Perception of microphone noise in hearing instruments.

In a well-designed instrument the noise level is reduced until it is dominated by the front end noise. In a hearing instrument this is the microphone noise. This paper examines the perception of noise in a hearing instrument by both normal-hearing and hearing-impaired listeners. The noise levels are specified as input-referred values in one-third octave bands. Two sets of measurements, the just-objectionable level (JOL) and the just-audible level (JAL), were assessed in third octave bands from 250 to 5000 Hz. The data indicated that the use of a subjectively described acceptability of noise, JOL, is an unreliable measure due to a very large variability across listeners. It is recommended that mean values for the noise threshold level, the JAL, be used as a guide in the optimization of microphone noise design.