Binaural recordings of 400 Hz tones with 25 Hz sinusoidal amplitude modulations (0-100% depth) played from a loudspeaker in my dining room. Analyses show that ITD and ILD again resemble ‘ideal’ values before recent reflections arrive. Values then drift and fluctuate due to combinations of the modulations, acoustic reflections and background sounds. Modulations prompt contributions to spatial hearing from cues arising throughout the tones.
Interaural level differences (ILDs) at the times of zero-crossings after passing each recording through a 400 Hz auditory filter (circles in upper panel). Red and blue lines in the lower panel show right and left amplitude envelopes, respectively.
- • ILDs fluctuate broadly prior to when each pure-tone starts (before 0 ms).
- • Values then contract for ~20 ms as amplitude rises, as would occur in a quiet, anechoic, setting.
- • Values next begin to drift and fluctuate after ~20 ms, due to modulations, acoustic reflections and background sounds.
When compared with recordings of pure-tones lacking modulations (greens lines):
- • ILD are seen to skew positively as amplitude declines but skew negatively as amplitude inclines. Deep amplitude throughs therefore prompt substantial increases in ILD variation over time.
- • ILDs coinciding with amplitude peaks attain values closer to those observed at each tone’s onset (before ~20 ms), as would occur in a quiet, anechoic, environment.