Tracking control in apparatus for fast reproducing digital information signal from magnetic tape

In a helical scan digital magnetic reproducing apparatus having a rotary cylinder, magnetic heads mounted on said rotary cylinder, and a magnetic tape wrapped around said rotary cylinder and which has a digital information signal recorded on a plurality of recorded tracks so that said magnetic heads scan said recorded tracks to read said digital information signal, a tracking control for controlling the speed of said magnetic tape in order for said magnetic heads to precisely trace said tracks, wherein said reproducing apparatus has a standard playback mode in which said apparatus makes playback operation at a normal speed and a fast playback mode in which said apparatus makes playback operation at a higher speed than said normal speed, each of said plurality of tracks is divided into a plurality of blocks each of which has recorded thereon said digital information signal, and an identification signal including a track number for indicating the corresponding one of said tracks and a block number for indicating the corresponding one of said blocks, and at least one particular block of said blocks of each track has recorded thereon said digital information signal for said fast playback mode, said particular blocks of said tracks being arranged on said plurality of tracks in such a manner that in said fast playback mode said magnetic heads scan said particular blocks along their scan path on said magnetic tape, said tracking control comprising:

• fast reproduce control means for controlling said magnetic tape to be transported at said higher speed than said standard speed;
• means for detecting positional error between the track of a reproduced one of said blocks and the track of said particular block on the basis of said identification signal of said reproduced block which said heads have reproduced and generating a track error signal corresponding to said positional error;
• tracking error detection means for detecting positional error between said magnetic heads and a target track on the basis of the signal reproduced by said magnetic heads and generating a tracking error signal corresponding to said positional error;
• switching means for selectively producing one of said track error signal and said tracking error signal;
• phase control means for controlling the speed of said magnetic tape on the basis of the output from said switching means so that said positional error can be reduced to zero;
• and
• control means for controlling said fast reproduce control means and said switching means to operate, wherein said control means, in said fast playback mode, controls said fast reproduce control means to operate, thereby accelerating said magnetic tape to said higher speed, and when said magnetic tape has reached said higher speed, controls said switching means to produce said track error signal, and also when said track error signal has entered in a certain range, controls said switching means to produce said tracking error signal.