Hearing aid software predictive gain values : How accurate are they ?

There are several ways to assess the electroacoustic characteristics of hearing aids. The most commonly used techniques have been the 2-cc coupler, functional gain, and real-ear probe-microphone measurements. In each of these methods, the actual hearing aid that the person will use is assessed either on that individual, in the cases of functional gain and probe-microphone measurements, or in a standard coupler, the HA-1 or HA-2 2-cc coupler. Now, with the advent of digitally programmable and digital signal processing hearing aids, the clinician is offered a variety of choices for how to view hearing aid performance in the software provided by hearing aid manufacturers. On the programming screen, one can choose to display how the hearing aid is programmed in a number of ways, depending on the manufacturer. Options found in the NOAH programming modules include: (1) 2-cc gain, (2) 2-cc output, (3) 2-cc SPL, (4) 2-cc SPLoGram, (5) insertion gain, (6) simulated insertion gain, (7) KEMAR gain, (8) amplified long-term speech spectrum, (9) ear simulator gain, (10) realear SPLoGram, (11) simulated real-ear SPL, and (12) real-ear aided gain. None of these on-screen representations have been made with the actual hearing aid; rather, they represent simulations based on average and expected performance values.