Double-evoked otoacoustic emissions. I. Measurement theory and nonlinear coherence

An evoked otoacoustic emission (OAE) measurement technique is proposed to better control for probe distortion. Each double-evoking (2E) stimulus sequence includes three, equal-duration subsequences defined as follows: s(1)(t) is a single chirp or click, s(2)(t)=epsilon s(1)(t-tau) is a copy of sl with relative amplitude epsilon and delay tau, and s(12)(t)=s(1)(t)+s(2)(t) is the superposition of the first two stimuli. The pressure response to each subsequence is p(1), p(2), and p(12), respectively. The double chirp-evoked distortion product (2ChDP) and double click-evoked otoacoustic emission (2CEOAE) are defined by p(D)=p(12)-(p(1)+p(2)). The 2ChDP response may be time compressed to analyze as an equivalent 2CEOAE response. The 2E response family provides a complementary representation between DP measurements and double click-evoked OAE measurements. A technique based on nonlinear coherence quantifies random noise in terms of a nonlinear signal-to-noise ratio. (C) 1998 Acoustical Society of America.