Apple PowerBook G3 - Manual (Page 46)

IMPORTANT Although the internal microphone is deactivated when an
external sound input device is in use, it’s possible to record sound from more
than one sound device at the same time. This can occur because the computer
merges sound from devices in the expansion bay, such as an audio CD, with
sound from the PC Card slots, such as a television tuner card, and from the
internal expansion card slot (called PCI). If two or more devices in these
locations produce sound, the sound from all of the devices may be recorded
when you use the SimpleSound program or the Monitors & Sound control
panel to record. To eliminate the sounds you don’t want to record, remove or
turn off the device producing those sounds.
The Macintosh PowerBook also has a stereo sound output port (on the left
side of the computer’s case, marked with the - icon) to which you can
connect externally powered speakers, an amplifier, headphones, or other
audio output devices. The sound output port accepts a standard stereo
miniplug, like that used to attach headphones to a portable tape player.
Your computer also has four stereo speakers, which play sound from an audio
CD in the CD-ROM drive, from an external stereo device connected to the
computer through the sound input port, from a Zoomed Video card in the
lower PC Card slot, or from a file on your hard disk.
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Sound input port
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