Question
Can speech noise be used to evaluate digital hearing aids? If so, should the noise reduction circuits be turned off before the measurements are made? In the case of basic digital hearing instruments, where the noise circuit can't be turned off -- what then? Can REM be done accurately? What is the best stimulus to use to do REM on digital hearings aids?
Answer
Q: Can speech noise be used to evaluate digital hearing aids?
A: Speech noise can certainly be used to evaluate digital hearing aids. There are many different types of ''speech'' noise. For example, the test signal may be a modulated speech noise that mimics the prosody of real speech and there are systems that allow a live voice to be used as the stimulus. Of course, if the speech noise selected does not have the necessary modulation characteristics there will be a reduction in the gain measured by the amount of noise reduction the instrument possesses.
Q: If so, should the noise reduction circuits be turned off before the measurements are made?
A: If your intention is to determine ''real world'' gain, then yes. If your speech noise test signal is not modulated, the noise reduction should indeed, be turned off. The time the noise reduction takes to activate varies by manufacturer.
Q: In the case of basic digital hearing instruments, where the noise circuit can't be turned off -- what then? Can REM be done accurately?
A: If a given hearing aid does not have the ability to have it's noise reduction turned off, and if you do not have a system that possesses modulated speech noise, there would still be practical REM measurements you could make. All REM manufacturers have a ''digital speech'' signal that can be used and in most cases the ability exists to upgrade your current system.
Q: What is the best stimulus to use to do REM on digital hearings aids?
A: The best signal to use with digital hearing aids varies with the measurement you want to make. The digital speech (ICRA) signal was developed for measuring real world gain values in an instrument with noise reduction active. I often say the digital speech signal is ''backward compatible'' because you can use it on any level of technology from linear to advanced digital instruments.
Carol Thomas Bryant, Au.D.
Carol Thomas Bryant is the Manager of Training and Education for Madsen / GN Otometrics. She is responsible for developing advanced technology courses on behalf of Madsen as well as training programs for Madsen's full line of diagnostic instrumentation. Carol is Madsen's primary clinical interface for new U.S. products and software development.
Carol has spent the last ten years in the clinical environment, the last seven as Audiology Director for Tuscaloosa Ear Nose & Throat Center, P.C., in Tuscaloosa Alabama. She received her Au.D. from the University of Florida in Gainesville, her M.C.D. from Auburn University and completed graduate externships at Baylor College of Medicine in the Neurosensory Center of Methodist Hospital under the direction of Dr. James Jerger. Carol' s background before entering Audiology was a B.S. in education and public school experience.
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