Abstract
Background
High-frequency hearing loss is one of the challenges for accurate hearing. One method of amplification toward improved detection and discrimination of high frequencies is through lowering of high frequencies to a lower-frequency hearing region. Frequency compression (FC) or frequency transposition (FT) can be used for individuals with different configurations of hearing impairment, such as steeply sloping and high-frequency hearing loss (containing high-frequency dead regions).
Objective
The purpose of this review was to compare the effects of FC and FT on the speech recognition abilities of people with hearing impairment.
Patients and methods
This study is a systematic review of previous investigations carried out to test the efficacy of frequency-lowering algorithms (i.e. FC or FT) in improving the detection of high frequencies. The concept of FC and FT depends on enhancement of speech recognition in patients suffering from high-frequency hearing loss. In this review, compression shifting and frequency transposition were compared on the basis of improvements in the audibility of high frequency sound to improve the outstanding and acceptance level of speech.
Conclusion
It can be concluded from this review that both FC and FT are useful in people with high-frequency hearing loss. FC has a potential role in recognition of monosyllabic words, consonants, and sentences in the presence of background noise. In contrast, FT facilitates detection of fricatives that ultimately leads to improvement in the discrimination of consonants. Throughout the literature, only one study has compared both FT and FC using various speech tests to evaluate the performance of different hearing instruments. Therefore, further studies addressing the benefits of both modalities of hearing aids with a more standardized outcome measure for both adult and pediatric patients are required.