The input is line level only; so, unless you have an externally powered mic (or an old Apple PlainTalk mic) you probably aren't going to get any (or much) sound.
The Power Mac G5 has a stereo audio line-in jack on the back panel. The audio inputs are designed to accept high-level audio signals: 2.2 Vrms or +8 dbu, which is the standard output level from CD and DVD players. The output level of some consumer audio devices is lower, often 0.316 Vrms or ?10 dbV. Sound recordings made on the Power Mac G5 with such low-level devices have more noise than those made with high-level devices. The user may obtain better results by connecting an amplifier between the low-level device and the computer?s audio input jack.
The audio input jack is a 3.5 mm miniature phone jack with the signals connected as follows:
Tip: Left-channel audio
Ring: Right-channel audio
Sleeve: Audio ground
Based on a 1 kHz, 2VRMS sine wave input, 24-bit 44.1 kHz input format, 0 db input gain and no weighting, the line input has the following electrical characteristics :
maximum input voltage: 2.2 Vrms (+8 dBu)
input impedance: > 47 kilohms
bits per sample: 16-bit or 24-bit
channel separation: greater than 75 dB
frequency response: 20 Hz to 20 kHz, +0.5 dB/?3.0 dB
THD+N distortion: below < ?85 dB (no weighting)
If you want to use a generic microphone, you can get an adapter like the Griffin iMic.
Comments
A quote from Apple (PowerMac G5 Analog Audio Line-in)
The Power Mac G5 has a stereo audio line-in jack on the back panel. The audio inputs are designed to accept high-level audio signals: 2.2 Vrms or +8 dbu, which is the standard output level from CD and DVD players. The output level of some consumer audio devices is lower, often 0.316 Vrms or ?10 dbV. Sound recordings made on the Power Mac G5 with such low-level devices have more noise than those made with high-level devices. The user may obtain better results by connecting an amplifier between the low-level device and the computer?s audio input jack.
The audio input jack is a 3.5 mm miniature phone jack with the signals connected as follows:
Tip: Left-channel audio
Ring: Right-channel audio
Sleeve: Audio ground
Based on a 1 kHz, 2VRMS sine wave input, 24-bit 44.1 kHz input format, 0 db input gain and no weighting, the line input has the following electrical characteristics :
If you want to use a generic microphone, you can get an adapter like the Griffin iMic.