How to show sound level with stagexl audio?

[linuxerwang]

I'd like to create a sound meter to show the sound level, like this: https://ourcodeworld.com/articles/read/413/how-to-create-a-volume-meter-measure-the-sound-level-in-the-browser-with-javascript or https://webaudioapi.com/samples/visualizer/. I am not trying to visualize the input voice, but the level of sound played through AudioElementSound.

Can anybody give a hint how to do it?

Thanks!