Frequency-lowering processing to improve speech-in-noise intelligibility in patients with age-related hearing loss

Modern hearing aids use various signal-processing strategies to improve speech intelligibility. In this manuscript, we studied the linear frequency transposition (LFT), a frequency-lowering algorithm, in patients with age-related hearing loss. Frequency-lowering algorithms transpose high-frequency sounds to a lower-frequency band. The study aimed to assess whether LFT could be used as a tool to improve speech intelligibility in patients with a better high-frequency preservation.

The study population consisted of 77 patients (age average 74.8 ± 12.4) wearing hearing aids with an open or tulip coupling system with age-related hearing loss. The unaided air conduction pure tone average (PTA) at 500, 1000, 2000 Hz was 43.5 ± 14.3 dB; the unaided word recognition score (WRS) average was 53.7 ± 12.5%. We compared WRS in all patients with the hearing aid turned on, in "quiet" and using a "pink" and "babble" masking noise. Three hearing aid settings were tested in each acoustic conditions: no transposition (NT), high transposition (HT), and low transposition (LT). "High" and "low" refer to the "start frequency"; all sounds above the start frequency are transposed in a lower-frequency band. When the start frequency was suggested by the fitting software, we called the condition "high transposition"; when the start frequency was set at the lowest possible value provided by the fitting software, we called the condition "low transposition". The quality of the voice was also assessed asking the patient to give a score from 1 to 10, where 10 was the maximum listening comfort [quality of voice score (QVS)].

Collected data were compared for each condition (NT, HT, LT, in quiet, pink noise and babble noise) and no statistically significant differences were found in WRS and QVS (quiet WRS p = 0.07, pink noise WRS p = 0.18, babble noise WRS p = 0.11, QVS p = 0.91). We selected 33 patients with a better WRS in babble noise using transposition (high and low). In this group, the age was significantly lower than patients who did not use transposition (p = 0.01).

Linear frequency transposition is not useful to improve speech-in-noise intelligibility in patients with age-related hearing loss. Despite that no statistically significant differences were found, younger people could get advantages from the LFT when babble noise disturbs the listening of speech. The use of FL algorithm as a way to improve speech intelligibility in noisy environments should be always considered.