Getting sounds back to default?

I have been playing online multiplayer (Thanks S397 for free online) and been messing with the sounds to be able to hear people over he car sounds and now back in single player the sounds are really hard to hear and with my tinkering haven't been able to get it back to how it was from default .
Can Anyone help with how to return the sounds back to how it was when i first fired up this awesome Sim?

 

I use the Windows sound mixer to reduce the game sound compared to our TeamSpeak (to do when the game is running).

 

Im going to do the same just hope to return game sounds to default then start again .