Sound cards may include any or all of the following: Sound Synthesis hardware of several kinds; MIDI input/output; an audio mixer; Speaker or Microphone jacks; Analog to digital conversion; a gameport (joystick); IDE and/or proprietary CDROM digital controllers; and/or CD audio connections.
Several technologies are used to produce sounds:
FM Synthesis synthesizes sine waves (pure tones) and various frequencies and amplitudes and combines them. While it is theoretically possible to create any sound from the proper combination of sine waves, FM sound is generally thought to be of poor quality.
WaveTable sound combines digitally recorded sounds of various types to create complex sounds. Wavetables can vary in resolution and other parameters. The number of "voices" available in the sound card hardware also is related to sound quality.
MIDI is specifically directed at music and allows simulation of instruments.
Early software APIs offered little capability for controlling sound. Most sound control other than the simple canned Windows sounds was implemented by direct control of the sound hardware. It is not at all uncommon for a specific piece of software to refuse to play sounds with a given sound card. Most sound cards advertise some capability to emulate the Creative Labs Soundblaster cards. Older software will expect the 8 bit version, newer programs the 16 bit version.
Many sound cards require several DMA channels and IRQs to support the multiple built in interfaces. Sound cards are more likely to be ISA bus rather than PCI although PCI cards do exist.
Starting in 1997, Microsoft released a Direct-X API defining much expanded multimedia capability including some amount of generalized sound capability. Direct-X is intended to allow the programmer to simply specify what is desired and let the operating system determine what mix of hardware and software is required to create it.
Return To Index Copyright 1994-2002 by Donald Kenney.