Part One

Audio System Description

Overview

The audio unit acts as the processor for all audio functions. You can select the audio functions from the front panel, the audio remote (on the steering wheel), or by using the navigation voice control system. The audio display provides the current front and rear audio status. For vehicles with navigation, additional audio information is available by touching the audio button. (See the owner's manual for more details.)

The XM receiver and audio disc changer pass their signals is to the audio unit. In addition, they communicate with the audio unit via the GA-Net bus. Any open connections or short in the wiring in the GA-Net bus circuit will cause audio (including the audio accessories) and navigation functions to appear inoperative.

With the premium sound system, an audio amplifier unit powers the speakers, otherwise the speakers are powered directly by the audio unit.

The audio unit has a built-in EEPROM (electrically erasable programmable read-only memory). This memory holds the audio preset data (AM/FM radio frequency, sound settings) even when the battery power is removed.

Active Noise Cancellation (ANC) system

The audio system is equipped with the ANC circuit in the audio unit.

The ANC system works to cancel engine booming sound up to about 2,000 rpm. The audio unit receives the engine speed pulse (NEP) from the ECM/PCM and outputs a sine-wave-sound through the audio speakers to cancel low-frequency noise from the engine. The ANC system also uses two microphones to detect and monitor low frequency noise in the passenger compartment. The microphones feed information back to the audio unit which adjusts the speaker output to reduce the noise. The ANC also receives input from the door open/close (INTR LT) signal from the MICU. Anytime a door is opened, the ANC system temporarily stops working.

Speed-sensitive Volume Compensation (SVC)

The audio system is equipped with speed-sensitive volume compensation (SVC). The audio unit receives the vehicle speed pulse (VSP) from the ECM/PCM. The system processes the speed input and increases the audio system volume level as the vehicle speed increases to compensate for the various interior noises that occur at higher speeds. When the vehicle slows down, the volume returns to its normal level. The SVC has four settings: SVC OFF, LOW, MID and HIGH that can be adjusted using the audio unit. The SVC comes from the factory with MID set as the default (see the owner's manual for more information).

Telematics Muting Logic

The navigation system allows voice control for the audio, the XM, and the CD player. The navigation system uses the GA-Net bus to communicate the voice control commands to the audio unit. When using the navigation TALK/BACK button, the audio is muted on all speakers and you hear navigation sound on the front channels. When using the navigation or route guidance (RG), the front speakers provides the navigation sound and the rear speakers continue to play the audio. For more information, see the navigation and HFL sections. The outline of the muting logic is shown in this table.