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Fig. 13. Relation between echo amplitude and echo delay for double-excursion K = 0.3 in characteristic.
linear term has been effected. The simple rule is that G ' will be used on the shorter echo delay side of the intersection, and G will be used on the longer echo delay side.
To recapitulate the discussion, it appears that the description of a very short-delayed echo in terms of response and phase characteristics up to the cutoff frequency is a function of some combination of echo amplitude and echo delay. Approximately, at least, the description is independent of either parameter alone, provided that the other varies in a suitable inverse manner in the combination.
If the description is thus independent, it means that the distortion caused in any given signal is similarly independent, and further, that the picture impairment
caused in any given picture by this signal distortion is similarly independent.
Thus the relationship in the combination between echo amplitude and echo delay describes the required variation of the former as a function of the latter to result in a constant picture impairment. This was, of course, exactly the aim of Fig. 7, and it is now possible to consider the expectation, from the largely geometrical considerations which have been developed, of the course of the curves in that figure toward the very short echo delays.
The relationship described is obviously that of the equations (2). Since R and $ are taken as constants, the course of a is the reciprocal of the compromise course of the functions F and G, respectively. At this point it is desirable.
586
May 1953 Journal of the SMPTE Vol. 60