Yesterday we covered an issue with the optical-out jack on the Power Mac G5 where short sounds don't appear to get passed though the optical connection, but longer ones do. A MacFixIt reader notes that this may simply be a drawback of certain optical outputs:
"The sound dropout seems to be a drawback of the way optical links send data -- the exact same thing happens at the begining of a track on a CD being played with my Laserdisc player or DVD player, or at the layer break (when the audio stream breaks as well) on a DVD... The only way around this in the case of a computer would be to constantly send some data so the amp always sees an incoming signal to process. iTunes seems to do this, and maybe someone will come up with an app that plays silence (keeps the auiod output awake, really) to prevent this from happening."
We should note that this doesn't happen on all computers with optical audio outputs, so perhaps some sound cards handle this situation more gracefully than others (and than the G5's optical-out circuitry).
We also mentioned that the G5's volume control doesn't affect the optical output; this is normal behavior for digital audio output, as the data is generally being sent to an external DAC (digital-to-analog converter) for processing, and volume is controlled by the receiver or amplifier that is fed the analog signal. In this respect, an optical digital output is similar to a standard line-level output.