Ideas for a new circuit

[jorgen.bergfors at idg.se]

Hi synthesists.

In an idea for a new synth module, I need a circuit that peaks at a certain 
input voltage and then reduces it's output for higher and lower voltages.
The output shold be a voltage, say 5 volts, at 2 volts and then gradually 
decrease in amplitude to 0 volts when the input reaches 1 and 3 volts. Above 
and below that, it should have no output. 
It should be fast enough to follow audio input signals.
Any circuit ideas?

/Jorgen