An apparatus for demodulating a data signal read from a recording medium, in which data is recorded on at least a portion of the recording medium. The data is recorded using a recording system having a substantially constant linear velocity. In this manner, the recording medium is rotated at a substantially constant speed during the reading of data signals such that one of a frequency and an amplitude of the read data signal varies. The apparatus includes a signal processor for processing the read data signal in response to a change in one of the frequency and amplitude to produce a processed data signal suitable for demodulation. Once the processed data signal is produced, a demodulator operates to demodulate the data signal and to produce a demodulated data signal.