What is the formula for calculating interaural attenuation (IA)? a) IA = Sound Pressure Level (SPL) - Threshold of Hearing (TOH) b) IA = Interaural Time Difference (ITD) + Interaural Level Difference (ILD) c) IA = Bone Conduction Threshold - Air Conduction Threshold d) IA = Frequency of Sound / Speed of Sound in Air