[sdiy] understanding this one transistor F to V

[Dan Snazelle]

in this circuit, 

http://www.diystompboxes.com/analogalchemy/sch/shocktave.html

the transistor with the diode connected from base to collector (with the cap to grnd and resistor to +v coming off the collector as well, and the ouput of the base going into an oscillator)

is called an F to V

I would love to know how this works, as it is obviously a very low parts count frequency to voltage circuit.

I assume that the rest of the circuit squares up the signal, and those pulses only turn on the transistor above a certain threshold which charges the cap?

but i am not sure

thanks!