I have a gadget that does contain a 12V AC synchronous gear motor (2 Terminals) that i want to hack.

I want to supply the gadget with 12V DC (among other changes).

Up to now i use tiny AVR and a LB1641 motor driver to feed the motor with voltage of alternating polarity. Everything between 20 and 60 Hz with Pulses between 70% and 100% seems to work well.

L1  _____---_____---_____
L2  _---_____---_____---_

But the motor does not run as quiet as from the wall wart supply.

How can i transform the output of the Motor driver into something that is more pleaseant to the motor and my ears?