Apparatus for controlling rotation of a record disk at a constant linear velocity

Apparatus for reproducing from a record medium an information signal of the type including at least one frame of data and at least one transition interval such that maximum and minimum limits are provided for said at least one transition interval and correspond to maximum and minimum transition intervals, and at least one maximum transition interval is provided in each frame of data, said frame of data having a frame period corresponding to the length of time for reproducing said frame of data at a predetermined constant linear velocity, said apparatus comprising:

• transducer means for reproducing said information signal from said record medium during relative movement between said transducer means and said record medium;
• means for producing an output signal at a bit frequency and corresponding to said reproduced information signal, said output signal having portions of opposite polarities so that said output signal includes at least one transition interval;
• clock pulse generating means for generating clock pulses having a constant frequency higher than the bit frequency of said output signal;
• detecting means for detecting the length of at least one transition interval of said output signal by counting the number of said clock pulses generated during each detected transition interval of said output signal;
• determining means for determining, during each of at least one predetermined period selected to be longer than the period ##EQU3## if the number of said clock pulses counted by said detecting means during each detected transition interval in each respective longer predetermined period corresponds to a predetermined number of said clock pulses included in the maximum transition interval which occurs when the record medium is moving at said predetermined constant linear velocity with respect to said transducer means, and for producing a velocity control signal in response thereto;
• and
• velocity control means for controlling movement of said record medium at said predetermined constant linear velocity with respect to said transducer means in response to said velocity control signal.