PSD of double DRW kernels for different parameter ratios. The Bayes ratio resulting from the GP fitting is reported above each panel. In all the panels, the light curves are sampled every 3 d for 10 yr. The power is reported in arbitrary units. Case (a): Similar variability amplitudes but considerably different damping timescales. The test can correctly identify the UBHD (shown as the red square in Figure 4). Case (b): Similar amplitudes and similar damping timescales (shown as the red diamond in Figure 4). Case (c): Considerably different amplitudes but similar damping timescales (shown as the red triangle in Figure 4). Case (d): Considerably different amplitudes and damping timescales (shown as the red circle in Figure 4).