Muralidhar R. Kudumala
Electr. Eng., Univ. of Oklahoma, Oklahoma City, OK 73170
Blas Espinoza-Varas
Univ. Oklahoma Health Sciences Ctr., Oklahoma City, OK 73170
An important issue in audio coding is the detection of quantization noise masked by speech. This investigation examined how different frequency regions contribute to the detection of broadband noise masked by a vowel. The vowel was synthesized by addition of the first 32 harmonics of a 200-Hz fundamental, with amplitudes appropriate to /i/. Broadband noise was synthesized by random-phase addition of the harmonics of a 10-Hz fundamental that fall within the vowel bandwidth. Noise detection thresholds were measured in a 2IFC task with an adaptive procedure (Levitt, 1971). Detection thresholds were obtained for noise with spectrum envelope parallel to that of the vowel, and for the same noise containing -6.0-dB spectral notches in either of the following bands: (a) 0.2--0.5 kHz; (b) 0.2--1.0 kHz; (c) 4.2--5.0 kHz; and (d) 4.7--5.0 kHz. Thresholds obtained in three highly trained listeners ranged from -27 to -32 dB (expressed in terms of noise-to-vowel power ratio). Threshold differences between spectral notch conditions were small. The results were compared to predictions of the excitation pattern model proposed by Moore and Glasberg [Hear. Res. 28, 209--225 (1987)]. [Work supported by OCAST-HR4-064.]