Table 2.

Input impedance testing

Amplifier	1 Hz	5 Hz	10 Hz	25 Hz	50 Hz
OpBox	0.861 GΩ [0.859, 0.864]	0.866 GΩ [0.861, 0.868]	0.869 GΩ [0.866, 0.872]	0.885 GΩ [0.883, 0.889]	0.902 GΩ [0.899, 0.905]
Grass	0.100 GΩ [0.100, 0.101]	0.101 GΩ [0.101, 0.101]	0.102 GΩ [0.102, 0.103]	0.116 GΩ [0.116, 0.116]	0.204 GΩ [0.204, 0.205]
Intan	2.832 GΩ [1.926, 4.915]	2.301 GΩ [1.570, 2.861]	1.842 GΩ [1.775, 1.888]	1.391 GΩ [1.324, 1.471]	0.959 GΩ [0.901, 1.024]

Input impedance values for each amplifier at various EEG relevant frequencies. Two 3-min recordings were taken of sine wave signals, once using a 0-Ω upper arm resistor (wire) and once using a precision 10-MΩ resistor. Recordings were divided into 20 segments, and the RMS values were calculated for each segment. Ratios between RMS values using the different resistors were used to calculate the input impedances. Data are displayed as median [interquartile range].