The attenuator has been realized employing the "soft step" technique that reduces the audible DC click at
the speaker outputs by dividing the 1 dB step into several smaller-amplitude, longer duration transitions.
5.5.4 VOLUME CONTROL
The volume stage controls the level over a +15 dB..-79 dB + mute range in 1 dB steps. The volume atten-
uator is also realized with the soft step circuitry.
5.5.5 TREBLE FILTER
The treble filter consists of a second order resonating filter with programmable center frequency. The
boost/cut range is !15 dB in 1 dB steps.
5.5.6 BASS FILTER
The bass filter consists of a second order resonating filter with programmable center frequency and quality
factor. It is also possible to set and defeat the DC mode both in cut and in boost. The boost/cut range is
!15 dB in 1 dB steps and the attenuator features the soft step circuitry.
5.5.7 SPEAKER ATTENUATORS
The speaker attenuator driver circuit allows separate volume control for each of the four outputs. The level
is controlled over a +15 dB.. -79 dB + mute range in 1 dB steps with soft step.
An output buffer provides DC shift to a typical 4V level and an AC gain of +4 dB.
The source of each speaker output circuit can be chose among the following configurations:
– tone control output via external AC coupling (coupling shared by front and rear channels);
– tone control output via internal DC coupling (coupling shared by front and rear channels);
– rear seat audio (only for rear channels).
It is furthermore possible to mix an external source (typically the chime source) on all the four outputs,
selecting on which outputs the mixing must take place (any combination is allowed). The volume of the
mixing source cannot be changed internally.