subsection_Resistor_Phantom_Frequency_response__.tex

\subsection{Resistor Phantom - Frequency response}
Both EEG systems both contain sinc filters used for anti-aliasing, with cut off frequencies quoted at 1.7 kHz and 7.5 kHz for the BioSemi and ActiCHamp respectively. In both systems, frequency response correlated with the gain of the respective filter, figure \ref{freqresp}, with a mean error of 0.07 \% and 0.09 \% for frequencies below the cut off for the BioSemi and actiCHamp respectively. The amplitude decrease was 1.86 mV V or 21.0\% from 20 Hz to 2 kHz for the BioSemi and 0.57 mV or 6.26\% for the actiCHamp across the same range. Across the full 20 kHz range the total decrease was 9.15 mV or  99.6 \%. Below these cut-off frequencies, there was no significant change in mean SNR across frequency, with 68.9 dB $\pm$ 9.42 dB for the BioSemi and 71.4 dB $\pm$ 12.6 dB for the actiCHamp.