Intelligibility Enhancement For Hands-Free Mobile Communication

For mobile telephony in a noisy car environment the hands-free mode is mandatory. Both uplink and downlink communication are much more impaired by the acoustic background noise than in the hand-held mode. Numerous publications deal with the “uplink problem”, while much less attention has been spent on the downlink. Under the influence of noise, the near-end user suffers from an increased listening effort and reduced intelligibility of the far-end speech. Speech intelligibility in the presence of noise has been studied, e.g., in [1], and a solution for the hand-held mode of a mobile phone was proposed, e.g., in [2]. The noise problem in the context of public address systems was investigated, e.g., in [3]. In this contribution, the near-end listening enhancement (NELE) approach of [2] is applied to the hands-free operation of a mobile phone in the car. It maximizes the Speech Intelligibility Index (SII) by spectral modification of the received far-end signal, taking into account the near-end background noise. The interaction between uplink noise-reduction, echo cancellation and downlink NELE is analyzed and the NELE algorithm is modified w.r.t. acoustic constraints. The results are verified by measurements and audio examples.

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