Audio System: Notes

Both the RAH and RBP radios are on the PCI Bus system. The audio output signal from the radios, on these central amplifier systems, is fixed at one volume level (level 25 for RAH and 26 for RBP). The actual volume, fade, balance, and tone adjustments are managed via messages sent over the PCI Bus from the radio to the amplifier which changes its speaker outputs to the corresponding settings. The amplifiers will also adjust volume based on speed messages received over the bus from the PCM. This keeps the sound level essentially constant relative to the interior noise level at all driving speeds.

Both the 6-channel base amplifier and the 8-channel surround sound amplifier perform digital signal processing and contain unique equalization curves in their memory. The specific audio source determines how the amplifier equalizes the individual channel outputs. Separate EQ's are provided for AM radio, FM radio, Tape, CD, and DVD video. There is a sixth EQ "slot" available for a TBD future input source. Audio signal EQ selection is based on bus messages received from the radio and Navigation unit. For example, DVD video is equalized for viewing video in the second and third row seats. Hands-free audio is processed using the AM radio EQ. Navigation audio is processed based on the current audio source EQ. The amplifier allows audio inputs from navigation and hands-free module to override whatever else might be playing at the time. The amplifier provides an independent output channels to each speaker location: 1) left front door, 2) right front door, 3) I/P center, 4) right rear door and 5) left rear door. On eight channel systems the amplifier provides two output (6 and 7) to a dual voice coil subwoofer. Both amplifiers contain diagnostic software allowing them to display Diagnostic Trouble Codes (DTCs) and perform certain diagnostic tests using the DRBIII®.

The tests available are the:

• Input Test - monitors input sources.
• PCI Amplifier Test - detect a checksum failure
• Identify EQ - displays the EQ currently being output by the amp (AM, FM, Tape, CD, DVD video).
• Continuous Tone Test - outputs a low and high note to each speaker (starts at the driver's door and proceeds clockwise around the vehicle).