[rbanffy]

If we go beyond ASCII, Unicode specifies 2x2 mosaics since ever (they were present in DEC terminals) and 2x3 mosaics (from Teletext and the TRS-80) since version 13. Some more enlightened terminals (such as VTE) implement those symbols without the need of font support.

Or you can use Braille to get 2x4 mosaics, but they usually look terrible.

[jwosty]

I just might have to try this next.

[db48x]

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.

[rbanffy]

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.

[db48x]

Oooh, I didn’t know about those! I’m going to go look them up.

[rbanffy]

There are more details here: https://en.wikipedia.org/wiki/Symbols_for_Legacy_Computing

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.