for characterization and implementation of classical feedforward.

The converter box is characterized by a series of probe-tone scattering parameter measurements $S_{ij}(\delta)$, where $i=\mathrm{e},\mathrm{o}$ is the measured port, $j=\mathrm{e},\mathrm{o}$ is the excited port, and $\delta$ is the frequency of the probe relative to the pump [@andrews_bidirectional_2014]. As shown in Fig. \[sparam\]a, when $\Gamma_\mathrm{e} \approx \Gamma_\mathrm{o}$, a dip in microwave reflection occurs near $\delta/2\pi=f_\mathrm{m}$, with a corresponding peak in microwave-to-optical transmission, indicating the absorption of signals in the microwave port and their emission at the optical port. A nearly identical optical-to-microwave transmission signal is also observed. The peak transmission $|t|^2 = 0.55$ corresponds to a conversion efficiency of $\eta = |t|^2/\mathcal{A} = 0.41$, where $\mathcal{A}$ is the independently measured converter gain due to imperfect sideband resolution [@andrews_bidirectional_2014]. The converter bandwidth (measured as the full width at half maximum of the transmission peak) is given by the total linewidth of the optomechanically and electromechanically damped membrane mode, $\Gamma_\mathrm{T} = \Gamma_\mathrm{e} + \Gamma_\mathrm{o} + \gamma_\mathrm{m}$. For comparison, if $\Gamma_\mathrm{e}$ is decreased such that $\Gamma_\mathrm{e} \ll \Gamma_\mathrm{o}$, microwave reflection becomes almost flat, with a value determined by the microwave cavity coupling, and nearly zero power is transmitted. At the same time, a peak is observed 