[andyathome]

Thanks for the feed back.
I have hookd into one of the valves but the sound would only change when that channel was used.
the 4th valve on my excavator opens when no stick movement and dumps back into the tank this results in my sound card changing revs . It slows when sticks moved and speeds up when no movement it is also proportional so you get a steady decrease in sound when sticks moved.
I like the signal reversing idea.
will give it a try and see what happens. Only way to learn is to mess it up and try again.
cheers andy