The disclosure provides improved processing of optical data by identifying anomalous signals in the electrical data representing the optical data. The improved processing can also include modifying the identified anomalous signal data to provide a truer representation of the optical data. The disclosed processing can be used by various systems and apparatuses for processing spectral data corresponding to the optical data. The improved processing can be used to improve the monitoring of semiconductor processes and, therefore, improve the overall semiconductor processes. In one example, a method of processing spectral data includes: (1) receiving temporally separated spectral data samples, and (2) identifying one or more anomalous signals in an intermediate one of the temporally separated spectral data samples based on at least one preceding and at least one subsequent ones of the spectral data samples.