Subjective quality of television pictures impaired by short-delay echo

Quality-grading tests have been made on the effect of an undistorted echo of positive or negative polarity and with delay in the range 200¿1300 ns, in a 625-line monochrome television system. The results apply also to the effect on the luminance component of a colour signal. It was found simplest to express echo magnitude in terms of the magnitude of signal plus echo. A logistic relationship between mean picture-quality grading and logarithmic echo magnitude then applies, and the shape of the curve is independent of delay. A mathematical model is described to represent the complete relationships between picture quality, and echo delay and magnitude. Summarised results are given in terms of mark points of subjective impairment. The (signal + echo)/echo ratio at the 1-imp mark point, or midopinion condition, varies from 9 dB at 200 ns to 20 dB at 1300 ns for positive echo and 1 dB to 16 dB for negative echo. At the ¿-imp mark point, the variation is from 14 dB to 25 dB for positive echo and 7 dB to 22 dB for negative echo.