It's an angry sounding thing: not sonorous like an old Ferrari V12, but something purpose built to destroy its competition. The quick rise in revs as the turbos suddenly spool up make it all the more dramatic.
The C11 was the successor to the 1989 Le Mans-winning Sauber C9, which used an evolution of the M119 twin-turbo V8 found in the C9. The M119 started life as a V8 in Mercedes' road cars, but underwent significant tuning to become the 700+ horsepower monsters you see here.
So, if anyone ever tells you turbocharged engines don't sound good, point them in this direction.