Speed-dependent volume adjustment
The speed-dependent volume adjustment (abbreviation GALA , also GAL , English also Speed Dependent Volume Control (SDVC), Speed-sensitive Volume Control (SVC), or Speed Compensated Volume (SCV)) is a convenience function for audio playback in motor vehicles . The volume is adjusted depending on the driving speed. Such an adjustment can be made for the car radio , CD player and the navigation system. The aim is for the vehicle occupants to always perceive the same volume as the driving noise.
GALA signal
The basis for this is the GALA signal (also GAL signal), which is generated by the vehicle's speedometer .
In newer vehicles, the GALA signal is located on the ISO plug for the power supply (pin 1), in older vehicles this supply line must be integrated later. In vehicles from the mid-eighties, an electronic speedometer is often already used, here the square- wave signal required for the GALA function can be tapped relatively easily on the speedometer feed.
Current vehicles can have a complete computer-controlled instrumentation and use, for example, the CAN bus to transmit the information. Such highly integrated vehicles often already contain a proprietary navigation system; for retrofitting a navigation system with GALA signal and ISO connector, an additional electronic component (e.g. a CAN bus adapter) must be used.
In older vehicles with mechanical transmission (shaft) of the speed information to the speedometer, a transmitter must be integrated into the speedometer cable, which converts the rotation of the speedometer cable into an electrical signal via a magnetic contact or Hall switch .
Use for makeshift position determination
Some navigation systems use the GALA signal not only to regulate the volume but also for redundant or alternative position determination, which is used when the GPS signal is interrupted, for example in long tunnels . In addition to the GALA speed signal, current navigation systems also use inertial navigation to determine changes in the direction of travel more precisely. The function of the navigation is in principle secured by the GPS antenna, the GALA connection is optional, but it helps to a much more precise navigation especially in city centers and in situations with poor GPS coverage (e.g. also when driving through long tunnels).