Troubleshooting the Power Mac G5: Optical out issues

Optical out issues William Kucharski offers a technical explanation behind some of the optical audio out quirks we have been covering over the past week:

"Basically, most any D/A converter needs a few samples to lock onto the proper sampling rate and format for the data. For example, most speaker systems and D/A converters can handle PCM, Dolby Digital or DTS data streams at at least 44.1 and 48KHz.

"It usually takes a few samples for the converter to recognize the format and sampling rate it is receiving, with the end result that playback cannot occur until the converter has its first full frame for the audio format being transmitted.

"If the device sending the digital audio does not maintain a digital data stream at all times - regardless of whether audio is currently being sent or not - the D/A converter will have to go through the format detect cycle all over again.

"As you state, the ways to avoid this are either to have the digital out always send output, or to have the D/A converter "lock" the mode (for example, many home theatre D/A converters can be told that a signal is always, for example, a 48 KHz Dolby Digital signal, and then it won't drop a few samples determining the digital audio format.)"

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