PC Sound Card Jack Colors

When sound cards first arrived on the PC, the jacks were usually all one
color, typically black. This state of affairs remained in effect until "PC
99," a pseudo-standard collaborated on by Microsoft and Intel (and third in a
series of four "PC System Design Guide" standards which also included PC 97,
PC 98, and PC 2001) defined a de facto industry standard for sound card jack
colors. The basic jack colors go something like this:

Green: Audio out (front speakers)
Black: Audio out (rear speakers)
Pink: Microphone in
Blue: Line in
Yellow/Orange: Subwoofer out

On surround-sound sound cards, the difference between the green and the black
jacks is that the green is for the front speakers, while the black is for the
rear. On stereo sound cards with only one line-out jack, this jack may be
either color, although green seems to be preferred as it more explicitly
defines the jack as being an audio output. If a surround-sound sound card is
configured for regular stereo (2-speaker) output, the green and black jacks
are interchangeable.

The pink and blue jacks are both used as audio inputs for the sound card to
record with. The difference is that the pink jack is intended for use with an
unpowered microphone, while the blue jack is meant to take a line-level audio
input. In audio terms, then, the sound card will generally use a much
higher-gain amplifier for the microphone input, since most computer
microphones make such a weak signal (typically only a few millivolts) that
the recording would be virtually inaudible without significant amplification.
The blue line-level input, by contrast, will use a much lower-gain
amplifier--or, frequently, no amplifier at all, as it is designed to receive
an already-amplified signal produced by the output of powered audio
equipment, which typically produces a signal level of over 100 millivolts. At
best, plugging a line-level signal into the microphone jack is likely to
vastly overdrive the sound card's microphone amplifier, resulting in unusably
clipped recording; at worst, doing so may burn out the sound card altogether.
Also note that since most computer microphones are mono, the pink microphone
input is usually mono as well, while the blue line-in jack can typically
receive stereo audio.

In addition to these colors, some sound cards emboss (or print) symbols on
their mounting bracket representing the functions of these jacks for further
identification. Typically, the audio-out jacks are represented with a symbol
of a wave-shape with an arrow coming out of it (symbolizing sound waves
coming "out" of the card), the line-in jacks have a symbol of a wave with an
arrow pointing into it, and the microphone jack usually just has a small
picture of a microphone. However, the surfaces of the mounting brackets on PC
sound cards are so cramped for space that there is often no room for such
symbols. This is also the reason why PC sound cards have standardized on the
relatively tiny 1/8" (3.5 mm) jack size while most other professional audio
equipment uses 1/4" (6.35 mm) jacks or RCA jacks as a standard.