I built a small test circuit (500ohm resistor and 220uF cap in series) which should mimic that “clean sync” cable connected to DIN c-sync pin. I scoped the output of the that circuit vs a standard cable with composite video as sync – pictures here. While the c-sync output is cleaner (no chroma burst or video content), leading sync edges are less sharp and sync tips are narrower which are both bad for digitization. OSSC still synced fine with the MD1 I had for testing, so there may be some differences between models. I’d also like to know the resistor value used in that cable which can lead to different results. Anyway, I’d recommend normal composite as sync cable over a passive c-sync cable like that.