Method and apparatus for obtaining identical output signals from time base corrector unit having variable or different electrical characteristics using a video tape of known parameters

Apparatus adapted for use with a time base corrector unit to obtain a set of offset signal values to be associated with this unit, the unit being capable of playing a video tape to produce a corresponding video signal containing the viewing parameters video gain, chroma gain, set up and hue, the apparatus employing a tape having a known set of parameter values and carrying test patterns, the apparatus comprising:

• [a] a signal comparator having a first input to which a test pattern video output signal can be supplied and a second input to which a standard reference video signal containing the same parameters but at different values can be supplied, the comparator having an output at which both the test pattern video signal and the reference signal appear as a mixed video signal;
• [b] first means coupled to an input of the unit to set it to play said tape using the known set of parameter values, the unit then playing the tape and producing the test pattern video signal, the test pattern video signal being supplied to the first input of the comparator;
• [c] second means to supply the reference video signal to the second input of the comparator;
• [d] a display device having an input coupled to the output of the comparator and responsive to the mixed signal to display same as a composite;
• and
• [e] third means producing an offset signal variable in value, the variable offset signal being applied to the input of the unit, the offset value being adjusted for each parameter in turn to set the parameter value of the test pattern video signal to be identical to the value of the same parameter contained in the reference signal.