The acceptability of spectrum-preserving and spectrum-destroying transposition to severely hearing-impaired listeners.

Various devices have been constructed to lower the frequency of speech sounds to make them accessible to those with hearing in the low frequencies only. In the present experiment two such devices are compared. One device, the FRED (frequency recoding device) maps the 4-8 kHz region on to the 0-4 kHz region in a way that preserves the spectral pattern of transposed signals. The other device, the Oticon TP 72, converts signals in the 4-8 kHz region into low frequency noise (below 1.5 kHz). Both devices combine transposed information with conventionally amplified speech. It was found that untrained adults with acquired sensory-neural hearing losses opted to supplement conventional amplification with FRED transposition on 365 out of 576 occasions, to improve the clarity of speech sounds. Under the same conditions they opted to use Oticon transposition on significantly fewer (32 out of 576) occasions. Subjective preferences for FRED as opposed to Oticon transposition were also highly significant. It was concluded that for the subject group in question a transposition which preserves the relative spectrum of transposed sounds is initially more acceptable than one which uses high-frequency signals to modulate low-frequency noise.