The Power Macintosh G3 is not configured as a typical AV style Power Macintosh in that it does not have RCA jacks for sound in and out, nor additional video in and out ports. Instead, it relies on external FireWire devices for providing advanced audio/video capabilites.
Here are the details relating to the sound capabilities of the Power Macintosh G3 logic board:
Sound System
The sound system for the Power Macintosh G3 computer supports 44.1 kHz 16-bit stereo sound output and input, available simultaneously.
Like other AV class Macintosh computers, the sound circuitry and system software can create sounds digitally and either play the sounds through the speaker inside the enclosure or send the sound signals out through the sound output jack. The Power Macintosh G3 computer also records sound from several sources: an analog sound source connected to the line-level sound input jack, analog sound from the modem card connected to the internal modem connector, or a compact disc in the CD-ROM player. With each sound input source, sound playthrough can be enabled or disabled.
Sound Output
The Power Macintosh G3 computer provides one 3.5-mm mini jack for sound output on the back of the enclosure. The output jack is connected to the sound amplifier; the mini jack is intended for connecting a pair of headphones or amplified external speakers. Inserting a plug into the sound output mini jack disconnects the internal speaker. The enclosure has one built-in speaker.
The Burgundy IC provides the stereo sound output to both the internal speakers and the sound output jack. The sound output jack has the following electrical characteristics:
* output sound signal to noise ratio (SNR) <90 dB unweighted (typical) when sound playback is from system hard disk or main memory .
* output sound SNR <80 dB unweighted (nominal) when playback is from CD .
* overall output sound SNR <90 dB unweighted (typical).
Sound Input
The Power Macintosh G3 computer provides a stereo sound input jack on the back of the enclosure for connecting an external PlainTalk microphone or other sound source. The sound input jack accepts a standard 3.5-mm stereophonic phone plug (two signals plus ground).
Note:
The Apple PlainTalk microphone requires power from the main computer, which it obtains by way of an extra-long, 4-conductor plug that makes contact with a 5-volt pin inside the sound input jack.
The sound input jack has the following electrical characteristics:
* input impedance: 20 kW
* maximum input level without distortion: 2.5 V peak to peak (Vpp) maximum
* line-level microphone voltage range of 0.28 V to 2.1 V peak to peak
* input SNR <90 dB unweighted (typical) for recording to system hard disk drive or system main memory
Digitizing Sound
The sound circuitry digitizes and records sound as 44.1 kHz 16-bit samples. If a sound sampled at a lower rate on another computer is played as output, the Sound Manager transparently upsamples the sound to 44.1 kHz prior to outputting the audio to the Burgundy sound IC.
The preferred sound sampling rate for output is specified in the Monitors and Sound control panel when the sound input is not in use. The preferred output sampling rate is overridden by the setting of the input sampling rate, because the input and output sampling rates are physically locked together. The sound output sampling rate is always 44.1 kHz.
When recording sound from a microphone, applications that are concerned about feedback should disable sound playthrough by calling the Sound Manager APIs.
The Burgundy IC provides separate sound buffers for input and for stereo output so that the computer can record and send digitized sound to the sound outputs simultaneously.