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- Dahl, Mattias, et al.
(författare)
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Acoustic Echo and Noise Cancelling using Microphone Arrays
- 1996
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Konferensbidrag (refereegranskat)abstract
- This paper presents a new method to simultaneously perform 20 dB acoustic echo cancellation and 10 dB speech enhancement utilizing an adaptive microphone array. The system is based on a fast and efficient on-site calibration. Primarily intended for handsfree telephones in automobiles, the microphone array system simultaneously emphasizes the near-end talker and suppresses the handsfree loudspeaker and car noise. The method can also be used in other situations such as conventional speaker phones.
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- Grbic, Nedelko, et al.
(författare)
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Subband Acoustic Echo Cancelling using LMS and RLS
- 1999
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The increasing use of modern hands free communication systems such as video conferencing, computer communications, and vehicle mounted cellular telephones brings the demand for high-quality acoustic echo cancellation up to focus. In these applications the echo path which has to be identified typically has long time duration, the order of 100 ms. For this identification the length of the filter will be long. This report evaluates the Normalized Least Mean Square (NLMS) and the Weighted Recursive Least Square (WRLS) algorithms for acoustic echo cancelling using a delayless subband scheme. Subband signal processing has shown to be efficient both when it comes to convergence rate and level of echo suppression. The evaluation is performed for real speech signals sampled from a conversation using a hands free set mounted in an automobile, and a conversation using conference telephony equipment in a conference room. A comparison of subband and fullband algorithms is made both with respect to the computational cost and level of echo suppression. Results show that when the impulse response is very long, i.e. in such environments as conference rooms, the subband approach is beneficial. In a car environment the size of enclosure and damping means that the response is quite short and a conventional echo canceller could perform as well as a subband echo canceller. In the study, finite word length effects have not been considered.
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- Gustafsson, Harald, et al.
(författare)
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Noise Suppression Employing Short Delay Processing
- 1999
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Konferensbidrag (refereegranskat)abstract
- Many telecommunication systems allow only a short delay in the terminal. This restriction stems from the fact that a delay will disturb the conversation. Therefore only a short delay is permissible in noise reduction processing. The well-known spectral subtraction method has been modified to introduce only a short delay and a variance reduced gain function. This modification is accomplished by viewing the spectral subtraction as an FFT filter design method which designs a time-varying filter for each block of data. The design will, however, only give the amplitude function, thus in order to obtain a causal filter a phase must be imposed. The spectral subtraction will not provide any phase information hence a minimum phase is imposed on the filter. The designed filter is transformed to the time-domain and the actual noise reduction filtering will be performed in the time-domain with only a short delay. The proposed method reduces the noise by 10 dB with a maximum processing delay of 7 samples.
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