Brown, D. K., J. J. Eggermont, and B. P. Kimberley. “The Effect of Age and Stimulus Parameters on the Optimum f2/F1 Ratio for DPOAEs”. Canadian Acoustics, vol. 24, no. 3, Sept. 1996, pp. 78-78, https://jcaa.caa-aca.ca/index.php/jcaa/article/view/1049.