  We present the spectro-timing analysis of the black hole binary system GX
339-4 using AstroSat data extracted at the beginning of outbursts in 2017 and
2019. The joint spectral fitting of LAXPC and SXT data revealed that the source
was in a faint low/hard state for both 2017 and 2019 observations with a nearly
equal photon index of $\sim$1.57 and $\sim$1.58 and with Eddington ratio,
$L/L_{Edd}$, of 0.0011 and 0.0046 respectively. The addition of a reflection
component into the spectral modelling improved the fit ($\Delta\chi^2$
$\approx~6$ for 2017 and $\Delta\chi^2$ $\approx~7$ for 2019), pointing towards
the presence of weak reflection features arising due to irradiation of the
accretion disk. The power density spectrum (PDS) consisted of strong
band-limited noise with a break at low frequencies, described with a
combination of few zero-centered Lorentzian. The fitting revealed a
low-frequency break at $\sim$6~mHz for 2017 and at $\sim$11~mHz for 2019
observation, whose detection is validated by results from independent detectors
(LAXPCs and SXT). The break frequency is roughly consistent with results
obtained from earlier observations that showed an evolution of the frequency
with flux, which is in accordance with the truncated disk model. Associating
the break frequency with viscous time scale of the accretion disk, we estimated
a truncation radius of $\sim$93 and $\sim$61 gravitational radius for 2017 and
2019 observation, respectively.
