The problem
An hour lasts sixty minutes. Music never lasts exactly sixty minutes. So every hour there is a moment when the planner must decide: let the last song finish and start the new hour late, or cut it and start on time? For a network that takes the news at the top of the hour this is no detail. For a music station without fixed joins, a truncated song is the worst thing there is.
Hard sync: the clock is sacred
In hard sync the hour anchor is fixed at HH:59:59. If music is still playing at HH:59:57 it is faded out in two seconds and the new hour starts exactly at HH:00:00. Truncation here is intended behaviour. The planner therefore fills every slot up to the anchor, even if the last song does not fully fit: thirty seconds of a fading song beats nine minutes of silence or an emergency tape.
Choose hard sync if you take news from an external provider at the top of the hour, if you broadcast in a network where several stations switch at the same moment, or if a show really must start at exactly nine.
Soft sync: the song is sacred
In soft sync the last song plays to its natural end. The hour anchor floats within a window from :58 to :02 and the new hour starts as soon as the song is done. If a song is truncated in this mode, that is a fault. To keep the hour from running far over, the planner looks ahead in the last ten minutes: a music slot that would overshoot the boundary is skipped. Weather, jingles and presentation are never skipped by this rule.
Choose soft sync for a music station where the listener values the song more than the clock, and where nothing from outside must join at the top of the hour.
What it means for the clock
In hard sync the clock may deliberately be overfull; the boundary tidies it up. In soft sync the clock must above all not be thin, because nobody can fill a shortfall, and it may be slightly overfull because the last music slot simply drops. In both modes: the weather is the first element after the hour anchor and starts exactly on it.
At NexRadio the mode is set per station in its settings. Anyone reporting a truncated song as a fault is first asked: which mode is the station in? In hard sync the answer is: that is how it should be.
The hour change in practice
The new hour is ready well in advance so the handover can happen on the second. In the last minutes nothing is changed in the next hour any more. The playlist shows the next hour from :55 alongside the current one, so a presenter sees what is coming. An empty next hour at the top of the hour is, by our definition, a critical fault, not an edge case.
Frequently asked questions
Can I switch between hard and soft sync per hour?
The mode is a station setting. In practice a station picks one mode that fits its joins; switching per hour makes behaviour unpredictable for presenters.
Why does the song fade at :59:57 and not :59:59?
Because the fade takes two to three seconds. That way the music is silent at :59:59 and the new hour starts at :00:00 without overlap.
What if the news arrives late in soft sync?
News and other external elements have their own time in the clock. If the file is late, the previous version plays or the slot is skipped, depending on how the slot is set. The weather always falls back to the last successful version.