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This paper proposes two audio mixing algorithms in software based Multipoint Control Unit (MCU) using Automatic Gain Controller. The objectives of the proposed algorithms include performing selective mixing, minimizing audio clipping, assigning higher amplitude priority to the loudest speaker and ensuring a smooth transition as the primary speaker changes from one participant to another. The proposed algorithms are able to suppress unexpected signal spikes by considering previously computed gain value(s) in the calculation of the current gain. The proposed algorithms are also able to mix multiple VoIP packets for up to eight conference participants within 150μs, which is well below the default RTP audio packet timeframe of 20ms. The proposed mixing algorithms are integrated with the audio decoder and encoder modules to complete theMCU system. Experiments were carried out to verify the basic performances of the proposed mixing algorithms.
Date of Conference: 6-9 Dec. 2010