Sound card

A sound card is an internal expansion card that provides input and output of audio signals to and from a computer under the control of computer programs. The term sound card is also applied to external audio interfaces used for professional audio applications.
Sound functionality can also be integrated into the motherboard, using components similar to those found on plug-in cards. The integrated sound system is often still referred to as a sound card. Sound processing hardware is also present on modern video cards with HDMI to output sound along with the video using that connector; previously, they used a S/PDIF connection to the motherboard or sound card.
Typical sound card functionality includes providing the audio component for multimedia applications such as music composition, editing video or audio, presentation, education and entertainment and video projection. Sound cards are also used for computer-based communication such as voice over IP and teleconferencing.

General characteristics

Sound cards use a digital-to-analog converter, which converts recorded or generated digital signal data into an analog format. The output signal is connected to an amplifier, headphones, or external device using standard interconnects, such as a TRS phone connector.
A common external connector is the microphone connector. Input through a microphone connector can be used, for example, by speech recognition or voice over IP applications. Most sound cards have a line in connector for an analog input from a sound source that has higher voltage levels than a microphone. In either case, the sound card uses an analog-to-digital converter to digitize this signal.
Some cards include a sound chip to support the production of synthesized sounds, usually for real-time generation of music and sound effects using minimal data and CPU time.
The card may use direct memory access to transfer the samples to and from main memory, from where a recording and playback software may read and write it to the hard disk for storage, editing, or further processing.

Sound channels and polyphony

An important sound card characteristic is polyphony, which refers to its ability to process and output multiple independent voices or sounds simultaneously. These distinct channels are seen as the number of audio outputs, which may correspond to a speaker configuration such as 2.0, 2.1, 5.1, or other configurations. Sometimes, the terms voice and channel are used interchangeably to indicate the degree of polyphony, not the output speaker configuration. For example, much older sound chips could accommodate three voices, but only one output audio channel, requiring all voices to be mixed together. Later cards, such as the AdLib sound card, had a 9-voice polyphony combined in 1 mono output channel.
Early PC sound cards had multiple FM synthesis voices, which were used for MIDI music. The full capabilities of advanced cards are often not fully used; only one or two voice and channel are usually dedicated to playback of digital sound samples, and playing back more than one digital sound sample usually requires a software downmix at a fixed sampling rate. Modern low-cost integrated sound cards, such as audio codecs like those meeting the AC'97 standard and even some lower-cost expansion sound cards still work this way. These devices may provide more than two sound output channels, but they usually have no actual hardware polyphony for either sound effects or MIDI reproduction these tasks are performed entirely in software. This is similar to the way inexpensive softmodems perform modem tasks in software rather than in hardware.
In the early days of wavetable synthesis, some sound card manufacturers advertised polyphony solely on the MIDI capabilities alone. In this case, typically, the card is only capable of two channels of digital sound and the polyphony specification solely applies to the number of MIDI instruments the sound card is capable of producing at once.
Modern sound cards may provide more flexible audio accelerator capabilities which can be used in support of higher levels of polyphony or other purposes such as hardware acceleration of 3D sound, positional audio and real-time DSP effects.

List of sound card standards

Name	Year	Audio bit depth	Sampling frequency	Type	Channels
PC speaker	1981	≈6 bit	≈18.9 kHz	PWM	1 pulse-width modulation
PCjr	1984	16 volume settings	122 Hz to 125 kHz	PSG	3 square wave tone; 1 white noise
Tandy 1000	1984	16 volume settings / 6 bit	122 Hz to 125 kHz	PSG	3 square wave tone; 1 white noise; 1 pulse-width modulation
MPU-401	1984			MIDI	1 MIDI in; 2 MIDI out; DIN sync out; tape sync IO; metronome out
Covox Speech Thing	1987	8 bit	7 kHz, up to 44 kHz	PCM	1 DAC
AdLib	1987	64 volume settings / 8 bit	16 kHz	FM synthesizer	6-voice FM synthesizer, 5 percussion instruments
Roland MT-32	1987	16 bit	32 kHz	MIDI synthesizer	8 melodic channels; 1 rhythm channel
Sound Blaster	1989	8 bit	22.05 kHz	FM synthesizer + DSP	1 DAC; 11-voice FM synthesizer
Innovation SSI-2001	1989	8 bit	3906.19 Hz max.	PSG	3 voices
Sound Blaster Pro	1991	8 bit	44.1 kHz mono, 22.05 kHz stereo
Roland Sound Canvas	1991	16 bit	32 kHz	MIDI synthesizer	24 voices
Gravis UltraSound	1992	16 bit	44.1 kHz	Wavetable synthesis	16 stereo channels
AC'97	1997	24 bit	96 kHz	PCM + DSP	6 independent output channels
Environmental Audio Extensions	2001			Digital signal processing	8 simultaneous 3D voices
Intel High Definition Audio	2004	32 bit	192 kHz	PCM + DSP	up to 15 independent output channels

Color codes

Connectors on the sound cards are color-coded as per the PC System Design Guide. They may also have symbols of arrows, holes and soundwaves that are associated with each jack position.

History of sound cards for the IBM PC architecture

Sound cards for IBM PC–compatible computers were very uncommon until 1988. For the majority IBM PC users, the internal PC speaker was the only way for early PC software to produce sound and music. The speaker hardware was typically limited to square waves. The resulting sound was generally described as "beeps and boops" which resulted in the common nickname beeper. Several companies, most notably Access Software, developed techniques for digital sound reproduction over the PC speaker, like RealSound. The resulting audio, while functional, suffered from the heavily distorted output and low volume, and usually required all other processing to be stopped while sounds were played. Other home computers of the 1980s, like the Commodore 64, included hardware support for digital sound playback or music synthesis, leaving the IBM PC at a disadvantage when it came to multimedia applications. Early sound cards for the IBM PC platform were not designed for gaming or multimedia applications, but rather on specific audio applications, such as music composition with the AdLib Personal Music System, IBM Music Feature Card, and Creative Music System, or on speech synthesis like Digispeech DS201, Covox Speech Thing, and Street Electronics Echo.
In 1988, a panel of computer-game CEOs stated at the Consumer Electronics Show that the PC's limited sound capability prevented it from becoming the leading home computer, that it needed a $49–79 sound card with better capability than current products, and that once such hardware was widely installed, their companies would support it. Sierra On-Line, which had pioneered supporting EGA and VGA video, and 3-1/2" disks, promised that year to support the AdLib, IBM Music Feature, and Roland MT-32 sound cards in its games. A 1989 Computer Gaming World survey found that 18 of 25 game companies planned to support AdLib, six Roland and Covox, and seven Creative Music System/Game Blaster.

Hardware manufacturers

One of the first manufacturers of sound cards for the IBM PC was AdLib, which produced a card based on the Yamaha YM3812 sound chip, also known as the OPL2. The AdLib had two modes: A 9-voice mode where each voice could be fully programmed, and a less frequently used percussion mode with 3 regular voices producing 5 independent percussion-only voices for a total of 11.
Creative Labs also marketed a sound card called the Creative Music System at about the same time. 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 SAA1099 chip, which was essentially a square-wave generator. It sounded much like twelve simultaneous PC speakers would have except for each channel having amplitude control, and failed to sell well, even after Creative renamed it the Game Blaster a year later, and marketed it through RadioShack in the US. The Game Blaster retailed for under $100 and was compatible with many popular games, such as Silpheed.
A large change in the IBM PC-compatible sound card market happened when Creative Labs introduced the Sound Blaster card. Recommended by Microsoft to developers creating software based on the Multimedia PC standard, the Sound Blaster cloned the AdLib and added a sound coprocessor for recording and playback of digital audio. The card also included a game port for adding a joystick, and the capability to interface to MIDI equipment using the game port and a special cable. With AdLib compatibility and more features at nearly the same price, most buyers chose the Sound Blaster. It eventually outsold the AdLib and dominated the market.
Roland also made sound cards in the late 1980s such as the MT-32 and LAPC-I. Roland cards sold for hundreds of dollars. Many games, such as Silpheed and Police Quest II, had music written for their cards. The cards were often poor at sound effects, such as laughs, but for music were by far the best sound cards available until the mid-nineties. Some Roland cards, such as the SCC, and later versions of the MT-32, were made to be less expensive.
By 1992, one sound card vendor advertised that its product was "Sound Blaster, AdLib, Disney Sound Source and Covox Speech Thing Compatible!" Responding to readers complaining about an article on sound cards that unfavorably mentioned the Gravis Ultrasound, Computer Gaming World stated in January 1994 that, "The de facto standard in the gaming world is Sound Blaster compatibility... It would have been unfair to have recommended anything else." The magazine that year stated that Wing Commander II was "Probably the game responsible" for making it the standard card. The Sound Blaster line of cards, together with the first inexpensive 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 video games, or even reproduce full motion video. The widespread decision to support the Sound Blaster design in multimedia and entertainment titles meant that future sound cards such as Media Vision's Pro Audio Spectrum and the Gravis Ultrasound had to be Sound Blaster compatible if they were to sell well. Until the early 2000s, when the AC'97 audio standard became more widespread and eventually usurped the SoundBlaster as a standard due to its low cost and integration into many motherboards, Sound Blaster compatibility was a standard that many other sound cards supported to maintain compatibility with many games and applications released.