The sound circuitry, called Tumbler, is connected to the KeyLargo IC by a standard I2S bus. The KeyLargo IC provides DB-DMA (descriptor-based direct memory access) support for the I2S port.
The Tumbler circuitry includes a signal processing IC that handles the equalization and volume control functions, a codec IC that performs A-to-D and D-to-A conversion, and a digital power amplifier that drives the Apple speaker minijack.
All audio is handled digitally inside the computer. The Tumbler circuitry performs digital-to-analog conversion for the audio signals to the internal speaker and the headphone jack.
For a description of the features of the sound system, see "Sound System".