Sound card mixer
Control channels Controlled source
Wave / PCM stereo Audio signal generated by the CPU via the sound card 's digital-to-analog converter . ( This includes audio produced by games , MP3 or WAV players , but also some software playing a CD-DA through the CPU , such as , Windows Media Player or Media Player Classic , as well as TV tuner cards that use the CPU for decoding audio . )
MIDI/SW Synth stereo Audio signal generated by a synthesizer chip ( often described as MIDI device ) or digital signal processor on the sound card
CD playback stereo Audio signal received from the analog CD input of the mixer , which is usually connected to the analog audio output of a CD drive
Microphone mono Audio signal received through one of the ( typically two : MIC1 and MIC2 , switchable ) analog microphone inputs . MIC1 is typically connected to the external microphone jack ( colored pink under PC99 ) . An optional 20 decibel ( 10× voltage ) amplifier can be activated for this input in most mixers
Line in stereo Audio signal received through the LINE input of the mixer , usually connected to an external jack ( colored light blue in PC99 ) , which can be used to connect a HiFi amplifier , tuner , iPod , television , etc
Aux in stereo Audio signal received through the AUX input of the mixer . This mixer input is not used by all PCs
PC speaker mono Some sound cards provide an input for the ( very crude ) audio signal that the Programmable Interval Timer of an IBM PC generates for the PC speaker
SPDIF stereo Digital interface , uncommon in the PC world
Typical input channels and controls
A sound card mixer is the analog part of a sound card that routes and mixes sound signals. This circuit receives inputs from both external connectors and the sound card's digital-to-analog converters. It selects or mutes, amplifies (with variable gain) these signals, adds them together, and finally routes the result to both external output connectors and the sound card's analog-to-digital converters. Different mixing schemes are in use, but the ones implemented in most IBM-PC compatible computers today are variants of a scheme defined in Intel's AC'97 Audio Component Specification.