I can't determine the meaning of "grade"

[teleostomi]

I can't determine the sense of "grade" in this part of "Locusts and Katydids"

A single locust is now heard near noon from a tree two hundred feet off, as I write—a long whirring, continued, quite loud noise graded in distinct whirls, or swinging circles, increasing in strength and rapidity up to a certain point, and then a fluttering, quietly tapering fall.

I first thought this verb "grade" is something like "to make a slope, so that certain movement changes itself gradually from one aspect to another." Is that right?

[Pete]

I can't determine the sense of "grade" in this part of "Locusts and Katydids"

A single locust is now heard near noon from a tree two hundred feet off, as I write—a long whirring, continued, quite loud noise graded in distinct whirls, or swinging circles, increasing in strength and rapidity up to a certain point, and then a fluttering, quietly tapering fall.

I first thought this verb "grade" is something like "to make a slope, so that certain movement changes itself gradually from one aspect to another." Is that right?
I think it means divided into intervals that are sorted according to their quality. I'd say that this is not a common use of the word "graded".