How to write an indicator?

I had difficulty writing a subject, since I had not done this before, but I wrote it in the sense, but at a very primitive level. For channels 8-10, that is, peak ones, I know how to write, but I wanted something more global, for example:
So that the evyk on the screen looks more or less like a sinusoid, so that
it reacts to changes in tone, etc., but not only in volume.
Maybe someone has done this? The best idea will be implemented in Player, which I'm currently finishing. Moreover, 1/3 of the screen is allocated for the indicator.

Frequency, peak in 3 columns (lines) are not accepted for consideration.
Can someone post here a document on the music coprocessor?

PS: Player will most likely be universal, that is, everyone can write your own shell (design it in your own way) for it. Whoever is interested in this can
throw entry points into the main Player code block.

With respect, SP/PoS.