A method of eliminating a disturbing component from a periodic signal. The method includes the steps performing at least two measurements on the signal at two distinct instants, calculating the parameters of the disturbing component on the basis of the measurements, and subtracting the disturbing component from the signal. The invention is applicable to making an electronic capacitor voltage transformer comprising a capacitor divider constituted by a high tension capacitor and a low tension capacitor. The transformer includes a microprocessor programmed to perform the above method on the signal from the low tension capacitor.

An electromagnetic-noise protection circuit for protecting an electrical device, which processes wanted signals, comprises a sensor which senses the presence of ambient electromagnetic noise from which the electrical device is to be protected, and a filter coupled to the sensor and intermitting the operation of the electrical device in time periods during which the sensor senses the presence of the ambient electromagnetic noise. The sensor can include a discriminator which discriminates wanted signals affected by ambient electromagnetic noise from wanted signals not affected by ambient electromagnetic noise. The discriminator can be implemented as a window comparator comprising at least three triggers and a logical gate and producing a logic output signal indicating if the input signal is either below a certain lower threshold or beyond a certain upper threshold.

The method of reducing contamination of electrical signals recorded in the presence of repeated interference contamination comprises obtaining an electrical signal recorded in the presence of a contaminating signal, and detecting a timing signal that occurs at a fixed time point during the electrical signal relative to the onset of the contaminating signal. The electrical signal is digitized, wherein the digitizing begins with the timing signal. A plurality of digitized electrical signals is analyzed, wherein the electrical signals are synchronized with respect to the timing signal, to obtain an estimated contaminating signal that is subtracted from the digitized electrical signal. This method can be used with electrophysiological signals, such as EEG, ECG, EMG and galvanic skin response, and for elimination of noise associated with concurrently used methods such as MRI. The method of noise reduction is applicable to recordings of other electrical signals, including audio recordings.