FIG. 2 further shows that the different synchronized sub-signal flows 3a1, 3a2 and 3b1, 3b2, 3 are merged 12 as according to a desired ratio 11 by processing unit 9, on the basis of input from controller 15, into a modified series of sub-signal flows 51, 52. The desired ratio 11 relates here to a desired volume ratio between the signal flows. 3a1 is merged with 3b1 into sub-signal flow 51, 3a2 with 3b2 into 52. The modified sub-signal flows 51, 52 have related sub-signal flow layers 61, 62, 63, 64. Each modified sub-signal flow comprises the sub-signal flows in the desired volume ratio.
FIG. 2 further shows that the sub-signal flows can be fed out directly from processing unit 9.