'I have a circuit in which a fixed voltage is passed via a potentiometer connected between +9v and 0v, is then buffered and determines the start frequency of a voltage controlled filter.'

by a potentiometer - you mean a volume pedal or some such...?

there is then some sort of compresser or noise gate, and you want more headroom - to stop the signal disappearing or distorting.

Is that roughly what we are talking about?