Ducking is the thing a radio station does when the presenter talks over the intro: the music drops, the voice sits on top of it, and the music comes back. Done well, nobody notices it happened. Done badly, it sounds like somebody knocked the volume knob.
Getting it right is not difficult, but it is not one setting either.
How far down. Expressed as a percentage of normal volume. Too little and the announcement fights the music; too much and the sudden silence is more startling than the announcement. Somewhere around a quarter to a third of normal is a sensible starting point for speech over music, and a shop with quiet ambient music needs less reduction than a workshop with something energetic playing.
How fast it fades. This is the number people leave at zero and then wonder why it sounds harsh. An instant drop is audible as a click or a lurch; a fade of roughly a quarter to half a second reads as intentional. The fade back up can be slower than the fade down — that asymmetry is what makes it sound produced.
How long it holds. The music must not start climbing while the last word is still being spoken. A short hold after the announcement finishes, before the fade back begins, removes the effect entirely.
Ducking is a property of the background music rather than of each announcement, so it is configured once and everything that plays over the top inherits it — scheduled announcements, typed speech, push-to-talk from a phone, and the bell. There are four steps, and the last one is the one people skip:
After that, everything that plays over the top ducks automatically: scheduled announcements, typed speech, push-to-talk from a phone, and a bell.
Deliberately different. An emergency alert does not duck the music — it stops it, and it suppresses everything else scheduled until somebody resets it. Ducking is a politeness feature; an emergency is not a polite event, and a system that let a scheduled lunch bell play halfway through a lockdown message would be worse than no system.
Bad ducking is nearly always one of four things, and three of them are settings rather than equipment: no fade at all, which is by far the most common cause; too much reduction, so the near-silence draws attention to the mechanism; no hold time, so the music returns over the final syllable; or an announcement that is too quiet, which tempts you to duck harder instead of fixing the level:
Does ducking work with an external source, like a radio or a phone plugged into the amplifier?
Not directly. Multilarm controls what it plays itself. Music from a separate device on another input is outside its reach, so if you want ducking, let Multilarm own the music — internet radio streams and local files both count as music it owns.
Does it duck for push-to-talk as well as for scheduled announcements?
Yes. Anything routed as an announcement ducks the music, including live speech from a phone browser.
Can different zones duck differently?
Each output has its own audio settings, so a shop floor and an office can be tuned separately.
What happens if the announcement fails halfway through?
The music restores. The fade back is driven by the announcement ending, and an announcement that stops early still counts as ending — the music does not stay stuck at a low level.
Is there a delay between the duck and the announcement starting?
There is, and there should be. The fade down begins fractionally before the speech so the first word is not swallowed by music that is still on its way down.