The Power Mac G4 computer provides a stereo sound input jack on the back of the enclosure for connecting an external PlainTalk microphone or a line-level sound source. The sound input jack accepts a standard 3.5 mm stereophonic phone plug (two signals plus ground). The sound input jack has the following electrical characteristics:
input impedance: 20 k
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