Headphone interface functions

In the case of 'Rear Entertainment' equipment, the users in the rear have the same control functions available as the users in the front. However, the front and rear functions can be used independently of one another. This possibility enables simultaneous output of two different audio sources in the vehicle.

Brief description of components

Headphone interface (KHI)

The headphone interface (KHI) is a separate control module in the MOST framework and it is the interface between the MOST bus and the headphones. Audio and control data are supplied via the MOST bus as input signals. The audio data is supplied by the control modules (tuner, CD changer, DVD changer, etc.) to the headphone interface. Two sets of headphones can be connected to separate outputs for sound output at the headphone interface. The headphone interface (KHI) is fitted under the rear seat on the right at the video module 5 Drive.

Rear center console switch center (BZMF)

The rear center console switch center (BZMF) has the same functions as the front center console switch center (BZM). The rear center console switch center (BZMF) contains the Rear Controller, the rear center armrest switch blocks and the headphone connection module.

Rear Controller (FCON)

The folding Rear Controller (FCON) is the operating unit to control the Rear Entertainment functions at the Rear Display (FD) on the backrest of the driver's seat and Rear Display 2 (FD2) on the backrest of the passenger's seat. Operation and structure of the Rear Controller (FCON) are identical to those of the Controller in the front (CON). However, the functions for front and rear are different. The Rear Controller (FCON) is fitted in the rear center console switch center (BZMF).

Headphone connection module (KHA)

The headphone connection module is the interface between the 'Rear Entertainment' equipment and the headphone users. The KHA picks up the audio signals for the headphones via two switched headphone connections. There are also two rotary controls for setting the volume on the headphones and a search run button to change the CD tracks or radio stations. The headphone connection module (KHA) is fitted at the end face of the rear center armrest.

K-CAN SYSTEM data bus

The K-CAN SYSTEM data bus is the data connection between the instrument cluster and the control modules in the chassis and suspension, drive and body sections. Information is exchanged with data telegrams.

MOST bus

The MOST (Media Oriented Systems Transport) bus links the audio, video and navigation system Information relating to function requests is transmitted to the relevant control modules by means of MOST bus messages.

Main functions

Function of the headphone interface (KHI)

The headphone interface can process two different audio sources with different settings. The audio data is supplied by the control modules (tuner, CD changer, DVD changer, etc.) to the headphone interface via the MOST bus. The headphone interface processes the arriving data for each set of headphones separately. The processed audio signals with the set volumes lie at the two headphone outputs. If the headphone connectors are plugged in, the signals are passed on to the left-hand and right-hand side of the headphones.

Settable functions:The following functions implemented in the headphone interface can be set by the user:

• Volume
  
• Balance
  
• Treble/Bass
  

Non-settable functions: These functions implemented in the headphone interface are set automatically and cannot be influenced by the user:

• Loudness: Raising the bass frequencies with small listening volume for compensation of the level-dependent listening sensitivity
  
• IVA (Individual Virtual Acoustic): natural interior sound
  

Output of audio data

The headphone connection module has two switched headphone connections. If headphones are plugged in, sound is output across the headphones connections. Plugging in the headphones changes the level of the AF signal in the rear center console switch center (BZMF). It is always the same source that is heard in the headphones.

The user in the rear has the possibility to choose another source. This makes it possible to output two different audio sources at the front and rear. The vehicle loudspeakers are intended for sound output of the source selected at the front. The headphones are for the source selected in the rear.

Multi-user rules

The functions in the vehicle are provided by various control modules. The users in the rear access the same control modules as the users in the front. In order to prevent conflicts when accessing one function, rules have been laid down for the following functions.

• Headphones not connected:If no headphones are plugged in, the sound output is via the vehicle loudspeakers. In this case, access is only possible to one source, e.g. the radio. If the users in the front and rear access the same source, the last set value of the other user is overwritten, e.g. change of the radio station, volume, etc.
  If one user wishes to change the source, e.g. from radio to CD, a switch is made to the last selected source and the sound is output across the vehicle loudspeakers. If a switch is made from one source to another, the status indications in the displays are updated.
  
• Headphones connected: If at least one set of headphones is plugged in, the use of two different audio sources is possible. The sound of the audio source selected in the front Central Information Display (CID), e.g. radio, is output across the vehicle loudspeakers. The audio source selected in the Rear Display (FD) and Rear Display 2 (FD 2) is output on the headphones, e.g. CD.
  
• Exceptions: It is not possible to watch a DVD video on the Rear Display (FD) and Rear Display 2 (FD 2) and to listen to audio across the headphones, as the DVD changer can only output one medium. For this reason, it is not possible to listen to an audio CD in the DVD changer across the vehicle loudspeakers either.
  
• Rear lockIn order to prevent adjustment of the source by users in the rear, a rear lock can be activated in the Central Information Display (CID). The rear lock is enabled and disabled in the main menu ”Settings” via the ”Code” menu item. The users in the front still have the possibility to change the source. It is not possible for the users in the rear to overwrite the source. This ensures that children can only get to see a certain DVD.
  

Settings

• Settings with Rear Controller (FCON) at the Central Information Display (CID):The following functions can be set in the ”Sound” audio menu item. The ”Sound” menu item is integrated in the ”Memory” menu item. The headphones must be plugged in to enable setting of the functions.
  - Balance:The balance is set by changing the volume in the left-hand or right-hand channel of the headphones. If a maximum value is set, e.g. left, the right-hand side is muted.
  - Treble/Bass:For the treble and bass setting, the sound can be changed in the range from +/- 10 dB in 1 dB steps.
  
• Settings on the headphone connection module:The following functions can be set at the headphone connection module:
  - Volume: The function of the volume adjustment is the same for both sets of headphones. However, the volume setting is performed separately. To set the volume on the left-hand and right-hand headphones, turn the relevant rotary knob to the left or right.
  - Changing CD tracks or radio stations:The CD track or radio station can be changed in the relevant function by operating the search run button.
  

Notes for Service department

If the status ”Headphones connected” or ”Headphones not connected” is displayed during the diagnosis request, check the AF signal level at the input of the rear center console switch center (BZMF).

The headphone interface (KHI) can be flashed via the diagnosis interface. The headphone interface (KHI) also contains a fault memory for diagnostic purposes.

The headphones are not supplied as standard. Any commercially available headphones with an impedance of 8 - 600 Ohm can be connected at the headphone interface. The jack diameter is 3.5 mm. The output power of the headphone interface (KHI) is 200 mW at 32 Ohm.