Background Music Demo

This is a really brilliant demo, Jackson. Thank heaps.

But I have a project that will have the sound of Guitar, paino and vocal on the same slide. I want them to play together. But how can I use Jackson's script to adjust the volume of each audio?

var audio = document.getElementById('bgSong');
audio.volume = 0.0;

I've never coded, so I don't really know how to make this work

Any help would be much appreciated?

Thanks,

Virak