  This note study the soft behavior of Yang-Mills (YM) and bi-adjoint scalar
(BAS) amplitudes at tree level, by using transmutation operators proposed by
Cheung, Shen and Wen. By acting such transmutation operators to gravity
amplitudes in the soft limit, we reproduce universal soft factors of YM
amplitudes at the leading and sub-leading orders, and explain that the
analogous universal soft behavior does not exist at the sub-sub-leading order.
Subsequently, by acting the same operators on YM amplitudes, we obtain the
universal soft factor of BAS amplitudes at the leading order. Furthermore, we
find that a "weaker" version of universal soft behavior of BAS amplitudes holds
at the sub-leading order, if we exclude the special $4$-point case.
