I have this instrument that uses air calibration to remove crosstalk between a drive output and receive input. There seems to be a limit on the amount of crosstalk the instrument can remove under air calibration. I was told that the input frequency was 2kHz (as well as teh drive frequency) but the first opamp in the received path is an amplifiying bandpass filter centered at 2.9 kHz. I was also told that if it was set to exactly 2kHz that sometimes the maximum crosstalk limit that can be removed was exceeded and that 2.9kHz solved this problem. What I would like to know is how is this solving the problem? I can make a link between this bandpass and the crosstalk elimination during air calibration. If it is not something general/fundamental or is application specific then forget I asked. Thank you in advance though.