1. The 100 kHz filter is a hardware filter and is always applied except for when the "Off" option is selected in the dropdown menu. 

This hardware filter is a Bessel 5th order filter.

2. IIR filters between 40 and 1 kHz are firmware filters, which means, that they are calculated on the FPGA.

3. IIR filters with cut-off frequencies lower then 1 kHz are Software filters. If one of these filters is selected in the dropdown menu, then in addition to the software filter, with the selected cut-off frequency, a firmware filter with 1 kHz cut-off frequency is applied (the type and order of this filter is the same as the software one)

4. AAF (zero-phase distortion) has a cut-off frequency of 80 kHz, if the channel sample rate is equal or above 160 kHz. When a lower sample rate is selected , then the cut-off frequency of the AAF is equal to half the samplign rate of that channel.

Special case: If on a channel, that has a sample rate divider, a IIR filter is applied whose cut-off frequency is greater then 0.4 times the channels sampling rate, then in addition to the selected IIR filter a filter with a cut-off frequency at 0.4 times the sampling rate of the channel is also applied to the filter chain.