Benefits of linear amplification and multichannel compression for speech comprehension in backgrounds with spectral and temporal dips

People with cochlear hearing loss have markedly higher speech-receptions th resholds (SRTs) than normal for speech presented in background sounds with spectral and/or temporal dips. This article examines the extent to which SR Ts can be improved by linear amplification with appropriate frequency-respo nse shaping, and by fast-acting wide-dynamic-range compression amplificatio n with one, two, four, or eight channels. Eighteen elderly subjects with mo derate to severe hearing loss were tested. SRTs for sentences were measured for four background sounds, presented at a nominal level (prior to amplifi cation) of 65 dB SPL: (1) A single female talker, digitally filtered so tha t the long-term average spectrum matched that of the target speech; (2) a n oise with the same average spectrum as the target speech, but with the temp oral envelope of the single talker; (3) a noise with the same overall spect ral shape as the target speech, but filtered so as to have 4 equivalent-rec tangular-bandwidth (ERB) wide spectral notches at several frequencies; (4) a noise with both spectral and temporal dips obtained by applying the tempo ral envelope of a single talker to speech-shaped noise [as in (2)] and then filtering that noise [as in (3)]. Mean SRTs were 5-6 dB lower (better) in all of the conditions with amplification than for unaided listening. SRTs w ere significantly lower for the systems with one-, four-, and eight-channel compression than for linear amplification, although the benefit, averaged across subjects, was typically only 0.5 to 0.9 dB. The lowest mean SRT (-9, 9 dB, expressed as a speech-to-background ratio) was obtained for noise (4) and the system with eight-channel compression. This is about 6 dB worse th an for elderly subjects with near-normal hearing, when tested without ampli fication. It is concluded that amplification, and especially fast-acting co mpression amplification, can improve the ability to understand speech in ba ckground sounds with spectral and temporal dips, but it does not restore pe rformance to normal. (C) 1999 Acoustical Society of America. [S0001-4966(99 )05401-6].