Table 6.
Clincial Question 2: Comparison of amplitude compression WDRC versus linear amplification on speech recognition outcomes at average input levels (55–70 dB).
| Citation | Condition | Compression settings | Stimuli | Open/closed set | Presentation level/SNR | Effect size [95% CI]a | p |
|---|---|---|---|---|---|---|---|
| Boothroyd et al. (1988)b | WDRC | Threshold: NR Attack time: NR Release time: NR Ratio: prelimiting gains increased by the amount by which the participant’s dynamic range of hearing fell short of 30 dB Volume control: NR |
Nonsense syllables: All contrasts | Closed | NR | rpb = −.14 [−.77, .63]c | p < .01 (favors linear) |
| Final consonant voice | Closed | NR | rpb = −.26 [−.82, .54]c | p < .01 (favors linear) | |||
| Vowel height | Closed | NR | rpb = −.35 [−.85, .47]c | p < .01 (favors linear) | |||
| Duration | Closed | NR | rpb = −.04 [−.72, .68]c | ns | |||
| Intonation | Closed | NR | rpb = −.03 [−.72, .69]c | ns | |||
| Vowel place | Closed | NR | rpb = −.07 [−.74, .67]c | ns | |||
| Initial consonant continuance | Closed | NR NR |
rpb = −.28 [−.82, .53]c | p < .01 (favors linear) | |||
| Linear CL | Threshold: NR Attack time: 2 ms Release time: preamplifier = 1 s; second compression-limiter = 20 ms Ratio: NR Volume control: NR |
Initial consonant voice | Closed | rpb = .11 [−.64, .76]c | ns | ||
| Initial consonant place | Closed | NR | rpb = .11 [−.64, .76]c | ns | |||
| Christensen (1999) | WDRC | Threshold: Low: 45–50 dB SPL Attack time: 5 ms Release time: 50 ms Ratio: Variable:1.1:1–7.8:1 Volume control: listener unable to adjust during testing |
Bisyllabic spondaic words | Open | 65 dB SPL/quiet, +5, +10 SNR | NR/NC | ns across SNRs |
| Passages | Open | 65 dB SPL/quiet, +5, +10 SNR | NR/NC | ns across SNRs | |||
| Linear CL | Threshold: High: 75 dB Attack time: 5 ms Release time: adjustable up to 1 s Ratio: 8:1 Volume control: listener unable to adjust during testing |
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| Linear PC | Threshold: none Attack/release time: instantaneous Ratio: none Volume control: listener unable to adjust during testing |
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| Gou et al. (2002) | WDRC | Threshold: 40 dB Attack time: NR Release time: NR Ratio: NR Volume control: AGC |
Words (discrimination of phonological oppositions) | Closed | 65 dB SPL/quiet | NR/NC | p < .01 (favors WDRC) |
| Monosyllabic words | Closed | 65 dB SPL/quiet | NR/NC | ns | |||
| Bisyllabic words | Closed | 65 dB SPL/quiet | NR/NC | ns | |||
| Own linear | Threshold: NR Attack time: NR Release time: NR Ratio: NR Volume control: fixed |
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| Jenstad et al. (1999) | WDRC | Threshold: 45 dB Attack time: 10 ms Release time: 200 ms Ratio: varied by DSL prescription Volume control: listener unable to adjust |
Nonsense words | Closed | 60 dB SPL/quiet (avg. speech at 1 m) | NR/NC | ns |
| Sentences | Open | 60 dB SPL/quiet (avg. speech at 1 m) | NR/NC | ns | |||
| Linear | Threshold: NR Attack time: NR Release time: NR Ratio: NR Volume control: listener unable to adjust |
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| Marriage & Moore (2003) | WDRC | Threshold: 50–55 dB SPL Attack time: 5 ms Release time: 30 ms Ratio: varied between 1.7: 1 to 2.7: 1 Volume control: NR |
Words (consonant confusion task) (severe and profound HL) | Closed | 60, 50 dBA/quiet, +10 SNR | r = .78 [.07, .97]d |
p = .021 (favors WDRC) Compression × Presentation Level: ns |
| Monosyllabic words (severe HL) | Open | 60, 50 dBA/quiet, +10 SNR | r = .999d,e |
p < .001 (favors WDRC) Compression × Presentation Level: ns |
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| Linear | NR | ||||||
| Marriage et al. (2005) | WDRC | Threshold: 40 dB at 200 Hz; 25 dB at 4400 Hz Attack time: 5 ms Release time: 30 ms Ratio: 1.2:1 to 3.0:1 Volume control: NR |
Monosyllabic words (profound HL) | Closed | 65 dBA/quiet | NR/NC |
p < .002 (WDRC > linear CL) ns (WDRC vs. linear PC) |
| Words (profound HL) | Open | 65 dBA/quiet | NR/NC | ns | |||
| Common phrases | Open | 65 dBA/quiet | NR/NC | ns | |||
| Sentences SNR | Open | In 60 dB modulated noise | NR/NC | ns | |||
| Linear CL | Threshold: high Attack time: 0.5 ms Release time: 50 ms Ratio: NR Volume control: NR |
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| Linear PC | Threshold: high Attack time: 0.5 ms Release time: 5 ms Ratio: NR Volume control: NR |
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| Stelmachowicz et al. (1995) | WDRC | NR | Nonsense syllables | Closed | 65 dB SPL | NR/NC | ns |
| Linear | NR (conditions assessed using 2 different devices) |
a
Positive effect sizes indicate that the direction of the effect favors WDRC; negative effect sizes indicate that the direction of the effect favors linear amplification.
b
One outlier removed.
c
Effect size rpb (point-biserial correlation coefficient), calculated from individual participant data provided in the study.
d
Effect size r calculated using F statistic and degrees of freedom provided in the study.
e
Confidence intervals were not calculable.