The algorithm of the ensemble pulsar time based on the optimal Wiener filtration method has been constructed . This algorithm allows the separation of the contributions to the post-fit pulsar timing residuals of the atomic clock and pulsar itself . Filters were designed with the use of the cross- and autocovariance functions of the timing residuals . The method has been applied to the timing data of millisecond pulsars PSR B1855+09 and PSR B1937+21 and allowed the filtering out of the atomic scale component from the pulsar data . Direct comparison of the terrestrial time TT ( BIPM06 ) and the ensemble pulsar time PT _ { ens } revealed that fractional instability of TT ( BIPM06 ) –PT _ { ens } is equal to \sigma _ { z } = ( 0.8 \pm 1.9 ) \cdot 10 ^ { -15 } . Based on the \sigma _ { z } statistics of TT ( BIPM06 ) –PT _ { ens } a new limit of the energy density of the gravitational wave background was calculated to be equal to \Omega _ { g } h ^ { 2 } \sim 3 \cdot 10 ^ { -9 } .