Oh, you could probably solve that concentricity error by looking at the subtle repetitive wobbles in the spectrum. Period of the wobble would be related to the

Oh, you could probably solve that concentricity error by looking at the subtle repetitive wobbles in the spectrum. Period of the wobble would be related to the radius from the center, and the amplitude of the spectral shift would be relative to the radius and the concentricity error. I suspect modern direct drive could handle the modulation of their speed. I suspect this has been done already.