Yes, but only in software. There is one exception: the high pass filter on the new ActiveOne system can be bypassed to achieve a DC response. The decision to choose for fixed filter settings is the result of the increased processing speed of the PCs in the last years. With a typical PC, it is no problem to filter the data provided by our systems (up to 500 kSamples/s) on line. Given this modern processing power, we decided to keep the front-end simple, compact and reliable by eliminating all switches and additional components that would be needed for adjustable filters.

The frequency response of our systems is plotted in the figure below. The low-frequency signals have a lower gain to prevent saturation of the amplifier and ADC on large electrode offset potentials. However, note that the DC signals are not rejected. The low-pass filter is necessary to prevent aliasing effects of high frequency electrode and amplifier noise. We use a 5th order Bessel filter for optimal pulse response (no overshoot). The -3 dB frequency of the filter is placed at 1/4 of the (fixed) sample frequency. The filter provides approx. 20 dB suppression at the Nyquist frequency (half the sample rate). This setting has proved to be a good tradeoff between a maximal analog bandwidth, and minimal additional noise by aliasing.