  We conduct a spectral and timing analysis of GX 339-4 and EXO 1846-031 with
the aim of studying the evolution of Type-C QPOs with spectral parameters. The
high cadence data from Insight-HXMT and NICER allow us to track them. Type-C
QPOs appear at the end of low-hard state and/or hard-intermediate state. The
results reveal that the QPO frequency is closely related to the inner disk
radius and mass accretion rate in the two sources. Such a correlation is nicely
consistent with the dynamic frequency model.
