The goal of the ALA is to support the VNC operation by slightly boosting weak signals. This also helps in
compensating the level difference of the input signal from CD and radio. Normally, the radio signal is much
weaker than the CD input level, so when users switch between them, there is an audible difference. For this
reason, the ALA in needed.
The range of this adjustment is dictated by the current MNR, speed, volume and users’
VNC amount (user element). In the worst-case scenario, where the MNR is minimal and the VNC amount is
maximal, the ALA should have maximum sensitivity to the input level. When the environment conditions start to
get better, meaning that the MNR is increasing, the ALA should become less sensitive to the input level. Users‘
VNC amount should also directly affect the ALA sensitivity.
The ALA is meant to be applied to the Entertainment channels only. However, it should only react if there is a
change in the defined parameters, evaluated at the loudest source and at MID range.
The core of the ALA implementation is the Compander. Some parameters can be overwritten according to the
VNC level amount that users set, MNR, speed, and volume. For the remainder of this document, they will be
referred to as DTP. The DTP are sent to the DSP from the Tuning Tool through
the Global Parameters.
The ALA consists of the following submodules:
- the Compander
- Input Filters (BPF, HPH and BPH)
- the respective Mixer
- Delay Line
- AlaGain
The expander region of the ALA Compander should be deactivated by setting its threshold equal to that of the
Noisegate. This way, there are only three active operating regions: Noisegate, Linear and Compressor.