Audio Signal Switching Transistor For Shutter Release
The capacitor and diode are important elements of the circuit.  They allow a steady base current when audio is present, even though the audio swings both positive and negative.  Without the diode and capacitor, the transistor will be off for part of every audio cycle.  This is not likely to be what the camera wants to see.

By the way, you want to close the transistor when audio is present, not open it.  A closed switch conducts (is on), a open switch is a open circuit (is off).