To understand the physical processes governing accretion discs we can study active galactic nuclei ( AGN ) , X-ray binary systems ( XRBs ) and cataclysmic variables ( CVs ) . It has been shown that XRBs and CVs show similar observational properties such as recurrent outbursts and aperiodic variability . The latter has been extensively studied for XRBs , but only recently have direct phenomenological analogies been found between XRBs and CVs , including the discovery of the rms–flux relation and the optical detection of Fourier-dependent time-lags . We present a Fourier analysis of the well-known CV SS Cyg in quiescence based on data collected at the 4.2–m William Herschel Telescope using ULTRACAM . Light curves in SDSS filters u ^ { \prime } , g ^ { \prime } and r ^ { \prime } were taken simultaneously with sub-second cadence . The high cadence and sensitivity of the camera allow us to study the broad-band noise component of the source in the time range \approx 10000 - 0.5 s ( \approx 10 ^ { -4 } -2 Hz ) . Soft/negative lags with an amplitude \approx 5 s at a time-scale of \approx 250 s were observed , indicating that the emission in the redder bands lags the emission in the bluer bands . This effect could be explained by thermal reprocessing of hard photons in the innermost region of the accretion disc , assuming a high viscosity parameter \alpha > 0.3 , and high irradiation of the disc . Alternatively , it could be associated with the recombination time-scale on the upper layer of the accretions disc .