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Promotionsvortrag: Digital Enhancement of Speech Perception in Noisy Environments
In many everyday situations, when people try to listen to speech from a loudspeaker, background noise affects the speech perception. Some applications in which this problem arises are mobile phones, public address systems, car entertainment systems, hearing aids, or head phones. Depending on the application, the speech may either be a recording, or, in case of communication systems, it may come live from a person speaking at the so-called far-end. The location of a listener is called the near-end. Although it is usually not possible to cancel the near-end noise source, the speech perception can be enhanced nevertheless by adaptively pre-processing the loudspeaker signal. To find out in which way the speech should be pre-processed, it is beneficial to know the near-end noise characteristics and take them into account. The knowledge can be gained from a near-end microphone that is located close to the listener. This pre-processing technique is called Near-End Listening Enhancement (NELE). In this talk, several NELE concepts and their capabilities of enhancing the speech perception are described in this talk. Afterwards, a novel computationally very efficient NELE algorithm is presented for real-time processing.
When deploying these enhancement concepts, additional problems may arise depending on the application. Two of them are studied in detail:
- If the near-end loudspeaker and microphone are placed close to each other, which might occur at public address systems for instance, the speech from the loudspeaker is coupled into the near-end microphone as crosstalk and disturbs the estimation of the noise characteristics. An analysis of this arrangement shows that the functionality of the NELE algorithm is strongly affected. As a solution, it is proposed to use a new noise estimation technique, which provides significantly more accurate noise estimates than in comparison to state-of-the-art.
- Especially in the case of mobile communication, it is possible that a noise source is present not only at the near-end, but also at the far-end. Consequently, the speech signal from the far-end is disturbed by noise. Typical mobile phones attenuate the far-end noise by employing techniques of noise reduction (NR) before transmitting the signal to the near-end. At the receiving near-end device, the de-noised speech signal would then be processed by NELE to improve the speech perception, based only on the near-end noise. It is shown that NR and NELE counteract each other, which results in unpleasant speech with strong artifacts. Countermeasures are presented to perform NR and NELE jointly at the near-end or the far-end or within the network.
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