The output signal is connected to an amplifier, headphones, or external device using standard interconnects, such as a TRS phone connector.

Early PC sound cards had multiple FM synthesis voices (typically 9 or 16) which were used for MIDI music.

In the early days of wavetable synthesis, some sound card manufacturers advertised polyphony solely on the MIDI capabilities alone.

Several companies, most notably Access Software, developed techniques for digital sound reproduction over the PC speaker like RealSound.

The resulting audio, while functional, suffered from the heavily distorted output and low volume, and usually required all other processing to be stopped while sounds were played.

Other home computers of the 1980s like the Commodore 64 included hardware support for digital sound playback or music synthesis, leaving the IBM PC at a disadvantage when it came to multimedia applications.

In 1988, a panel of computer-game CEOs stated at the Consumer Electronics Show that the PC's limited sound capability prevented it from becoming the leading home computer, that it needed a $49–79 sound card with better capability than current products, and that once such hardware was widely installed, their companies would support it.

It sounded much like twelve simultaneous PC speakers would have except for each channel having amplitude control, and failed to sell well, even after Creative renamed it the Game Blaster a year later, and marketed it through RadioShack in the US.

"[8] The magazine that year stated that Wing Commander II was "Probably the game responsible" for making it the standard card.

When game company Sierra On-Line opted to support add-on music hardware in addition to 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.

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 (e.g., chirping birds, clopping horse hooves, etc.)

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.

Sound cards have evolved in terms of digital audio sampling rate (starting from 8-bit 11025 Hz, to 32-bit, 192 kHz that the latest solutions support).

introduced their own RAM and processor for user-definable sound samples and MIDI instruments as well as to offload audio processing from the CPU.

Even today, the tendency is still to mix multiple sound streams in software, except in products specifically intended for gamers or professional musicians.

According to Microsoft, the functionality was hidden by default in Windows Vista to reduce user confusion, but is still available, as long as the underlying sound card drivers and hardware support it.

[12] A few early sound cards had sufficient power to drive unpowered speakers directly – for example, two watts per channel.

With the popularity of amplified speakers, sound cards no longer have a power stage, though in many cases they can adequately drive headphones.

Their drivers usually follow the Audio Stream Input/Output protocol for use with professional sound engineering and music software.

Consumer sound cards are also limited in the effective sampling rates and bit depths they can actually manage and have lower numbers of less flexible input channels.

However, these features were dropped when AC'97 was superseded by Intel's HD Audio standard, which was released in 2004, again specified the use of a codec chip, and slowly gained acceptance.

By 1989, the FM Towns computer platform featured built-in PCM sample-based sound and supported the CD-ROM format.

The T-Unit hardware already has an onboard YM2151 OPL chip coupled with an OKI 6295 DAC, but said game uses an added-on DCS card instead.

[17] The card is also used in the arcade version of Midway and Aerosmith's Revolution X for complex looping music and speech playback.

Sound cards were made for the C-Bus expansion slots that these computers had, most of which used Yamaha's FM and PSG chips and made by NEC themselves, although aftermarket clones can also be purchased, and Creative did release a C-Bus version of the SoundBlaster line of sound cards for the platform.

Devices such as the Covox Speech Thing could be 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 sound cards take the form of an external FireWire or USB unit, usually for convenience and improved fidelity.

DJ sound cards sometimes have inputs with phono preamplifiers to allow turntables to be connected to the computer to control the software's playback of music files with vinyl emulation.

The main function of a sound card is to play audio, usually music, with varying formats (monophonic, stereophonic, various multiple speaker setups) and degrees of control.

Sound cards have been used to analyze and generate the following types of signals: To use a sound card, the operating system (OS) typically requires a specific device driver, a low-level program that handles the data connections between the physical hardware and the operating system.