Non-linear signal processing in digital hearing aids

Three different non-linear digital signal processing algorithms were develo ped: LinEar, DynEar and RangeEar. All three provided individual frequency s haping via a seven-band low-power filterbank and compression in two channel s. RangeEar and DynEar used wide dynamic range syllabic compression in the low-frequency (LF) channel, while LinEar used compression limiting. in the high frequency (HF) channel. RangeEar used a slow-acting automatic volume c ontrol, while DynEar and LinEar used compression limiting. Wearable digital signal processing-based experimental instruments were used to evaluate the fitting algorithms under real world conditions with experienced hearing ai d users. Evaluation included laboratory testing of speech recognition in no ise and questionnaires on sound quality ratings. Results did not indicate o ne general good-fur-all algorithm, but different algorithms resulting in pr eference and performance depending on the hearing loss configuration. Prefe rence for any of the new algorithms could be predicted based on auditory dy namic range measurements. It was hypothesized that the different preference s were affected by different susceptibility to masking of HF sounds by ampl ified LF sounds.