Graphs of circles
The equation for a circle is x2 + y2 = r2 To draw one manually, set the drop-down box type of equation to square root of a polynomial, and set parameter b to -1 and parameter d to the square of the radius. You will need to set the ranges of x and y to negative and positive values greater than the radius.
This demonstration draws 8 concentric circles with radii ranging from 24 to 108, and plays a MIDI note whose MIDI pitch number equals the radius. Midi note 24 is 3 octaves below middle C, 60 is middle C and the highest note, at radius 108, is 4 octaves above middle C.