Editing Sound card (section)

==General characteristics==
[[File:Computer sound card01.JPEG|thumb|left|Close-up of a sound card [[Printed circuit board|PCB]], showing [[electrolytic capacitor]]s, [[Surface-mount technology|SMT]] [[capacitor]]s and [[resistor]]s, and a YAC512 two-channel 16-bit [[digital-to-analog converter|DAC]].<ref>{{citation |archive-url=https://web.archive.org/web/20131013045254/http://www.datasheetarchive.com/dlmain/Datasheets-6/DSA-104253.pdf |url=http://www.datasheetarchive.com/dlmain/Datasheets-6/DSA-104253.pdf |archive-date=2013-10-13 |url-status=dead |title=YAC512 |publisher=Yamaha}}</ref> The [[integrated circuit]] on the left is a 3403 single power supply quad [[operational amplifier]].]]

Sound cards use a [[digital-to-analog converter]] (DAC), which converts recorded or generated [[Digital signal (signal processing)|digital signal]] data into an [[Analog signal|analog]] format. The output signal is connected to an amplifier, headphones, or external device using standard interconnects, such as a [[TRS phone connector]].{{efn|If the number and size of connectors is too large for the space on the backplate, the connectors will be off-board, typically using a breakout box, an auxiliary backplate, or a panel mounted at the front.}}

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]] (ADC) to digitize this signal.

Some cards include a [[sound chip]] to support the production of [[synthesizer|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===
[[File:CirrusLogicCS4282-AB.jpg|thumb|right|250px|8-channel DAC [[Cirrus Logic]] '''CS4382''' placed on [[Sound Blaster X-Fi]] Fatal1ty]]

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 (stereo), 2.1 (stereo and sub woofer), 5.1 (surround), 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 chip]]s could accommodate three voices, but only one output [[audio channel]] (i.e., a single mono output), 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 (typically 9 or 16) which were used for MIDI music. The full capabilities of advanced cards are often not fully used; only one (mono) or two ([[stereo]]) voice(s) and channel(s) 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 (i.e., those built into motherboards) such as [[audio codec]]s 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 (typically 5.1 or 7.1 [[surround sound]]), but they usually have no actual hardware polyphony for either sound effects or MIDI reproduction{{snd}} these tasks are performed entirely in software. This is similar to the way inexpensive [[softmodem]]s 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.