How to mix two audio files into one WAV

Lay out both files

Open Montaje (session) and connect each audio file to its own track. If you want a voiceover to come in over a beat, leave the music at second 0 and move the voice to its entry point. To join two songs, move the second one to the end of the first or overlap them during the transition.

Select a clip to check its position and length in the property fields. If the second source appears too far away, use Encajar (fit) and adjust Posición en sesión (position in session) instead of dragging at a low zoom level.

Decide which one should stand out

Play from a few seconds before the entry. Lower the Volumen de pista (track volume) of the beat if the voice gets lost, or adjust the Ganancia del clip (clip gain) if you only want to change one section. Toggle Solo to tell which source dominates. Clear any solo and mute states you no longer need and listen to the sum. When joining songs, you can create a crossfade to share the transition between them.

Check the mix

Open Opciones → Exportar mezcla… (options → export mix) and use Comprobar niveles (check levels). If the sum gets much louder in the overlap, first lower the source that masks the other. Peak protection can lower the output level if it gets close to clipping. Export the WAV and listen to the entry point again in a player on your device.