Pure tone vs. Complex Stimuli

Pure tone stimuli used in conventional audiometry under insert or TDH style earphones are sufficient in providing frequency specific information for testing but in sound field audiometry additional complications exist which could introduce measurement variability.   

In sound field audiometry, sound is transmitted into a reverberant field.  If the signal transmitted in this environment is a pure tone stimulus, standing waves will occur which will prevent the ability to obtain reliable results.  The SPL in a reverberant sound field will not be able to sustain uniformity if the subject moves and will be unable to maintain a stable signal if small shifts in frequency exist (Walker et al 1984, Morgan et al 1979).     

The solution to the above problem is to use complex stimuli such as warble tones.  A complex tone simply implies that more than the signal contains more than one frequency component.  The rationale for using complex stimuli is that they contain energy at a number of frequencies around the nominal/center frequency and this leads to a more uniform field because of the averaging of intensity that occurs across the frequency range covered by the stimulus.  Because of this effect, a complex stimulus will be relatively unaffected by a null in the sound field if it has significant energy within a frequency band which is wider than the null.

**To learn more about calibrating and measurement variability in sound field testing click here

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