The Subjective Effects of Echoes in 525-Line Monochrome and NTSC Color Television and the Resulting Echo Time Weighting

The subjective effect of an echo in a television picture depends not only upon the amplitude of the echo but also upon its time displacement from the main signal. The relationship between amplitude and time displacement, in the form of an echo time weighting curve, has been used as the basis for designing oscilloscope graticules used in waveform testing methods. A series of subjective tests was performed to evaluate the effects of echoes on 525-line monochrome and NTSC color pictures. Observers used a seven-point comment scale, ranging from “not perceptible” to “extremely objectionable” to rate the echo impairments. The test results show that separate positive and negative echo time weighting curves are indicated for monochrome signals and that a third curve, applicable to both positive and negative echoes, is indicated for color signals.