Abstract: In a pulse code modulation communication system in which in each station the local oscillator frequency is controlled by the difference between the aligner fills at the ends of each link coupled to the particular station, a balanced modifier can be applied periodically to the aligner fills at the ends of a link to make the fills symmetrically disposed about a mid range value and/or a straight modifier can be applied periodically to an aligner fill in the particular station to make the aligner fill equal to the mid range value, the modifiers preventing the establishment of falsely synchronized modes among the oscillators of the system.