  We report on a detailed analysis of the so-called ~1 Hz quasi-periodic
oscillation (QPO) in the eclipsing and dipping neutron-star low-mass X-ray
binary EXO 0748-676. This type of QPO has previously been shown to have a
geometric origin. Our study focuses on the evolution of the QPO as the source
moves through the color-color diagram, in which it traces out an
atoll-source-like track. The QPO frequency increases from ~0.4 Hz in the hard
state to ~25 Hz as the source approaches the soft state. Combining power
spectra based on QPO frequency reveals additional features that strongly
resemble those seen in non-dipping/eclipsing atoll sources. We show that the
low-frequency QPOs in atoll sources and the ~1 Hz QPO in EXO 0748-676 follow
similar relations with respect to the noise components in their power spectra.
We conclude that the frequencies of both types of QPOs are likely set by (the
same) precession of a misaligned inner accretion disk. For high-inclination
systems, like EXO 0748-676, this results in modulations of the neutron-star
emission due to obscuration or scattering, while for lower-inclination systems
the modulations likely arise from relativistic Doppler boosting and
light-bending effects.
