EFFECT ON THE SPEECH RECEPTION THRESHOLD IN NOISE OF THE RECOVERY-TIME OF THE COMPRESSOR IN THE HIGH-FREQUENCY CHANNEL OF A 2-CHANNEL AID

This paper describes two experiments in a series evaluating and optimi sing a hearing aid incorporating two forms of automatic gain control ( AGC). The first form is a front-end AGC which is normally slow acting and which compensates for variations in the overall level of speech fr om one situation to another. The second form of AGC follows the front- end AGC. The signal is split into two frequency bands, and fast-acting AGC is applied in the upper band only. The bands are then recombined. The two experiments described here were aimed at determining the opti mum value of the recovery time of the AGC in the high-frequency channe l. Speech reception thresholds (SRTs) were measured in the presence of speech-shaped noise as a function of the recovery time, for subjects with mild-to-moderate sensorineural loss. In the first experiment the recovery time was varied over the range 10-80 ms. SRTs tended to be lo west (best) at the shorter recovery times but the effects were small. In the second experiment, the recovery time was varied over the range 5-320 ms. In this case, there was a clear trend for SRTs to increase w ith increasing recovery time. A recovery time of about 20 ms appears t o be optimal.