Monaural beat-tone existence region

Abstract

An experiment was performed which yielded the upper and lower thresholds for beats. A beat-tone existence region, the difference in decibels between the lower and upper beat-tone thresholds, was determined for several frequencies. A primary tone was presented at various sensation levels (−15 to 65 dB SL) and then a beat-tone was added 4 Hz below the primary. Subjects adjusted the beat-tone intensity to obtain the upper and lower beat thresholds. Beats were shown to occur when the intensity of the beat-tone and primary-tone differed by as much as 30 dB. The existence region initially increased as a function of the primary-tone intensity (between −15 and 20 dB SL) and then remained fairly constant (about 45 dB difference) for values of the primary between 20 and 65 dB. The data suggest that experiments which depend on the monaural perception of beats to indicate when a combination tone has been cancelled (i.e., the probe-tone, cancellation-tone method of measuring the intensity of CT) may error in their estimation of the CT intensity if the CT is actually above about 35 dB or below threshold (but still physically present). When the CT is assumed to be between 15 and 35 dB SL the probe-cancellation-tone method of estimating the intensity of a CT was judged as adequate.