Tsing Hua Univ, Dept Engn Phys, Beijing 100084, Peoples R China
; Tsing Hua Univ, Ctr Astrophys, Beijing 100084, Peoples R China
; Tsing Hua Univ, Dept Phys, Beijing 100084, Peoples R China
; Chinese Acad Sci, Inst High Energy Phys, Particle Astrophys Lab, Beijing, Peoples R China
A technique for calculation of variability coherence at different timescales performed directly in the time domain is introduced. Simulations are made to compare the coherence spectrum derived by the time-domain technique with the coherence function derived by Fourier analysis. The results indicate that in comparison with the Fourier analysis the time-domain technique is more powerful for revealing signal coherence in noisy data. We apply the time-domain technique to real data of the black hole binaries Cygnus X-1 and GX 339-4 and compare the results with their Fourier coherence spectra.