Signal processing apparatus for disc memory devices

Claim 1

A signal processing apparatus for a disc memory device which includes a disc with a plurality of pits arranged at equal intervals along tracks defined on the surface of the disc, at which pits digital signals are recorded bit by bit and a pickup tracking a predetermined one of the tracks to record signals at the pits or read out recorded signals from the pits, comprising; recording means for processing a source signal to be recorded to change the source signal into the form suited for the recording, and reproducing means for processing a digital signal read out from the disc to generate a reproduced signal, characterized in that there is further provided means for detecting the linear velocity of a track, which is at present followed by the pickup, the linear velocities of the tracks being varied in accordance with the position of the pickup relative to the disc which is rotated at the constant angular velocity, said recording means has an analog-to-digital converter for sampling the source signal at predetermined sampling frequencies and converting a sampled signal into a digital signal, the sampling frequencies being varied in accordance with the linear velocity detected by said detecting means and a low pass filter for filtering the source signal supplied for the analog-to-digital converter, the cut-off frequency of which is varied in response to the present sampling frequency, and said reproducing means has a digital-to-analog converter for converting a digital signal read out into an analog signal and a low pass filter for filtering the analog signal converted by the digital-to-analog converter, the digital-to-analog conversion and the cut-off frequency of the filter being controlled in accordance with the linear velocity detected by said detecting means.