Sincronização de sistema de audiometria para detecção de respostas evocada auditiva usando magnitude quadrática da coerência

Abstract

The synchrony among the devices of a signal acquisition system is essential for spectral analyses using the Discrete Fourier Transform (DFT). In cases involving periodic signals, no- coherent sampling results in a shift of the frequency of interest, causing the corresponding bin of this frequency not to match the actual frequency and thus resulting in spectral leakage. This problem is particularly relevant in the detection of evoked responses in the electroencephalogram (EEG) signal when there is no synchronization between the generation of the stimulus signal and the EEG acquisition. Therefore, this work proposes the use of the Magnitude-Squared Coherence as a method to adjust the frequency of auditory stimulation in an audiometry system, ensuring synchronization between the audio generator board and the electroencephalograph. The proposed method was tested with synthetic signals, and then applied to adjust a real system. The results showed that the correction factor found was effective in detecting the auditory evoked response, demonstrating the effective synchronization of the system after the frequency adjustment.