# What is ducking (or sidechain)?

Ducking is automatically lowering the music whenever someone speaks, and letting it come back up when they stop. It is what makes a music bed sit under a voice instead of fighting it — and doing it by hand means drawing a volume curve around every sentence.

![The music level drops while the voice is speaking and rises back in the gap between sentences. The curve follows the voice clips, so it stays correct after you cut — you never draw it by hand.](https://mubert.com/tools/cast/docs-media/diagrams/what-is-ducking.svg)

You have heard it in every radio ad and podcast intro. When it is done well you do not notice it; when it is missing, the voice sounds buried.

Cast ducks automatically, following your actual voice clips, so it stays correct even after you cut the speech.

## Related

- [Why does the music get quieter when someone talks?](https://mubert.com/tools/cast/docs/auto-ducking)
- [The music is too loud under my voice — what do I fix?](https://mubert.com/tools/cast/docs/music-too-loud)

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Source: https://mubert.com/tools/cast/docs/what-is-ducking · Cast docs
Last updated: 2026-09-14