Busy or Ringing? Parameters Used in Tone Interpretation by Telephone Users
Michael Schoeffler, James Sheridan · The Journal of the Acoustical Society of America · 1966
Foreign telephone systems have somewhat different tone signals from those used in the USA to inform a caller as to whether the distant telephone is ringing or busy. In order to prepare for the eventual extension of American direct dialing to overseas points, we measured the effect on user interpretation of frequency, modulation rate, repetition period, and ON/OFF ratio of the telephone tones. Test subjects identified a large set of tones as being ringing, trunks busy, lines busy, or none of these. The set included most of those tones which are currently in use in various countries. The data were used to provide a 2-dimensional mapping of the signals. The results indicate that low repetition rates are interpreted to mean “ringing” and high repetition rates mean “busy,” regardless of any modulation of the fundamental frequency of the tone. However, for intermediate repetition rates, a modulation that makes the tone sound rough increases the tendency to interpret such signals as “ringing.” Fundamental frequency of the tones and ON/OFF ratio were found to be relatively less important variables.