Function

Data exchange between the sound amplifier (A2/13) and the possible signal sources such as:

- Radio (A2) or
- COMAND operating, display and control module (A40/3n1) or (in (J))
ICS operating, display and control module (A40/3n1)

Is accomplished via the digital data bus (D2B). The control information as well as the signals from the audio sources (radio, cassette, CD, voice output for navigation) are transferred via the D2B bus.

Signal processing
In order to allow full adjustment of the sound, the sound amplifier (A2/13) has a Digital Signal Processor (DSP), for filtering all signals. In comparison to conventional analog filters, digital filters have significant advantages:

- the filter parameters (sound settings) do not change in the course of time; this means exact reproducibility of all settings.
- lower noise
- the expenditure for components is reduced considerably because the filter parameters can be set with software rather than varying the component values (resistances, capacities or inductivities), which also allows a larger number of possible filter settings.

Sound optimization
Each of the 6 amplifier channels has a separate compensation circuit which corrects the vehicle specific acoustics as required. In addition, additional sound optimization and effects can be called such as speech emphasis or space sound.

Base, trebble, volume, balance, fader and the dynamic loudness function can be adjusted separately.

Noise suppression
The output signals from the 6 output stages are monitored continuously and regulated to keep distortion as low as possible.

Automatic vehicle interior noise compensation (Vehicle Noise Compensation (VNC))
The noise level in the interior of the vehicle is measured with the aid of the sound amplifier microphone (B25/6), connected directly to the sound amplifier (A2/13). The volume of the music output signal is continuously adapted to this noise level. For this purpose, it is necessary for the sound amplifier (A2/13) to recognize which signals in the measured level are vehicle noises and which are audio signals. This is accomplished by comparing the output signal from the sound amplifier with the measured signal. In simple terms, the difference between the two signals is the vehicle noise level.

Diagnosis
The sound amplifier (A2/13) outputs the following messages relevant for diagnosis

- Operating status
- Under voltage
- Internal error in sound amplifier (A2/13)

The messages are transferred to the A40/3n1 or the radio (A2) via the D2B bus and can be read out there via the diagnostic bus (K bus).