Dynamic range compression serves different purposes in the music and hearing-aid industries. In the music industry, it is used to make music louder and more attractive to normal-hearing listeners. In the hearing-aid industry, it is used to map the variable dynamic range of acoustic signals to the reduced dynamic range of hearing-impaired listeners. Hence, hearing-aided listeners will typically receive a dual dose of compression when listening to recorded music. The present study involved an acoustic analysis of dynamic range across a cross section of recorded music as well as a perceptual study comparing the efficacy of different compression schemes. The acoustic analysis revealed that the dynamic range of samples from popular genres, such as rock or rap, was generally smaller than the dynamic range of samples from classical genres, such as opera and orchestra. By comparison, the dynamic range of speech, based on recordings of monologues in quiet, was larger than the dynamic range of all music genres tested. The perceptual study compared the effect of the prescription rule NAL-NL2 with a semicompressive and a linear scheme. Music subjected to linear processing had the highest ratings for dynamics and quality, followed by the semicompressive and the NAL-NL2 setting. These findings advise against NAL-NL2 as a prescription rule for recorded music and recommend linear settings.

The AMP test revealed differences in a wide range of music perceptual abilities between NH and HI listeners. The recognition of meter was more difficult for HI listeners when the listening task was based on frequency discrimination. The HI group was less sensitive to changes in harmony and had more difficulties with distinguishing melodies in a background of music. In addition, the thresholds to discriminate timbre were significantly higher for the HI group in brightness and spectral irregularity dimensions. The AMP test can be used as a research tool to further investigate music perception with hearing aids and compare the benefit of different music processing strategies for the HI listener. Future testing will involve larger samples with the inclusion of hearing aided conditions allowing for the establishment of norms so that the test might be appropriate for use in clinical practice.

A novel algorithm for frequency lowering in music was developed and experimentally tested in hearing-impaired listeners. Harmonic frequency lowering (HFL) combines frequency transposition and frequency compression to preserve the harmonic content of music stimuli. Listeners were asked to make judgments regarding detail and sound quality in music stimuli. Stimuli were presented under different signal processing conditions: original, low-pass filtered, HFL, and nonlinear frequency compressed. Results showed that participants reported perceiving the most detail in the HFL condition. In addition, there was no difference in sound quality across conditions.

A new series of tests has been designed to assess the effectiveness of hearing aids for the perception of music. Within each subtest, discrimination thresholds for low-level acoustic dimensions are determined adaptively using a 2AFC method within the context of a musical judgment regarding melody, harmony, timbre or meter. The presented test stimuli are synthesized and either unprocessed or processed by different hearing aid signal processing algorithms before being played back via loudspeaker. The battery will be used to evaluate different hearing aid algorithms with regard to their benefit for functional hearing in music. A group of six normal hearing control participants (6.7 dB HL) and five hearing impaired participants (34 dB HL) each performed the melody subtest and the harmony subtest twice. The hearing impaired subjects had higher discrimination thresholds than the control group. A comparison of the results from both administrations suggests that these two subtests have good test-retest reliability.

No abstract