is broadly applicable to two-mode signal processing devices in which transmission occurs through a noisy intermediary mode. It also complements recent theoretical work proposing adaptive control for quantum transducers [@rakhubovsky_squeezer_2016; @zhang_quantum_2018].

We will consider classical and quantum feedforward protocols in a microwave-mechanical-optical converter in which the mechanical element is thermally occupied (Fig. \[schematic1\]a). The noise emitted from each port contains a redundant record of the mechanical oscillator’s thermally driven motion. During operation, the signal to be converted is injected into the microwave port and an ancilla state is injected into the optical port. The upconverted signal, with noise added, is emitted from the optical port. The ancilla state, contaminated with the same added noise, is emitted from the microwave port. Measuring the downconverted ancilla and feeding forward to the propagating optical mode can remove this correlated added noise.

Classical and quantum feedforward protocols are distinguished by the choice of ancilla. Simply choosing the ancilla to be optical vacuum causes zero-point fluctuations (vacuum noise) to be fed forward along with the thermal noise. In this case, although thermal noise may be completely removed, vacuum noise from the ancilla is necessarily written onto the upconverted signal. Choosing vacuum as the ancilla therefore 