Справочник Пользователя для National Instruments NI 9229E

The NI 9229E/9239E uses a combination of analog and digital 
filtering to provide an accurate representation of in-band signals 
while rejecting out-of-band signals. The filters discriminate 
between signals based on the frequency range, or bandwidth, of 
the signal. The three important bandwidths to consider are the 
passband, the stopband, and the alias-free bandwidth. 

The NI 9229E/9239E represents signals within the passband, as 
quantified primarily by passband flatness and phase nonlinearity. 
All signals that appear in the alias-free bandwidth are either 
unaliased signals or signals that have been filtered by at least 
the amount of the stopband rejection.

The signals within the passband have frequency-dependent gain or 
attenuation. The small amount of variation in gain with respect to 
frequency is called the passband flatness. The digital filters of the 
NI 9229E/9239E adjust the frequency range of the passband to 
match the data rate. Therefore, the amount of gain or attenuation at 
a given frequency depends on the data rate. Figure 6 shows typical 
passband flatness for the NI 9229E/9239E.