- Open the Audio tab → Voice & mix.
- Make sure Loudness normalisation is on
(it is by default).
- Balance the tracks
with the Voice, Tab sound and Effects sliders.
- Export.
Zoomr measures the whole mix (ITU-R BS.1770) and brings it to −14 LUFS with a −1 dBFS limiter.
−14 LUFS is the level YouTube, Spotify and most platforms normalise to, so your video won't be turned down or sound quieter than others.