RMS spectrum of observation 2636010101 of Cyg X-1 at Γ ∼ 1.8. The black dashed line shows the total RMS averaged over the 0.06–15 Hz range, which peaks at around 2 keV. The low- (red) and high-frequency (blue dashed line) variability shows a bimodal behavior. The high-frequency variability from L₂ remains constant above ∼2 keV, while the RMS of L₁ drops off. Below roughly 1.5 keV, the variability drops at all frequencies. The remaining variability is dominated by L₁. The gray curve with the scale on the right axis measures the contribution from the accretion disk in the hard state. L₁ peaks at ∼1.7 keV where the disk contributes ∼40% of the flux.