Design and calibration of a portable high-frequency audiometer

Assessment of high-frequency hearing in the frequency range from 8–20 kHz has been shown to have important clinical applications. It can be used to predict future hearing loss at lower speech frequencies, to monitor the effects of ototoxic drugs, and to assist in the use of speech translation hearing aids. Early detection and monitoring of high-frequency hearing can be used to prevent further hearing impairment. We have developed a unique, portable instrument which meets the technically difficult electroacoustic requirements. These include the design of an attenuator, amplifier, and oscillator with at least 120-dB signal-to-noise ratio, development of a pulse modulator circuit which can present tones with fixed rise and fall times, and calibration procedures for both the electronics and transducer. The transducer used in this unit is a professional earphone with 130-dB dynamic range but other transducers may be substituted. A second masking channel provides a warble tone which tracks the center frequency of the test stimuli. Preliminary testing with 25 young adults shows a test-retest repeatability of approximately 10 dB at each frequency over the entire frequency range.