Tone and noiseband masking: Level and bandwidth dependence

Earlier findings indicated a decrease of about 4 dB in the ratio of signal level to masker level at a masker level of about 50 dB SL when noisebands were subcritical but not when supercritical [Greenwood, J. Acoust. Soc. Am. 33, 484–502 (1961)]. Schlauch, Weir, and Norton [J. Acoust. Soc. Am. Suppl. 1 71, 573 (1982)] reported a related result. The early data suggested a masking study in which both masker and signal were the minimum width subcritical stimulus, namely pure tones of the same frequency in‐phase, to see if consistent change would occur. Pilot tone‐on‐tone experiments in 1960 [Greenwood, Harvard P. A. L. Status Rpt. 37, 8–9 (1961)] showed a larger drop in ratio since signal and masker were coherent. Further detailed tone‐on‐tone growth of masking curves from over a dozen subjects were obtained in 1967–69 and, with the 1960 results, are reported here. A clear break in slope, of variable abruptness, usually occurs at about 50 dB SL, either rapidly or gradually dropping 5/M ratio by 6 to 8 dB. [c.f. Rabinowitz et al., J. Acoust. Soc. Am. 59, 1506–1509 (1976) for a similar result.] Addition of low‐level wideband and high‐pass noise was found to counteract the change, i.e., to raise the high level section of the growth of masking curve [see also Zwicker, Acustica 6, 365–396 (19561; Viemeister, J. Acoust. Soc. Am. 51, 1265–1269 (1972); Moore and Raab, J. Acoust. Soc. Am. 55, 1049–1054 (1974) for consistent results.] However, use of added narrow bandpass noise at variable frequencies indicates the most effective region in which to add the noise lies, at a frequency ratio of band to masking tone of 1.3 to 1.5, between masking tone and its second harmonic. These results and others [Green, J. Acoust. Soc. Am. 41, 1517–1525 (1967)] appear consistent with the results of increasing bandwidth from subcritical to supercritical widths cited above.