Brammer, A., D. Peterson, M. Cherniack, S. Gullapalli, and R. Crabtree. “Maintaining Speech Intelligibility in Communication Headsets Equipped With Active Noise Control”. Canadian Acoustics, vol. 32, no. 3, Sept. 2004, pp. 132-3, https://jcaa.caa-aca.ca/index.php/jcaa/article/view/1663.