Frequency Lowering Concepts and Issues
Alexander reports that the goal of frequency lowering (FL) is to essentially move (inaudible) high-frequency information to the lower (audible) bandwidth. He states that we (clinicians and researchers) do not yet know enough to predict who will or will not benefit from FL.
The author notes that there are multiple extrinsic factors (and manufacturers) that include signal-processing technologies to accomplish frequency lowering, such as linear frequency compression (AVR), linear frequency transposition (Widex), non-linear frequency compression (Phonak, Unitron), spectral envelope warping (Starkey), and others. However, beyond the technologies themselves, intrinsic factors (of the listener) matter a great deal, too. Intrinsic factors include the ability to learn to interpret new sounds, cognitive ability, age of hearing loss onset, listening experience and more.
Alexander summarizes that when FL does appear beneficial in speech recognition, the benefit is found in fricative consonants with restricted linguistic content and "not all of the individuals in the studies reviewed showed improvement in speech recognition with FL" and "for some listeners, FL negatively affected speech recognition."
He notes that professionals need to understand which specific FL technology is being considered before implementing it, we need to verify (electro-acoustically) that FL has increased audibility and we must validate outcomes to be certain the individual benefits from FL.
For More Information, References, and Recommendations
Alexander JM. (2013) Individual Variability in Recognition of Frequency Lowered Speech. Seminars in Hearing 34(2):86-107.
Ching TYC. (2012) Eds. Wong L, Hickson L ."Hearing Aids For Children." in Evidence-Based Practice in Audiology—Evaluating Interventions for Children and Adults With Hearing Impairment. Plural Publishing.
McDermott H, Henshall K. (2010) The Use of Frequency Compression by Cochlear Implant Recipients with Postoperative Acoustic Hearing. Journal of the American Academy of Audiology 21(6):380-389.
Wolfe J, John A, Schafer E, Nyffelers M, Boretzki M, Caraway T. (2010) Evaluation of Nonlinear Frequency Compression for School-Age Children with Moderate to Moderately-Severe Hearing Loss. Journal of the American Academy of Audiology 21(10):618-628.
Wolfe J, John A, Schafer E, Nyffeler M, Boretzki M, Caraway T, Hudson M. (2011) Long-Term Effects of Non-Linear Frequency Compression for Children with Moderate Hearing Loss. International Journal of Audiology 50:396-404