Testing and refining a loudness model for time-varying sounds incorporating binaural inhibition

This paper describes some experimental tests and modifications to a model of loudness for time-varying sounds incorporating the concept of binaural inhibition. Experiment 1 examined the loudness of a 100% sinusoidally amplitude-modulated 1000-Hz sinusoidal carrier as a function of the interaural modulation phase difference (IMPD). The IMPD of the test sound was 90° or 180° and that of the comparison sound was 0°. The level difference between the test and the comparison sounds at the point of equal loudness (the LDEL) was estimated for baseline levels of 30 and 70 dB sound pressure level and modulation rates of 1, 2, 4, 8, 16, and 32 Hz. The LDELs were negative (mean = −1.1 and −1.5 dB for IMPDs of 90° and 180°), indicating that non-zero IMPDs led to increased loudness. The original version of the model predicted the general form of the results, but there were some systematic errors. Modifications to the time constants of the model gave a better fit to the data. Experiment 2 assessed the loudness of unintelligible speech-like signals, generated using a noise vocoder, whose spectra and time pattern differed at the two ears. Both the original and modified models gave good fits to the data.