Optimum pre-Crescendo elevation derived as that which equalizes the correction gain between the pre-Crescendo and the post-Crescendo for an input level of 30 dBHL.
30 dBHL was chosen as being the least significant sound level in recordings which average around 77 dBHL. This should correspond to the ambient noise level in an empty auditorium.
H_el_pre = 8.6 dB + 0.58 * H_el – ((H_el – 50) / 30)^2
E.g., for H_el = 60 dB, H_el_pre = 43.3 dB