Mac OS 9 introduces audio routing capabilities to accommodate digital audio devices such as USB speakers and microphones. Routing of the input audio signal to the current output audio devices introduces a small amount of latency. This happens only when "Play sound through output device" is selected for that input source in the Sound control panel.

Symptom

There is a slight delay in sound output. For example, if you are talking through a PlainTalk microphone and "Play sound through output device" is selected in the Sound control panel, your voice may sound like an echo coming through the speakers.

Products affected

• Mac OS 9
• iBook
• PowerBook (FireWire)
• Power Mac G4 (AGP Graphics)
• Power Mac G4 (Gigabit Ethernet)
• Power Mac G4 Cube
• iMac (Slot loading)
• iMac (Summer 2000) See Note.

Solution

Turn off "Play sound through output device" in the Sound control panel to eliminate this effect.

In most cases, playing the audio through to the speakers is not necessary. If you need to monitor the input source, monitor it at the source device (with a headphone jack) or with an audio mixer instead of using the computer's audio output.

Note: The parenthetical product description (Summer 2000) refers to the summer of the Northern Hemisphere.