The picture to emerge from the analysis is clear. The mean AC gain is maximal at nearly 40 dB for the audiometric frequencies of 0.25, 0.5, and 1 kHz. The mean AC gain at any given time after operation decreases with increasing frequency, at least for frequencies of > or = 1 kHz. For any frequency there is, with few exceptions, a significant decrease in the AC gain from one time period to the next.