Audibility region of combination tones

This paper describes research on combination tones of the type f1 − k (f2 − f1. Such tones are audible during stimulation by the two frequency components f1 and f2, with f1 < f2. The results of the experiments suggest that these combination tones are audible only in a restricted frequency region below f1. The lower limit of this “audibility region,” for the combination tone 2f1 − f2 (k = 1), was determined primarily by the level of the lower stimulus component L1 and additionally by L2. The width of the audibility region appeared to be highly subject dependent. The lowest stimulus level for which 2f1 − f2 was audible was 15–20 dB SL if both stimulus components had equal levels. If the lower component was set at 40 dB, then the higher one could be reduced to 4 dB before 2f1 − f2 reached threshold. Higher‐order combination tones could be perceived up to k = 5 or 6. At 40 dB SL, the lower limit of the audibility region was approximately the same regardless of the order (i.e., independent of k). The width of the audibility region could not be explained completely by the amount of interaction of the mechanical stimulation patterns corresponding to f1 and f2. In addition, it is demonstrated that these combination tones may play a misleading part in masking experiments. The detection threshold of a simple tone masked by another simple tone may be determined by the detection of a combination tone of the type f1 − k (f2 − f1), even at a low level of the masker.