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

Data exchange between the sound amplifier (A2/13) and the other audio components ensues by way of the Media Oriented System Transport (MOST).All the control information and audio signals (radio, cassette, CD, navigation voice output) are transmitted via the fiber optical cable.

Signal processing 

In order to be able to use the diverse tone settings, the sound amplifier (A2/13) is equipped with a digital signal processor, which carries out the complete signal filtering process. In comparison to analog filters digital filters exhibit the following distinct advantages:

• The filter parameters (tone settings) do not alter as time passes. This means exact reproduction capability of all settings.
• low noise level
• The cost of components is reduced considerably, as the filter parameters are adjusted through the software and not by varying the component values (resistances, capacitances or inductances). The number of possible filter settings also increases as a result.

Noise suppression 

The output level of the six 8 high-level stages is constantly monitored and regulated such that distortion is kept to a minimum.

Sound processing with high resolution 

All 8 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.

"Bose Fader" function 

The "Bose Fader" should maintain full sound quality, even if sound playback is shifted more to the front or to the back. As the bass is generated at the back on the rear shelf, without the "Bose Fader" the bass would be faded out, the more "fading" (regulated) is done to the front. This preserves the full bass playback.

"Baby-Sleep" function 

When the system is regulated to the front, bass playback remains fully operative during the first 9 regulation steps. The bass is not completely faded out until position 10 and no more sound comes from the rear area (no bass either), i.e. from the loudspeakers behind the B-pillar.

Suppression of interference noise 

A dynamically regulated limiter function monitors the output signal and adapts the level such that a max. permissible sound pressure is achieved. Any distortion is mainly suppressed here.

Dynamic Range Optimizer (DRO) 

The sound amplifier microphone (B25/6), which is connected to the sound amplifier (A2/13), is used to measure the noise level within the vehicle.

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 sound amplifier 

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 to the COMAND operating, display and control unit (A40/3) or the radio (A2) via the MOST 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).