A received RZ-DPSK signal is guided to an interferometer. Additional constrainment of the catch to prevent it from being forced out of coplanar relationship relative to the fork is achieved by narrowing the outboard extremities of the open mouth formed at the catch end opening of the body member. Based on the comparison, at least one of the audio playback devices is designated as a master device and at least one other of the audio playback devices is designated as a slave device. One embodiment of the mudsaver valve also contains a mechanism whereby the valve may be locked open by an accessory tube whenever a pipe gets stuck and becomes inaccessible, thereby permitting wireline operations through the valve so that the pipe may be freed.