Observer Reaction to Low-Frequency Interference in Television Pictures

Abstract

This paper presents results of tests to determine how much low-frequency interference can be tolerated in black-and-white television pictures. Various levels of single low-frequency interference were superimposed on a locally transmitted television picture. Observers viewed the picture and rated the disturbing effect of each level of the interference. Ratings were made in terms of preworded comments ranging from "not perceptible" to "unusable." Interfering frequencies from 48 to 90 cycles per second were employed. Just visible interference appears as a flicker. The rate of flicker is the difference between interfering and 60-cycle field frequencies. The most disturbing interference produced a flicker rate of 5 or 6 cycles per second. To be tolerated, the peak-to-peak amplitude of this interference had to be 54 decibels weaker than the peak-to-peak amplitude of the television signal (including synchronizing pulse). For flicker rates of 0.5 and 12 cycles per second, the amount of interference which could be tolerated was larger by 14 and 3 decibels, respectively.