Block poly glycols are disclosed. This system and method is useful in alpha-secure key distribution systems comprising a multitude of alpha-secure keying material shares to be controlled, revoked or updated. If no speaker is connected to the output terminal, no test sound is output. One example includes using high directivity, narrow beamwidth antennas and time based markers from a wireless digital communication signal for locating a mobile unit source of radiation. The processor determines an end time associated with the media clip corresponding to a time stamp when the first user input is detected, and a start time associated with a media clip based on the second user input.