processor), a game port for adding a joystick, and the ability to interface to MIDI equipment (using the game port and a special cable). With more features at nearly the same price point, and compatibility with existing AdLib titles, most first-time buyers chose the Sound Blaster. The Sound Blaster eventually outsold the AdLib and set the stage for dominating the market.

The Sound Blaster line of cards, in tandem with the first cheap CD-ROM drives and evolving video technology, ushered in a new era of multimedia computer applications that could play back CD audio, add recorded dialogue to computer games, or even reproduce motion video (albeit at much lower resolutions and quality). The widespread adoption of Sound Blaster support in multimedia and entertainment titles meant that future sound cards such as Media Vision's Pro Audio Spectrum and the Gravis Ultrasound needed to address Sound Blaster compatibility if they were to compete against it.

Industry Adoption

When game company Sierra Entertainment (known then as Sierra On-Line) opted to make music for add-on hardware instead of utilizing the built in PC-speaker, the concept of PC sound and music changed dramatically. The two companies Sierra eventually started to cooperate with were Roland and Adlib. Sierra opted to make in-game music, starting with King's Quest 4, for the Roland MT-32 and Adlib Music Synthesizer. The MT-32 was far superior as it boasted a synthesizer that could combine small wave samples with synthesized sounds, and it had excellent reverb. Sierra really made the most of the MT-32, and nearly every game loaded custom patches onto the synth to produce sound effects for things like birds chirping and horses clopping in the age before the Sound Blaster brought the possibility of playing such things as audio clips to the PC world. The MT-32 was able to deliver much better sound reproduction than the FM chip residing in the Adlib soundcard. The popularity of MT-32 lead the way for the adoption of MPU-401/Roland Sound Canvas and General MIDI standards as the definitive means of playing in-game music until mid-1990s.

Feature Evolution

Most ISA bus soundcards could not record and play digitized sound simultaneously, partially due to lack of available hardware interrupts and DMA channels, and partially due to inferior card DSPs. Later PCI bus cards fixed these limitations and are mostly full-duplex.

For years, soundcards had only one or two channels of digital sound (most notably the Soundblaster series and their compatibles) with the notable exception of the Gravis Ultrasound family, which had hardware support for 14 to 32 independent channels of digital audio, and early games and MOD-players had to fully emulate multiple channels by software downmixing. Today, most good quality sound cards have hardware support for at least 16 channels of digital audio, but others, like those that utilize cheap Audio codecs, still rely partially or completely on software through either device drivers or the operating system itself to perform a software downmix of multiple audio channels.

Sound Cards that aren't Sound Cards

Integrated Sound on the PC

In the late 1990s, many computer manufacturers began to replace plug-in soundcards with a "codec" (actually a combined audio AD/DA-converter) integrated into the motherboard. Many of these used Intel's AC97 specification. Others used cheap ACR slots. These integrated sound systems appear to the operating system to be plug-in soundcards so that no software changes are needed to use them.

As of 2005, these "codecs" usually lack the hardware for direct music synthesis or even multi-channel sound, with special drivers and software making up for these lacks, at the expense of CPU speed (for example, MIDI reproduction takes away 10-15% CPU time on an Athlon XP 1600+ CPU).

Integrated Sound on Other Platforms

Various computers which do not use the IBM PC architecture, such as the Apple Computer Macintosh and Workstations from manufacturers like Sun have had their own motherboard integrated sound devices. In some cases these provide very advanced capabilities (for the time of manufacture), in most they are minimal systems. Some of these platforms have also had sound cards designed for their bus architectures which of course cannot be used in a standard PC.

USB Sound Cards

While not literally sound cards (since they don't plug into slots inside of a computer, and usually are not card-shaped (rectangular)), there are devices called USB Sound Cards. These attach to a computer via USB cables. The USB specification defines a standard interface, the USB audio device class, allowing a single driver to work with the various USB sound devices on the market.

Other Outboard Sound Devices

USB Sound Cards are far from the first external devices allowing a computer to record or synthesize sound. Virtually any method that was once common for getting an electrical signal in or out of a computer has probably been used to attempt to produce sound.

Driver architecture

To use a sound card, the operating system typically requires a specific device driver. Some operating systems include the drivers for some or all cards available, in other cases the drivers are supplied with the card itself, or are available for download.

DOS programs for the IBM PC often had to use universal middleware driver libraries ([such as [HMI Sound Operating System]], Miles Sound System etc.) which had drivers for most common sound cards, since DOS itself had no real concept of a sound card. Some card manufacturers provided (pretty inefficient) middleware TSR-based drivers for their products, and some programs simply had drivers incorporated into the program itself for the sound cards that were supported.
Microsoft Windows uses proprietary drivers generally written by the sound card manufacturers. Many makers supply the drivers to Microsoft for inclusion on Windows distributions. Sometimes drivers are also supplied by the individual vendors for download and installation. Bug fixes and other improvements are likely to be available faster via downloading, since Windows CDs cannot be updated as frequently as a web or ftp site.
Linux has two different driver architectures, the older Open Sound System and the newer ALSA (Advanced Linux Sound Architecture). Both include drivers for most cards by default. Sound card manufacturers seldom produce stand-alone drivers for Linux.

References

This article is based on material taken from the Free On-line Dictionary of Computing prior to 1 November 2008 and incorporated under the "relicensing" terms of the GFDL, version 1.3 or later.

External links