  Sun-as-a-star spectroscopic characteristics of solar flares can be used as a
benchmark for the detection and analyses of stellar flares. Here, we study the
Sun-as-a-star properties of an X1.0 solar flare using high-resolution
spectroscopic data obtained by the Chinese $\mathrm{H} \alpha$ Solar Explorer
(CHASE). A noise reduction algorithm based on discrete Fourier transformation
is first employed to enhance the signal-to-noise ratio of the space-integral
$\mathrm{H} \alpha$ spectrum with a focus on its typical characteristics. For
the flare of interest, we find that the average $\mathrm{H} \alpha$ profile
displays a strong emission at the line center and an obvious line broadening.
It also presents a clear red asymmetry, corresponding to a redshift velocity of
around $50 \ \mathrm{km \ s^{-1}}$ that slightly decreases with time,
consistent with previous results. Furthermore, we study how the size of the
space-integral region affects the characteristics of the flare Sun-as-a-star
$\mathrm{H} \alpha$ profile. It is found that although the redshift velocity
calculated from the $\mathrm{H} \alpha$ profile remains unchanged, the
detectability of the characteristics weakens as the space-integral region
becomes large. An upper limit for the size of the target region where the red
asymmetry is detectable is estimated. It is also found that the intensity in
$\mathrm{H} \alpha$ profiles, measured by the equivalent widths of the spectra,
are significantly underestimated if the $\mathrm{H} \alpha$ spectra are further
averaged in the time domain.
