Sound card

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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).

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General characteristics

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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.

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Connections

Most sound cards adhere 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)
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History

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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.

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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.

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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.

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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.

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.

As stated before, 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).

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Driver architecture

To use a sound card, a certain operating system typically requires a specific device driver.

  • DOS programs had to code the sound hardware directly or use universal middleware sound libraries (HMI Sound Operating System, Miles Sound System etc.) which had drivers for most common sound cards, although some manufacturers provided their own (pretty inefficient) middleware TSRs.
  • Microsoft Windows uses proprietary drivers supplied by sound card manufacturers and supplied to Microsoft for inclusion in the distributions. Sometimes drivers are also supplied by the individual vendors for download and installation.
  • The Linux kernel used in the Linux distributions have two different driver architectures, the Open Sound System and ALSA (Advanced Linux Sound Architecture). Both include drivers for most cards by default. Sound card manufacturers seldom produce stand-alone drivers for Linux.
  • The Universal Serial Bus (USB) specification defines a standard interface for sound cards to adhere to, the USB audio device class, allowing a single driver to work with the various USB sound cards on the market.
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See also

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References

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.
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External links

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