Abstract: A rotary magnetic head device in a magnetic recording and reproducing apparatus such as a VTR apparatus and a DAT apparatus which adopts a helical scanning system. In order to prevent the demagnetization of a magnetic tape and reduce a jitter component of a reproducing signal, a head unit moves the magnetic head in the diametrical direction of a rotary drum. The head unit has a bobbin inserted into the center holes of a plurality of spring leaves, and the bobbin is moved in the diametrical direction of the rotary drum by the electromagnetic force produced on the coil wound around the bobbin. A head arm attached to the spring leaf is thereby moved in the same direction, thereby varying the amount of projection of the magnetic head. The amount of projection of the magnetic head is controlled in correspondence with the level of the envelope of a reproducing signal so as to be set at the minimum value in the range in which the output level of the envelope signal is saturated.

Abstract: A standard reference video tape, a source of a standard reference video signal and a source of a variable offset signal are adapted for use with a plurality of time base corrector units. Each unit is capable of playing a video tape to produce a corresponding video output signal containing various viewing parameters such as video gain, chroma gain, set up and hue, the viewing parameters having values which can be varied. The units have slightly different electrical characteristics so that when each of these units is caused to play the same tape at identical parameter values, the video output signals will differ from unit to unit. The referene tape is played in one of the units having parameter values preset for use with this tape, thereby producing a video output signal containing all parameters. The output signal is played together with the reference signal, the reference signal containing the same parameters but with different values. An offset signal is applied to the input of said one unit.