Free music software: This video demos Sync Unit DC – a free solution for syncing hardware instruments in software based music setups. It uses audio ports instead of MIDI to provide the best possible synchronization.

By default, it provides a normal 24 pulses-per-quarter-note DIN-sync signal for Roland instruments, but 12, 48 and 96 ppqn are also available for other applications. The signal can also be shuffled in many different ways, keeping you in control over the groove and feel of your patterns.

via rv0soft:

The left plugin window is the sync going to a Roland TR-606, the right window is the sync going to the Roland TB-303. An audio interface with DC coupled outputs was used (Motu Ultralite).