a light beam is scanned on a track of a recording medium , the track having a first track region and a second track region , each track region having a physical property that has recurring deviations . a wobble signal is derived from the light beam , the wobble signal having information associated with the recurring deviations . whether the light beam is at the first track region or the second track region is determined based on a frequency , a period , or a pulse width of the wobble signal .