How to create square audio spectrum like this?

I do not see anything more complicated than animating opacity. You could do that with text animators. It is just a matter of picking out some values and figuring out the range you need. I'd start with a symbol text and an opacity text animator.

Maybe this tutorial I just published will help:

That gives you the math. Now all you need to do is figure out the numbers you want to use.

Could be as simple as tying a basic audio expression into a text animator on a line of typed out square symbols. Other techniques could include quantized linear wipes that similarly are tied to an audio channel. Really nothing too fancy going on there.

Mylenium