Description
A sound
card (also known as an audio card) is an internal computer expansion card that
facilitates the input and output of audio signals to and from a computer under control
of computer programs. The term sound
card is also applied to
external audio interfaces that use software to generate sound, as opposed to
using hardware inside the PC. Typical uses of sound cards include providing the
audio component for multimedia applications such as music composition, editing
video or audio, presentation, education and entertainment (games) and video projection.
Sound functionality can also be integrated onto
the motherboard,
using basically the same components as a plug-in card. The best plug-in cards,
which use better and more expensive components, can achieve higher quality than
integrated sound. The integrated sound system is often still referred to as a
"sound card".
Most sound cards use a digital-to-analog converter (DAC), which converts recorded or
generated digital 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 or an RCA connector.
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. More advanced cards
usually include more than one sound chip to support higher data rates and
multiple simultaneous functionality, for example digital production of synthesized sounds, usually for real-time
generation of music and sound effects using minimal data and CPU time.
Digital sound reproduction is usually done with
multi channel DACs, which are capable of simultaneous and digital samples at
different pitches and volumes, and application of real-time effects such as
filtering or deliberate distortion. Multichannel digital sound playback can
also be used for music synthesis, when used with a compliance, and even
multiple-channel emulation. This approach has become common as manufacturers
seek simpler and lower-cost sound cards.
Features
Early ISA bus
soundcards were half-duplex, meaning they couldn't record and play digitized
sound simultaneously, mostly due to inferior card hardware (e.g., DSPs). Later, ISA cards like the
SoundBlaster AWE series and Plug-and-play Sound blaster clones eventually became
full-duplex and supported simultaneous recording and playback, but at the
expense of using up two IRQ and DMA channels instead of one, making them no
different from having two half-duplex sound cards in terms of configuration.
Towards the end of the ISA bus' life, ISA sound cards started taking advantage
of IRQ sharing, thus reducing the IRQs needed to one, but still needed two DMA
channels. Many PCI bus cards do not have these
limitations and are mostly full-duplex. It should also be noted that many
modern PCI bus cards also do not require free DMA channels to operate.
Also, throughout the years, soundcards have
evolved in terms of digital audio sampling rate (starting from 8-bit 11 025 kHz,
to 32-bit,192 kHz that
the latest solutions support). Along the way, some cards started offering wavetable synthesis, which provides superior MIDI synthesis quality relative to the
earlier OPL-based
solutions, which uses FM-synthesis. Also, some higher end cards
started having their own RAM and processor for user-definable sound samples and
MIDI instruments as well as to offload audio
processing from the CPU.
For years, soundcards had only one or two
channels of digital sound (most notably the Sound Blaster series and their compatibles) with the
exception of the E-MU card family, which had hardware
support for up to 32 independent channels of digital audio. Early games and MOD-players
needing more channels than a card could support had to resort to mixing
multiple channels in software. Even today, the tendency is still to mix
multiple sound streams in software, except in products specifically intended
for gamers or professional musicians, with a sensible difference in price from
"software based" products. Also, in the early era of wavetable
synthesis, sound card companies would also sometimes boast about the card's
polyphony capabilities in terms of MIDI
synthesis. In this case polyphony solely refers to the count of MIDI notes the card is capable of synthesizing
simultaneously at one given time and not the count of digital audio streams the
card is capable of handling.
In regards to physical sound output, the number
of physical sound channels has also increased. The first soundcard solutions
were mono. Stereo sound was introduced in the early 1980s, and quadraphonic sound came in 1989. This was shortly
followed by channel audio. The latest sound cards support
up to 8
physical audio channels in
the speaker
setup.
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