Department of Communication Sciences and Disorders, University of Pittsburgh, Pittsburgh, PA, USA.
Department of Speech and Hearing Science, Arizona State University, Tempe, AZ, USA.
Ear Hear. 2019 May/Jun;40(3):710-724. doi: 10.1097/AUD.0000000000000653.
"Channel-linked" and "multi-band" front-end automatic gain control (AGC) were examined as alternatives to single-band, channel-unlinked AGC in simulated bilateral cochlear implant (CI) processing. In channel-linked AGC, the same gain control signal was applied to the input signals to both of the two CIs ("channels"). In multi-band AGC, gain control acted independently on each of a number of narrow frequency regions per channel.
Speech intelligibility performance was measured with a single target (to the left, at -15 or -30°) and a single, symmetrically-opposed masker (to the right) at a signal-to-noise ratio (SNR) of -2 decibels. Binaural sentence intelligibility was measured as a function of whether channel linking was present and of the number of AGC bands. Analysis of variance was performed to assess condition effects on percent correct across the two spatial arrangements, both at a high and a low AGC threshold. Acoustic analysis was conducted to compare postcompressed better-ear SNR, interaural differences, and monaural within-band envelope levels across processing conditions.
Analyses of variance indicated significant main effects of both channel linking and number of bands at low threshold, and of channel linking at high threshold. These improvements were accompanied by several acoustic changes. Linked AGC produced a more favorable better-ear SNR and better preserved broadband interaural level difference statistics, but did not reduce dynamic range as much as unlinked AGC. Multi-band AGC sometimes improved better-ear SNR statistics and always improved broadband interaural level difference statistics whenever the AGC channels were unlinked. Multi-band AGC produced output envelope levels that were higher than single-band AGC.
These results favor strategies that incorporate channel-linked AGC and multi-band AGC for bilateral CIs. Linked AGC aids speech intelligibility in spatially separated speech, but reduces the degree to which dynamic range is compressed. Combining multi-band and channel-linked AGC offsets the potential impact of diminished dynamic range with linked AGC without sacrificing the intelligibility gains observed with linked AGC.
“通道链接”和“多频带”前端自动增益控制（AGC）被视为替代单频带、通道非链接 AGC 的方法，用于模拟双侧人工耳蜗（CI）处理。在通道链接 AGC 中，相同的增益控制信号被应用于两个 CI（“通道”）的输入信号。在多频带 AGC 中，增益控制独立作用于每个通道的多个窄频带区域。
使用单个目标（位于左侧，-15 或-30°）和单个对称对侧掩蔽器（位于右侧），在信噪比（SNR）为-2 分贝的情况下测量言语可懂度性能。双耳句子可懂度作为通道链接是否存在以及 AGC 频带数量的函数进行测量。方差分析用于评估两种空间布置中条件对两种空间布置中两种条件的影响，同时评估高和低 AGC 阈值下的条件对两种空间布置中条件的影响。进行声学分析，以比较处理条件下的后压缩较好耳 SNR、耳间差异和单耳频带内包络水平。
方差分析表明，低阈值时通道链接和频带数量都有显著的主效应，高阈值时通道链接也有显著的主效应。这些改进伴随着几个声学变化。链接 AGC 产生了更有利的较好耳 SNR 和更好地保留了宽带耳间水平差统计，但没有像非链接 AGC 那样降低动态范围。多频带 AGC 有时会改善较好耳 SNR 统计，并且只要 AGC 通道是非链接的，总是会改善宽带耳间水平差统计。多频带 AGC 产生的输出包络水平高于单频带 AGC。
这些结果支持采用通道链接 AGC 和多频带 AGC 的双侧 CI 策略。链接 AGC 有助于空间分离语音的言语可懂度，但降低了动态范围压缩的程度。结合多频带和通道链接 AGC 可以抵消与链接 AGC 相关的动态范围缩小的潜在影响，而不会牺牲与链接 AGC 观察到的可懂度增益。
