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Abstract
The purpose of the questionnaire survey was to ascertain the current status of warble-tone in audiometers. Of 29 audiometer manufacturers, 24 replied (82.7%) representing 9 different countries.
The questionnaire was divided into 3 sections. In part I information was requested concerning the current status of warble-tone. The results showed that only 6 manufacturers (25.0%) currently offer the warble-tone stimulus.
In part II specific information was sought from those currently offering warble-tone or contemplating its inclusion in the near future. The replies of the respondents indicated that the frequency deviation varies from approximately +0.2% above the base frequency to as high as ±10% around the base frequency. The modulation rate ranges from 2/sec to as high as 10/sc. Audiometer manufacturers accomplish the warble-tone in essentially two different ways; either by modulating around the base frequency or above the base frequency, with the wave form of the warbled signal either sinusoidal or rectangular. The signal is not calibrated to any single accepted, current standard. With respect to its intended use (by the manufacturers), the warble-tone was most often suggested for threshold measurements in sound-field or under earphones.
Part III of the survey sought to determine the future status of warble-tone from the manufacturers’ point of view. In addition to the 6 manufacturers currently producing warble-tone, 3 others indicated that they expect to include it within 1–4 years. Five were undecided and 8 replied that they did not expect to incorporate it in their units.
The warble-tone is included in those audiometers which are generally the most versatile (discrete frequency clinical and/or research audiometers). Also, there appears to be a trend toward more manufacturers offering it as an additional stimulus. The primary deterrent (from the manufacturers’ point of view) seems to be that the warble-tone's significance has not been adequately determined and that there has been little or no demand for it as an auditory stimulus.
Finally, there is a dearth of research concerning the most appropriate warble-tone stimulus parameters to be employed in threshold determination. This problem must be resolved before warble-tone audiometry can seriously be considered as part of the audiologist's clinical armamentarium.