Sound amplifier, function - GF82.62-P-3100-04RM

The data exchange between the sound amplifier (A2/13) and the COMAND operating, display and control unit (A40/3) takes place via the Media Oriented System Transport (MOST). All the control information and audio signals (radio, cassette, CD, navigation voice output) are transmitted via the MOST.

Signal processing 

In order to make possible the diverse adjustments to the sound, the sound amplifier (A2/13) has a digital signal processor which carries out the complete signal filtering. In comparison to analog filters digital filters exhibit several distinct advantages:

• The filter parameters (tone settings) do not change in the course of time which means that it is possible to reproduce all the settings exactly.
• Less noise,
• The cost of components is reduced considerably as the filter parameters are adjusted by the software and not by varying component values (resistances, capacitances or inductivities). The number of possible filter settings also increases as a result.

Noise suppression 

The output level of the six 6 high-level stages is constantly monitored and regulated such that distortion is kept to a minimum.

Sound processing with high resolution 

All 6 amplifier channels are provided with a frequency response characteristic which is individually designed for the vehicle acoustics. In order to achieve this, digital filters of a higher order are used.

Sound optimization 

Further sound optimizations and effects such as voice-emphasized, driver-optimized, or room sound can be called up. Bass, treble, volume, balance, fader and the dynamic loudness function can be individually set.

Fader with "Baby Sleep" function 

The Bose fader should maintain the full sound quality, even if the sound playback is controlled more to the front or to the back. As the bass is produced at the back on the rear shelf, without the Bose fader the bass would be faded out, the more is faded (regulated) to the front. This preserves the full bass playback.

"Baby Sleep" function 

When the system is regulated to the front, the bass playback remains fully operative during the first 9 regulation steps.Not until position 10 is the bass completely faded out whereupon sound components are no longer heard from the rear area (including bass), i.e. from the loudspeakers behind the B-pillar.

Suppression of the interfering noise 

A dynamically controlled limiter function monitors the output signal and adapts the level so that a maximum of usable sound pressure is achieved while distortions are largely suppressed.

Dynamic Range Optimizer (DRO) 

The noise level inside the vehicle is measured using the sound amplifier microphone (B25/6) which is connected directly to the sound amplifier (A2/13). The music output is constantly adapted so that the influence of superimposed driving noise is compensated. To do this, the sound amplifier (A2/13) must detect which signals of the measured level are driving noise and which are audio signals. This is done by comparing the sound amplifier (A2/13) output signal with the measured signal.

Diagnosis 

The sound amplifier (A2/13) makes available the following messages relevant to diagnosis:

• Operating status
• Undervoltage
• Internal fault in the sound amplifier (A2/13)

The messages are transmitted via the MOST to the audio gateway control unit (N93/1) and can be read out via the data link connector (X11/4).

In order to test the MOST system when installing and to pinpoint any fault sources or in order to be able to reproduce faults which have occurred during operation, a diagnosis mode has been implemented in the sound amplifier (A2/13).