Sub-dividing the 4-couple Rueda into 2 groups by adding ECHO at the end of a call modifies the partner-changes.
Echo usually starts with the cantante and his opposite leader changing partners through the center … while the other two leaders follow the same command on the next measure. In the picture below, the leaders of the couples on the right and left are beginning to enter the circle to change partners while the north/south leaders have already crossed through the center to pick up a new follower.
If the cantante continues to call while approaching his/her next partner (before the DQN of his/her next partner) then the ECHO modification remains in effect and the circle will continue to be sub-divided, changing partners through the center of the circle. However, if no call is made, then ECHO is cancelled and normal partner changes resume. Note: unlike the CRUZADO call, everyone continues to dance on the same timing.