| A sound card is a computer expansion card that can | | | | of sounds that can be played back simultaneously and |
| input and output sound under control of computer | | | | independently) and the number of channels (intended |
| programs. Typical uses of sound cards include | | | | as the number of distinct electrical audio outputs). |
| providing the audio component for multimedia | | | | For example, many older sound chips had three voices, |
| applications such as music composition, editing video or | | | | but only one audio channel (mono) where all the voices |
| audio, presentation/education, and entertainment | | | | were mixed into, while the AdLib sound card had 9 |
| (games). Many computers have sound capabilities built | | | | voice and 1 mono channel. |
| in, while others require these expansion cards if audio | | | | For a number of years, most PC sound cards had |
| capability is desired. | | | | multiple FM synthesis voices (typically 9 or 18) which |
| A typical sound card includes a sound chip, usually | | | | were mostly used for MIDI music, but only one (mono) |
| featuring a digital-to-analog converter, that converts | | | | or two(stereo) voice(s) and channel(s) dedicated to |
| recorded or generated digital waveforms of sound into | | | | playing back digital sound samples, and playing back |
| an analog format. This signal is led to a (typically 1 | | | | more than one digital sound sample required |
| 8-inch earphone-type) connector where an amplifier, | | | | performing a software downmix at a fixed sampling |
| headphones, or similar sound destination can be | | | | rate. Modern low-cost integrated soundcards using an |
| plugged in. More advanced designs usually include | | | | audio codec like the AC'97 still work that way, although |
| more than one sound chip to separate duties between | | | | they may have more than two sound output channels |
| digital sound production and synthesized sounds | | | | (surround sound). |
| (usually for real-time generation of music and sound | | | | Today, a sound card having hardware support for |
| effects utilizing little data and CPU time). | | | | more than the two standard stereo voices, is likely to |
| Digital sound reproduction is usually achieved by | | | | referred at as "providing hardware audio acceleration". |
| multi-channel DACs, able to play multiple digital samples | | | | In 1984, the IBM PCjr debuted with a rudimentary |
| at different pitches and volumes, optionally applying | | | | 3-voice sound synthesis chip, the SN76489, capable of |
| real-time effects like filtering or distortion. Multi-channel | | | | generating three square-wave tones with variable |
| digital sound playback can also be used for music | | | | amplitude, and a pseudo white noise channel that could |
| synthesis if used with a digitized instrument bank of | | | | generate primitive percussion sounds. The Tandy 1000, |
| some sort, typically a small amount of ROM or Flash | | | | initially being a clone of the PCjr, duplicated this |
| memory containing samples corresponding to the | | | | functionality, with the Tandy TL/SL/RL line adding digital |
| standard MIDI instruments. (A contrasting way to | | | | sound recording/playback capabilities. |
| synthesize sound on a PC uses "audio codecs", which | | | | In the late 1990s, many computer manufacturers |
| rely heavily on software for music synthesis, MIDI | | | | began to replace plug-in soundcards with a "codec" |
| compliance and even multiple-channel emulation. This | | | | (actually a combined audio AD/DA-converter) |
| approach has become common as manufacturers | | | | integrated into the motherboard. Many of these used |
| seek to simplify the design and the cost of the sound | | | | Intel's AC97 specification. Others used cheap ACR |
| card itself). | | | | slots. |
| Most sound cards have a line in connector where the | | | | As of 2005, these "codecs" usually lack the hardware |
| sound signal from a cassette tape recorder or similar | | | | for direct music synthesis or even multi-channel sound, |
| sound source can be input. The sound card can digitize | | | | with special drivers and software making up for these |
| this signal and store it (controlled by the corresponding | | | | lacks, at the expense of CPU speed (for example, |
| computer software) on the computer's hard disk for | | | | MIDI reproduction takes away 10-15% CPU time on an |
| editing or further reproduction. Another typical external | | | | Athlon XP 1600+ CPU). |
| connector is the microphone connector, for connecting | | | | Nevertheless, some manufacturers offered (and offer, |
| to a microphone or other input device that generates a | | | | as of 2006) motherboards with integrated "real" |
| relatively lower voltage than the line in connector. Input | | | | (non-codec) soundcards usually in the form of a |
| through a microphone jack is typically used by speech | | | | custom chipset providing e.g. full ISA or PCI |
| recognition software or Voice over IP applications. | | | | Soundblaster compatibility, thus saving an expansion |
| Another important characteristic of any sound card is | | | | slot while providing the user with a (relatively) high |
| the number of distinct voices (intended as the number | | | | quality soundcard. |