Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:The uncertainty variances have been computed as a function of the difference between the short time Fourier transform of the signals before and after the waveform processing and pre-emphasis steps of the ETSI-AFE and then propagated through the feature extraction process [12].
Category: