As explained in section 5.2.2, a cross-correlation based algorithm was proposed and implemented in the RT06s system in order to select the optimum channel to act as reference channel in the beamforming system. By automatically selecting this channel the system becomes independent of the human assignment of the SDM channel, which NIST selects in the RT datasets and which was used as reference in previous versions of the system.
Table 6.6 shows the results of the RT06s system (with automatic selection) or the same system but using the SDM channel as reference. By automatic selection of the optimum channel the results become slightly worse both in SNR and DER. Although the DER of the development set is almost equal to the hand-picked reference channel case, in the test set there is a decrease in DER performance of 1.87% relative. By considering the development results, it is preferable and more robust to use the automatic selection of the reference channel, as it then becomes possible to use this system in areas other than the RT evaluation data, where there might not be any prior information on which microphone to select as the reference channel.