subsubsection_Multifrequency_scalp_recordings_The__.tex

\subsection{Multifrequency - scalp recordings}
The variation in SNR across frequency, figure \ref{MFSNR}, was not significant  ($P<0.05$), ranging from 44.1 to 45.5 dB.  However, the reduction of current amplitude at frequencies below 200 Hz, reduced the SNR by 1dB compared to subsequent frequencies. The longer term recordings also did not demonstrate any significant frequency dependence ($P<0.05$) in SNR with 41.6 $\pm$ 7.9 dB, 41.4 $\pm$ 8.25 dB and 40.7 $\pm$ 8.2 dB for 0.2 1.2 and 2 kHz respectively. Similarly the drifts 0.74 \%, 0.61 \% 0.68 \% of were also not significantly variable across frequency.