Operation wolf (and others) TC0060DCA sound fix.

[terriblefire]

I've recently done some work reproducing the TC0060DCA hybrid for my real operation wolf machine. As a step in this process i profiled an original hybrid chip to get the amplitude response with input value.

The TC0060DCA is a programable attenuator used to do nice fades etc.

Blue line was original, Red was my reproduced board. The curve fits the equation 1.0/(1.0+exp(-10*((x/256.0)-0.6)))

an example patch is supplied which sounds massively better than the current setup. I did not know how to structure the mapping in such a way it could be used by other Taito boards (e.g ChaseHQ/Cont Circus).

example_tc0060dca.patch

Hopefully this is some help

[terriblefire]

Created a pull request for this https://github.com/mamedev/mame/pull/13378/commits