What's inside your computer


The sound card

A sound card is a computer expansionAnother important characteristic of any
card that can input and output soundsound card is the number of distinct
under control of computer programs.voices (intended as the number of sounds
Typical uses of sound cards includethat can be played back simultaneously
providing the audio component forand independently) and the number of
multimedia applications such as musicchannels (intended as the number of
composition, editing video or audio,distinct electrical audio outputs).
presentation/education, andFor example, many older sound chips had
entertainment (games). Many computersthree voices, but only one audio channel
have sound capabilities built in, while(mono) where all the voices were mixed
others require these expansion cards ifinto, while the AdLib sound card had 9
audio capability is desired.voice and 1 mono channel.
A typical sound card includes a soundFor a number of years, most PC sound
chip, usually featuring acards had multiple FM synthesis voices
digital-to-analog converter, that(typically 9 or 18) which were mostly
converts recorded or generated digitalused for MIDI music, but only one (mono)
waveforms of sound into an analogor two(stereo) voice(s) and channel(s)
format. This signal is led to adedicated 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 destinationa software downmix at a fixed sampling
can be plugged in. More advanced designsrate. Modern low-cost integrated
usually include more than one sound chipsoundcards using an audio codec like the
to separate duties between digital soundAC'97 still work that way, although they
production and synthesized soundsmay have more than two sound output
(usually for real-time generation ofchannels (surround sound).
music and sound effects utilizing littleToday, a sound card having hardware
data and CPU time).support for more than the two standard
Digital sound reproduction is usuallystereo voices, is likely to referred at
achieved by multi-channel DACs, able toas "providing hardware audio
play multiple digital samples atacceleration".
different pitches and volumes,In 1984, the IBM PCjr debuted with a
optionally applying real-time effectsrudimentary 3-voice sound synthesis
like filtering or distortion.chip, the SN76489, capable of generating
Multi-channel digital sound playback canthree square-wave tones with variable
also be used for music synthesis if usedamplitude, and a pseudo white noise
with a digitized instrument bank of somechannel that could generate primitive
sort, typically a small amount of ROM orpercussion sounds. The Tandy 1000,
Flash memory containing samplesinitially being a clone of the PCjr,
corresponding to the standard MIDIduplicated this functionality, with the
instruments. (A contrasting way toTandy TL/SL/RL line adding digital sound
synthesize sound on a PC uses "audiorecording/playback capabilities.
codecs", which rely heavily on softwareIn the late 1990s, many computer
for music synthesis, MIDI compliance andmanufacturers began to replace plug-in
even multiple-channel emulation. Thissoundcards with a "codec" (actually a
approach has become common ascombined audio AD/DA-converter)
manufacturers seek to simplify theintegrated into the motherboard. Many of
design and the cost of the sound cardthese used Intel's AC97 specification.
itself).Others used cheap ACR slots.
Most sound cards have a line inAs of 2005, these "codecs" usually lack
connector where the sound signal from athe hardware for direct music synthesis
cassette tape recorder or similar soundor even multi-channel sound, with
source can be input. The sound card canspecial drivers and software making up
digitize this signal and store itfor these lacks, at the expense of CPU
(controlled by the correspondingspeed (for example, MIDI reproduction
computer software) on the computer'stakes away 10-15% CPU time on an Athlon
hard disk for editing or furtherXP 1600+ CPU).
reproduction. Another typical externalNevertheless, some manufacturers offered
connector is the microphone connector,(and offer, as of 2006) motherboards
for connecting to a microphone or otherwith integrated "real" (non-codec)
input device that generates a relativelysoundcards usually in the form of a
lower voltage than the line incustom chipset providing e.g. full ISA
connector. Input through a microphoneor PCI Soundblaster compatibility, thus
jack is typically used by speechsaving an expansion slot while providing
recognition software or Voice over IPthe user with a (relatively) high
applications.quality soundcard.



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