Auto volume control

[RodH]

Hi, does anyone have sample circuits for what GM calls "GAL".
ie: automatic volume control in a vehicle, to compensate for road noise as the speed increases.

I had some ideas about hooking an F-V converter to a VGA but before I go reinventing this, I though I'd ask you guys.

I gather the top-end versions include tone adjustment as well as volume adjustment since some frequencies need more of a boost than others. Anyone got any details/URLs?
Thanks,
Rod

 

[a31ford]

Rod,

In the world of "Commercial Sound" we use a thing called an "ANCA" Ambient Noise Controlled Amp. the basic workings of it are:

Internal sense of "program"(what is going to the speakers), from there, an external "mic" phased 180deg. out of phase with the "program source input". both are combined in an op-amp style system, with a "pre-gain" and "log level" ambient vs. program setting. eg: for every 3db of "noise" unit can be programmed to move up to 9db/step. to a limit of "X" .

The Mic. and internal sense, work in "null" format, anything in the area "seen by the Mic(s)", that didn't come from the program input source, is construed as "noise".

These systems are very common in shopping malls, food courts, as well as gathering halls and sports stadiums.

P.S. mic. placement is VERY critical.


Regards,
Greg,

Called "Mr. Fusion" by the Locals