Specifications

If audio data sampled from another computer at a lower rate is played as output on the Power Mac G5, the

Core Audio (Mac OS X’s OS Level Audio API) transparently up-samples the data to the currently set sampling

frequency prior to sending the audio data to the sound circuitry. To maximize audio fidelity, the Core Audio

samples are stored as 32-bit floating point. The Sound Manager exists as a Carbon compatibility layer, but

developers are encouraged to move their applications to Core Audio for maximum performance and fidelity,

because the Sound Manager is capable of representing samples only as 16-bit values.

For more information about audio API’s on Mac OS X, visit the Apple audio technologies developer web page

http://developer.apple.com/audio/

Optical Digital Audio

Digital data is transmitted to and from the digital audio I/O using optical cables. The physical connectors,

commonly referred to as TOSLink, are for both input and output and conform to IEC60874-17. The TOSLink

friction-lock type F-05 connectors are available from pro-audio, musician’s supply, hi-fi and other retailers. The

7.5 mm digital optical TOSLink input and output connectors, shown in Figure 3-5 (page 47), are located on

the back of the enclosure.

Figure 3-5 Optical digital S/PDIF connector

The digital I/O circuitry can either perform input clock recovery on an incoming data stream or can sample

using the internal clock. If samples are clocked using the internal clock, the data is run through the sample-rate

converter on the digital circuitry. To enable bit-accurate copies, the external clock should be enabled in Audio

MIDI Setup. Developers of applications that need this capability will need to provide access to the input clock

recovery control.

Audio signals from the audio input jack are converted to digital data internally. All audio is handled digitally

inside the computer, including audio data from the CD or DVD drive and from devices connected to the USB

and FireWire ports. Audio data is converted to analog form for output to the internal speaker, the headphones,

line output jacks, or external speakers.

For details on the optical digital input and output electrical specifications, refer to Optical Digital Input/Output

Specifications (page 48).

Input and Output Devices

Audio