For audio you might also consider U+2581—U+2588, LOWER ONE EIGHTH BLOCK through FULL BLOCK. And then if you really want to go all out there are sixels, but that’s basically just an image; you probably lose the easy ability to compare them. On the other hand they’re not available in every terminal.
These blocks are great if you need more vertical than horizontal resolution. There are also newer symbols in the Unicode 13 spec that are just the line without the fill.
The same group wants to include a couple others, from different platforms, but the Unicode Script Ad Hoc Group is concerned the new batch may not be as meaningful as the first one.
