  We investigate the effects of noise on parameterised quantum circuits using
spectral analysis and classical signal processing tools. For different noise
models, we quantify the additional, higher frequency modes in the output signal
caused by device errors. We show that filtering these noise-induced modes
effectively mitigates device errors. When combined with existing methods, this
yields an improved reconstruction of the noiseless variational landscape.
Moreover, we describe the classical and quantum resource requirements for these
techniques and test their effectiveness for application motivated circuits on
quantum hardware.
