Figure 1. The waveforms used to elicit and detect speech-DPOAEs. A, B, The spectrogram of the voiced parts of a male speech signal (A) or a female speech signal (B) shows the harmonic structure, with a fundamental frequency and many higher harmonics (note that the colormap represents lower power as dark and higher power as white). C, D, The waveforms used to elicit and to detect the speech-DPOAEs to the male voice (C) and to the female voice (D). A, C, We measure speech-DPOAEs related to the male voice by constructing waveforms
(red line) and
(purple line) that oscillate at the 9th and 11th harmonics of the fundamental frequency of the speech signal, respectively. The lower-sideband speech-DPOAE then emerges at the 7th harmonic and is measured through cross-correlation with the corresponding waveform
(dashed red line). B, D, The speech-DPOAEs related to the female voice are elicited by waveforms
(red line) and
(purple line) that correspond to the 6th and 8th harmonics. The speech-DPOAE is found at the 4th harmonic, we measure it through the waveform
(dashed red line). E, In our experiment, we presented subjects with speech stimuli to the left ear. The speech stimuli were either a single voice or two competing voices, a male and a female one. Two waveforms
and
that were derived from one of the speech stimuli were presented to the right ear. The microphone signal
was recorded from the right ear as well, and the speech-DPOAE was derived from this recording.