Further Elaboration: You might ask this question to try and understand the low frequency response to determine if the Geode amplifiers effectively have a flat response from DC up. Does the Geode go down to DC for example?

Answer: We apply anti-alias filters to the data to prevent out of band noise from being introduced into the data.

The filters are set with a corner frequency at ¾ of the Nyquist frequency (1/2 the sampling frequency) for almost all of the sampling frequencies. When we sample at 1.5625 uS, the Nyquist frequency is 32kHz and the filters are set at 20 kHz, because of limitations of our electronics.

There are two single-pole filters: one analog and one digital. The analog filter is a simple RC filter with 1uF +/-5% and 100kOhm +/- 1%. We short out the capacitor in the conversion process. The digital filter is software controlled when the option is registered, so it can be switched in or out in the field. It is an IIR Butterworth with a -3dB corner at 0.9Hz for 48ksps sampling, and 0.6Hz at all the lower sample rates.

Also, we offer software and hardware options to modify the low end frequency response of the Geode.

Low-end bandwidth modification:

  • 1.5 Hz, P/N 28311-37.......................$1,000
  • 0.6 Hz, P/N 28147-01.............$400/8-ch
  • DC, P/Ns 28147-02, 28311-37..................... $1,000 per system plus $400/8-ch