Miller and Heise [J. Acoust. Soc. Am. 22, 637–638 (1950)] defined and measured the trill threshold. They found that a frequency difference of about 15% was needed for two alternating tones to be perceived as such. We made similar measurements between 250 and 4000 Hz and obtained quite different results at all but the 250‐Hz frequency. Our results show a frequency dependence similar to that of critical bands, with the trill threshold about one‐quarter the size of the appropriate critical bands. In addition we measured the trill threshold in the case of the 1000‐Hz signal at modulation rates of 2 and 8 Hz, as well as the 5‐Hz rate used by Miller and Heise. There is a significant drop in the trill threshold at the 2‐Hz modulation rate.
Subject Classification: [43]65.75, [43]65.54; [43]75.10.
