A critical specification of an analog input board is its input bandwidth
. This determines the maximum bandwidth of an input signal that can be accurately sampled, regardless of the stated sample rate. For example, if a board has a 100KHz sample rate but a 25KHz bandwidth, you cannot accurately sample a signal with a bandwidth greater than 25KHz.
More importantly, for a multi-channel board, the input bandwidth determines the maximum sample rate achievable when sampling more than one channel at a time. The number of channels sampled times the sample rate per channel cannot exceed the bandwidth. If it does, the input circuit will not be able to keep up with the changes in voltage as the board switches from one channel to the next, resulting in errors that appear as crosstalk.
For example, suppose you have a board with a 50KHz bandwidth and a top sampling rate of 100KHz. You are sampling 5 channels. The maximum sample rate per channel for accurate data is only 10KHz (50KHz bandwidth / 5 channels), not 20KHz (100KHz top sample rate / 5 channels)! If you exceed this sample rate, the input circuit will be slew-rate limited, and you will see crosstalk errors in your data.
Know your board's input bandwidth.