Cadence is about things happening with a steady, predictable rhythm so that events, such as PI Planning and system demos, can be planned into the schedule in advance. This means that there is not much overhead or time spent looking in diaries or rescheduling these events.
Synchronisation means that the events across a whole agile release train (ART) or even solution train occur at the same time so that planning can be done across the whole ART and regular integrations and reviews can take place with the teams at the same point in the programme increment (PI). It also help the ART assess how well it is progressing towards the PI objectives that were agreed at PI planning
