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| Sound Card |
A Sound Blaster Live! Value card, a typical (circa 2000) PCI sound card. |
Connects to:
- Motherboard via one of
- Line in or out: via one of
- Microphone via one of
- TRS connector
- DIN connector
|
| Common Manufacturers:
|
A sound card (also known as an audio card) is a computer expansion card that facilitates the input and output of audio signals to/from a computer under control of computer programs. 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).
Many computers have sound capabilities built in, while others require additional expansion cards to provide for audio capability.
[edit] General characteristics
Sound cards usually feature a digital-to-analog converter, that 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 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, or an auxiliary backplate. More advanced cards usually include more than one sound chip to provide for
higher data rates and multiple simultaneous functionality, eg between digital sound production and 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 multiple digital samples simultaneously at different pitches and volumes, or optionally applying real-time
effects like filtering or distortion. Multi-channel digital sound playback can also be used for music synthesis when used
with a digitized instrument bank, typically a small amount of ROM or Flash memory containing samples corresponding to MIDI instruments. A contrasting way to synthesize sound on a PC uses "audio codecs", which rely heavily on software for music synthesis, MIDI compliance, and even multiple-channel emulation. This approach has become common as manufacturers
seek to simplify the design and the cost of sound cards.
Most sound cards have a line in connector for signal from a cassette tape recorder or similar sound source. The sound card digitizes this signal and stores it (under control of appropriate matching
computer software) on the computer's hard disk for storage, editing, or further processing. Another common external connector is the microphone connector, for use
by a microphone or other low level input device. Input through a microphone jack is often used by speech recognition software or for Voice over IP applications.
[edit] Sound channels and polyphony
Another important characteristic of sound cards is polyphony, which is more than one distinct voice or sound playable simultaneously and independently, and the number of
simultaneous channels. These are intended as the number of distinct electrical audio outputs, which may correspond
to a speaker configuration such as 2.0 (stereo), 2.1 (stereo and sub woofer), 5.1 etc.). Sometimes, the terms "voices" and
"channels" are used interchangeably to indicate the degree of polyphony, not the output speaker configuration.
For example, many older sound chips could accommodate three voices, but only one audio channel (ie, a single mono output) for output, requiring all voices to
be mixed together. More recent cards, such as the AdLib sound card, have a 9 voice polyphony and 1 mono channel as a combined output.
For some years, most PC sound cards have had multiple FM synthesis voices (typically 9 or 16) which were usually used for
MIDI music. The full capabilities of advanced cards aren't often completely 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 soundcards (ie, those built into motherboards) such as audio codecs like those meeting the AC'97 standard and even some budget expansion soundcards still work that way. They 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, these tasks are performed
entirely in software. This is similar to the way inexpensive softmodems perform modem tasks in software rather than in hardware).
Also, in the early days of wavetable synthesis, some sound card manufacturer advertises polyphony solely on the MIDI capabilities
alone. In this case, the card's output channel is irrelevant (and typically, the card is only capable of two channels of digital
sound). Instead, the polyphony measurement solely applies to the amount of MIDI notes the sound card is capable of producing
at one given time.
Today, a sound card providing actual hardware polyphony, regardless of the number of output channels, is typically referred
to as a "hardware audio accelerator", although actual voice polyphony is not the sole (or even a necessary) prerequisite,
with other aspects such as hardware acceleration of 3D sound, positional audio and real-time DSP effects being more important.
Since digital sound playback has become available and provided better performance than synthesis, modern soundcards with
hardware polyphony don't actually use DACs with as many channels as voices, but rather perform voice mixing and effects processing
in hardware (eventually performing digital filtering and conversions to and from the frequency domain for applying certain
effects) inside a dedicated DSP. The final playback stage is performed by an external (in reference to the DSP chip(s)) DAC
with significantly fewer channels than voices (e.g., 8 channels for 7.1 audio, which can be divided among 32, 64 or even 128
voices).
[edit] History of sound cards for the IBM PC architecture
The
AdLib Music Synthesizer Card, was one of the first sound cards circa 1987
Sound cards for computers compatible with the IBM PC were uncommon until 1988, which left the single internal PC speaker as the only way early PC software could produce sound and music. The speaker hardware was typically limited to square waves,
which fit the common nickname of "beeper". The resulting sound was generally described as "beeps and boops". Several companies,
most notably Access Software, developed techniques for digital sound reproduction over the PC speaker; the resulting audio, while baldly functional, suffered
from distorted output and low volume, and usually required all other processing to be stopped while sounds were played. Other
home computer models of the 1980s included hardware support for digital sound playback, or music synthesis (or both), leaving
the IBM PC at a disadvantage to them when it came to multimedia applications such as music composition or gaming.
It is important to note that the initial design and marketing focuses of sound cards for the IBM PC platform were not based
on gaming, but rather on specific audio applications such as music composition (AdLib Personal Music System, Creative Music System, IBM Music Feature Card) or on speech synthesis (Digispeech DS201, Covox Speech Thing, Street Electronics Echo). Only until Sierra and other game companies became involved in 1988 was there a switch toward
gaming.
[edit] Hardware manufacturers
One of the first manufacturers of sound cards for the IBM PC was AdLib, who produced a card based on the Yamaha YM3812 sound chip, aka the OPL2. The AdLib had two modes: A 9-voice mode where each voice could be fully programmed, and a less
frequently used "percussion" mode with 3 regular voices producing 5 independent percussion-only voices for a total of 11.
(The percussion mode was considered inflexible by most developers; it was used mostly by AdLib's own composition software.)
Creative Labs also marketed a sound card about the same time called the Creative Music System. Although the C/MS had twelve voices to AdLib's nine, and was a stereo card while the AdLib was mono, the basic technology
behind it was based on the Philips SAA 1099 chip which was essentially a square-wave generator. It sounded much like twelve simultaneous PC speakers would have, and
failed to sell well, even after Creative renamed it the Game Blaster a year later, and marketed it through Radio Shack in
the US. The Game Blaster retailed for under $100 and included the hit game Silpheed.
A large change in the IBM PC compatible sound card market happened with Creative Labs' introduced the Sound Blaster card. The Sound Blaster cloned the AdLib, and added a sound coprocessor for recording and play back of digital audio
(likely to have been an Intel microcontroller relabeled by Creative). It was incorrectly called a "DSP" to suggest it was a digital signal processor), a game port for adding a joystick, and capability to interface to MIDI equipment (using the game port and a special cable). With more features at nearly the
same price, and compatibility as well, most buyers chose the Sound Blaster. It eventually outsold the AdLib and dominated
the market.
The Sound Blaster line of cards, together with the first inexpensive CD-ROM drives and evolving video technology, ushered in a new era of multimedia computer applications that could play back CD audio, add recorded dialogue to computer games, or even reproduce motion video (albeit at much lower resolutions and quality in early days). The widespread decision to
support the Sound Blaster design in multimedia and entertainment titles meant that future sound cards such as Media Vision's Pro Audio Spectrum and the Gravis Ultrasound had to be Sound Blaster compatible if they were to sell well. Until the early 2000s (by which the AC'97 audio standard became more widespread and eventually
usurped the SoundBlaster as a standard due to its low cost and integration into many motherboards), Sound Blaster compatibility
is a standard that many other sound cards still support to maintain compatibility with many games and applications released.
[edit] Industry adoption
When game company Sierra On-Line opted to support add-on music hardware (instead of built-in hardware such as the PC speaker and built-in sound capabilities of the IBM PCjr and Tandy 1000), what could be done with sound and music on the IBM PC changed dramatically. Two of the companies Sierra partnered with
were Roland and Adlib, opting to produce in-game music for King's Quest 4 that supported the Roland MT-32 and Adlib Music Synthesizer. The MT-32 had superior output quality, due in part to its method of sound synthesis as well as built-in reverb. Since it
was the most sophisticated synthesizer they supported, Sierra chose to use most of the MT-32's custom features and unconventional
instrument patches, producing background sound effects (eg, chirping birds, clopping horse hooves, etc.) before the Sound
Blaster brought playing real audio clips to the PC entertainment world. Many game companies also supported the MT-32, but
supported the Adlib card as an alternative because of the latter's higher market base. The adoption of the MT-32 led the way
for the creation of the MPU-401/Roland Sound Canvas and General MIDI standards as the most common means of playing in-game music until the mid-1990s.
[edit] Feature evolution
Early ISA bus soundcards were half-duplex, meaning they could not record and play digitized sound simultaneously, mostly due to inferior
card hardware (eg, DSPs). Later, ISA cards like the SoundBlaster AWE series and Plug-and-play Soundblaster 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 soundcards 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.
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 in relative to the earlier OPL-based solutions, which uses FM-synthesis. Also,
some higher end cards started having it's 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 Gravis Ultrasound 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,
soundcard companies would also sometimes boast about the card's polyphony capabilities in terms of MIDI synthesis. In this
case polyphony solely refers to the amount of MIDI notes the card is capable of synthesizing simultaneously at one given time
and not the amount 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 90s, and quadraphonic sound came in the late 90s. This was shortly followed
by 5.1 channel audio. The latest soundcards support up to 8 physical audio channels in the 7.1 speaker setup.
[edit] Professional soundcards (audio interfaces)
Professional soundcards are special soundcards optimized for real time (or at least low latency) multichannel sound recording
and playback, including studio-grade fidelity. Their drivers usually follow the ASIO protocol for use with professional sound engineering and music software, although ASIO drivers are also available for a range
of consumer-grade soundcards.
Professional soundcards are usually described as "audio interfaces", and sometimes have the form of external rack-mountable
units using USB 2.0, Firewire, or an optical interface, to offer sufficient data rates. The emphasis in these products is, in general, on multiple input
and output connectors, direct hardware support for multiple input and output sound channels, as well as higher sampling rates
and fidelity as compared to the usual consumer soundcard. In that respect, their role and intended purpose is more similar
to a specialized multi-channel data recorder and real-time audio mixer and processor, roles which are possible only to a limited
degree with typical consumer soundcards.
On the other hand, certain features of consumer soundcards such as support for EAX, optimization for hardware acceleration in video games, or real-time ambience effects are secondary in professional soundcards, nonexistent or even undesirable on professional
soundcards, and as such audio interfaces are not recommended for the typical home user.
The typical "consumer-grade" soundcard is intended for generic home, office, and entertainment purposes with an emphasis
on playback and casual use, rather than catering to the needs of audio professionals. In response to this, Steinberg (the creators of audio recording and sequencing software, Cubase and Nuendo) developed a protocol that specified the handling of multiple audio inputs and outputs.
In general, consumer grade soundcards impose several restrictions and inconvenieces that would be unacceptable to an audio
professional. One of a modern soundcard's purposes is to provide an AD/DA converter (Analog to Digital/Digital to Analog).
However, in professional applications, there is usually a need for enhanced recording or Analog to Digital conversion capabilities.
One of the limitations of consumer soundcards is their comparatively large sampling latency; this is the time it takes
for the AD Converter to complete conversion of a sound sample and transfer it to the computer's main memory.
Consumer soundcards are also limited in the effective sampling rates and bit depths they can actually manage (compare
Analog sound vs. digital sound and have lower numbers of less flexible input channels: professional studio recording use typically requires more than two
channels which consumer soundcards provide, and more accessible connectors, unlike the variable mixture of internal -- and
sometimes virtual -- and external connectors found in consumer-grade soundcards.llll
[edit] Sound devices other than expansion cards
[edit] Integrated sound hardware on PC motherboards
In 1984, the first IBM PCjr had only a rudimentary 3-voice sound synthesis chip (the SN76489) which was capable of generating three square-wave tones with variable amplitude, and a pseudo white noise channel that could generate primitive percussion sounds. The Tandy 1000, initially a clone of the PCjr, duplicated this functionality, with the Tandy TL/SL/RL models adding digital sound recording/playback
capabilities.
In the late 1990s, many computer manufacturers began to replace plug-in soundcards with a "codec" chip (actually a combined audio AD/DA-converter) integrated into the motherboard. Many of these used Intel's AC97 specification. Others used inexpensive ACR slot accessory cards.
As of 2005, these "codecs" usually lack the hardware for direct music synthesis or even multi-channel sound, with special
drivers and software making up for these lacks, at the expense of CPU speed (for example, MIDI reproduction takes away 10-15%
CPU time on an Athlon XP 1600+ CPU).
Nevertheless, some manufacturers offered (and offer, as of 2006) motherboards with integrated "real" (non-codec) soundcards,
usually in the form of a custom chipset providing something akin to full ISA or PCI Soundblaster compatibility; this saves an expansion slot while providing the user with a (relatively) high quality soundcard.
[edit] Integrated sound on other platforms
Various non-IBM PC compatible computers, such as early home computers like the Commodore C64 and Amiga or Apple's Macintosh, and workstations from manufacturers like Sun have had their own motherboard integrated sound devices. In some cases, most notably in those of the Commodore Amiga and the C64, they provide very advanced capabilities (as of the time of manufacture), in others they are only minimal capabilities. Some
of these platforms have also had sound cards designed for their bus architectures which of course cannot be used in a standard PC.
The custom sound chip on Amiga, named Paula, had four digital sound channels (2 for the left speaker and 2 for the right) with 8 bit resolution (although
with patches, 14/15bit was accomplishable at the cost of high CPU usage) for each channel and a 6 bit volume control per channel.
Sound Play back on Amiga was done by reading directly from the chip-RAM without using the main CPU.
The quality of the Amiga's sound output is considered advanced in retrospect, because of the output capability which was
ahead of its time.
[edit] Sound cards on other platforms
While many of Apple's machines come with on-board sound capabilities, their bestselling Apple II suffered from a lack of
more than minimal sound devices, using only a beeper like the PC. To get around the problem, the Sweet Micro Systems company
developed the Mockingboard (a name-play on mockingbird), which was essentially a sound card for the Apple II. Early Mockingboard models ranged from 3 voices in mono, while some
later designs were 6 voices in stereo. Some software supported use of two Mockingboard cards which allowed 12 voice music and sound. A 12 voice, single card clone of the Mockingboard called the Phasor was also made by Applied Engineering. In late 2005 a company called ReactiveMicro.com produced a 6 voice clone called the Mockingboard v1 and also has plans to clone the Phasor and produce a hybrid card which
will be user selectable between Mockingboard and Phasor modes plus support both the SC-01 or SC-02 speech synthesizers.
[edit] USB sound "cards"
USB sound "cards" are actually external boxes that plug into the computer via USB.
The USB specification defines a standard interface, the USB audio device class, allowing a single driver to work with the various USB sound devices on the market. Cards meeting the USB 2.0 specification
have sufficient data transfer capacity to support high quality sound operation if their circuit design permits.
[edit] Other outboard sound devices
USB Sound Cards are far from the first external devices allowing a computer to record or synthesize sound. For example,
devices such as the Covox Speech Thing were attached to the parallel port of an IBM PC and fed 6- or 8-bit PCM sample data to produce audio. Also, many types of
professional soundcards (audio interfaces) have the form of an external Firewire or USB unit, usually for convenience and
improved fidelity.
Soundcards using the PCMCIA cardbus interface were popular in the early days of portable computing when laptops and notebooks
did not have onboard sound. Even today, while rare, these cardbus audio solutions are still used in some setups in which the
onboard sound solution of the notebook or laptop is not up to par with the owners' expectations or requirements, and are particularly
targeted at mobile DJs, with units providing separated outputs usually allow both playback and monitoring from one system.
[edit] Driver architecture
To use a sound card, the operating system typically requires a specific device driver. This is a low-level program that handles the data connections between the physical hardware and the operating system. Some operating systems include the drivers for some or all cards available, in other cases the drivers are supplied with
the card itself, or are available for download.
- DOS programs for the IBM PC often had to use universal middleware driver libraries (such as the HMI Sound Operating System, the Miles Audio Interface Libraries (AIL), the Miles Sound System etc.) which had drivers for most common sound cards, since DOS itself had no real concept of a sound card. Some card manufacturers
provided (sometimes inefficient) middleware TSR-based drivers for their products, and some programs simply had driver/middleware source code incorporated into the program
itself for the sound cards that were supported.
- Microsoft Windows uses proprietary drivers generally written by the sound card manufacturers. Many makers supply the drivers to Microsoft for inclusion on Windows
distributions. Sometimes drivers are also supplied by the individual vendors for download and installation. Bug fixes and
other improvements are likely to be available faster via downloading, since Windows CDs cannot be updated as frequently as
a web or FTP site. Vista uses UAA.
- A number of versions of UNIX make use of the portable Open Sound System (OSS). Drivers are seldom produced by the card manufacturer.
- Most present day Linux-based distributions make use of the Advanced Linux Sound Architecture (ALSA). Up until Linux kernel 2.4, OSS was the standard sound architecture for Linux, although ALSA can be downloaded, compiled
and installed separately for kernels 2.2 or higher). But from kernel 2.5 onwards, ALSA was integrated into the kernel and
the OSS native drivers were deprecated. Backwards compatibility with OSS-based software is maintained, however, by the use
of the ALSA-OSS compatibility API and the OSS-emulation kernel modules.
- Mockingboard support on the Apple II is usually incorporated into the programs itself as many programs for the Apple II
boots directly from disk.
