  A quiet point, an operating point of pump-resonance detuning that minimizes
frequency fluctuation due to nonlinear effects inside a resonator, has been
employed for phase noise reduction of a soliton Kerr microresonator frequency
comb (microcomb). Naturally, it is expected that the use of the point will also
improve performances of a microcomb in terms of frequency stability and
faithfulness in a phase locked loop. In this study, we experimentally
investigate the effect in a microcomb with a repetition frequency of 300~GHz.
We obtain a lowest fractional frequency instability at a quiet point of
$1.5\times 10^{-9}$ at 1 second, which is 44 times lower than free-running
instability. Phase-locking of a microcomb to a stabilized fiber comb is
demonstrated to evaluate performance in a feedback loop, where in-loop-limited
relative fractional frequency instability between the microcomb and the fiber
comb of $6.8 \times 10^{-13}$ is obtained as an indicator of the stability
limitation.
