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