مشاهده نسخه کامل
: Vahed
12-10-2007, 22:07
Computer sound cards are actually computer expansion cards that can input and output sound under control of specific computer programs. Typical uses of computer 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 built in sound capabilities, while others require these expansion cards if audio capability is desired.
Computer sound cards for the IBM based PCs were uncommon until 1988, leaving the internal PC speaker as the only way. Early PC software could produce sound and music. The speaker was limited to square wave production, leading to the common nickname of "beeper" and the resulting sound 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 functional, suffered from distorted output and low volume, and usually required all other processing to halt 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 when it came to multimedia applications such as music composition or gaming.
One of the first manufacturers of computer 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 lesser-used "percussion" mode that used 3 regular voices to produce 5 independent percussion-only voices for a total of 11.
(The percussion mode was considered inflexible by most developers, so it was used mostly by AdLib's own composition software.) Probably the most significant historical change in the history of computer sound cards came when Creative Labs produced the Sound Blaster card. The Sound Blaster cloned the AdLib, and also added a sound coprocessor to record and play back digital audio (presumably an Intel microcontroller, which Creative incorrectly called a "DSP" to suggest it was a digital signal processor), a game port for adding a joystick, and the ability to interface to MIDI equipment (using the game port and a special cable). With more features at nearly the same price point, and compatibility with existing AdLib titles, most first-time buyers chose the Sound Blaster. The Sound Blaster eventually outsold the AdLib and set the stage for dominating the market.
Most ISA bus computer sound cards are half-duplex, which means they could not record and play digitized sound simultaneously, mostly due to inferior card 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 just one. Many PCI bus computer sound cards do not have these limitations and are mostly full-duplex. Now a days, a new type of computer sound cards are avilable which use Universal Serial Bus (USB) to recieve data from the motherboard. While not literally sound cards (since they don't plug into slots inside of a computer, and usually are not card-shaped), these are devices called USB computer sound cards. These attach to a computer via USB cables. 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.
IT Articles 2007
Computer sound cards for the IBM based PCs were uncommon until 1988, leaving the internal PC speaker as the only way. Early PC software could produce sound and music. The speaker was limited to square wave production, leading to the common nickname of "beeper" and the resulting sound 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 functional, suffered from distorted output and low volume, and usually required all other processing to halt 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 when it came to multimedia applications such as music composition or gaming.
One of the first manufacturers of computer 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 lesser-used "percussion" mode that used 3 regular voices to produce 5 independent percussion-only voices for a total of 11.
(The percussion mode was considered inflexible by most developers, so it was used mostly by AdLib's own composition software.) Probably the most significant historical change in the history of computer sound cards came when Creative Labs produced the Sound Blaster card. The Sound Blaster cloned the AdLib, and also added a sound coprocessor to record and play back digital audio (presumably an Intel microcontroller, which Creative incorrectly called a "DSP" to suggest it was a digital signal processor), a game port for adding a joystick, and the ability to interface to MIDI equipment (using the game port and a special cable). With more features at nearly the same price point, and compatibility with existing AdLib titles, most first-time buyers chose the Sound Blaster. The Sound Blaster eventually outsold the AdLib and set the stage for dominating the market.
Most ISA bus computer sound cards are half-duplex, which means they could not record and play digitized sound simultaneously, mostly due to inferior card 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 just one. Many PCI bus computer sound cards do not have these limitations and are mostly full-duplex. Now a days, a new type of computer sound cards are avilable which use Universal Serial Bus (USB) to recieve data from the motherboard. While not literally sound cards (since they don't plug into slots inside of a computer, and usually are not card-shaped), these are devices called USB computer sound cards. These attach to a computer via USB cables. 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.
IT Articles 2007