Question: In EVS (Enhanced Voice Services) codec implementation, how does a receiver accurately detect onset frames for each channel in an RTP packet, considering unsynchronized encoders?
Option 1: By solely relying on the Marker bit in the RTP header being set to ‘1’ for all channels.
Option 2: Through monitoring of the Frame Type identifier for each individual channel to identify transitions from DTX (Discontinuous Transmission) to active speech.
Option 3: By deriving the detection from the RTP time stamp, which uniformly indicates onset frames across all channels in a packet.
Option 4: By assuming synchronized VAD (Voice Activity Detection) decisions across all channels due to the nature of EVS encoding.
Explanation: The correct approach for detecting onset frames in each channel involves monitoring the content of the channels, specifically the Frame Type identifier, to accurately identify transitions from DTX to active speech. This method is necessary because encoders are not synchronized, leading to potential differences in VAD decisions across channels. Relying solely on the Marker bit or deriving detection from the RTP time stamp would not provide accurate onset frame identification for each channel. Assuming synchronized VAD decisions is incorrect due to the specified lack of synchronization between encoders.