Volume adjusting in HyperTTS?


I was looking for a voice that includes American-specific contractions like don’tcha, couldja, whaddaya etc. and found out Matthew by Amazon. But I’m not satisfied with its volume, I think it’s too low unlike other voices. Can I somehow adjust it for both mobile and desktop Anki clients? There’s no such option in the add-on itself when you create audio files.

P.S. The first thing that came to my head is to write a script with FFmpeg or something similar, but I hope there’s another way of doing this.