[Stk] fast time domain filter implementation

[Emile Vrijdags]

I'm implementing an application that uses a lot of resources. And after 
profiling I see that about 90% of the application's execution time goes 
into the
StkFloat Filter::tick(StkFloat)
function.
I also see that the filter class and tick function are implemented with 
std::vectors, and my profiler says 59% of the time of the tick function 
is spent on operator[].
So I guess this can be done faster, but I have no idea how to do that. I 
have tried using iterators, but they were even a little slower.

Maybe someone knows of a free optimized filter implementation (time 
domain), or knows an obvious way to improve performance of that code 
segment?

(I'm using intel c++ compiler and intel vtune profiler on win xp SP2 32 
(intel core duo cpu))

Emile