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Filtering Problems in BioBench

Primary Software: Other NI Software>>BioBench
Primary Software Version: 1.0
Primary Software Fixed Version: N/A
Secondary Software:

Problem: Digital filtering in BioBench does not appear to be working correctly. For example, if I acquire a 10 Hz sine wave as an input signal (+/-2 Vpp) and apply digital filtering as follows:
  • a) Low Pass (with cutoff frequency = 100Hz) I would expect to see an un-attenuated 10Hz signal, but I get no 10Hz signal.
  • b) High Pass (with cutoff frequency = 100Hz) I would not expect to see an un-attenuated 10Hz signal, but I do.
  • c) Band Pass (low cutoff = 1Hz, high cutoff = 100Hz) I would expect to see an un-attenuated 10Hz signal, but I see no 10Hz signal.
  • d) Band Stop (low cutoff = 1Hz, high cutoff = 100Hz) I would not expect to see an un-attenuated 10Hz signal, I do.


Solution: This is actually a bug in BioBench. The Low Pass filter acts as a High Pass filter and vice versa. Likewise, the Band Pass filter acts as a Band Stop filter and vice versa. To fix this problem you can simply select the High Pass filter option when you want to have a Low Pass filter. Other substitutions would hold for the other types of filters as specified above.

A second, perhaps more desirable solution would be to use an updated version of the BB.llb file. Replace the old BB.llb in your BioBench directory with the new one. This file can be found at the link below and corrects this bug with filtering. Valid filtering ranges for this file are 1 to 99 Hz. This updated file does not support the use of User Events in BioBench, so if you are using User Events you may want to use the workaround mentioned above.

Related Links: KnowledgeBase 24CGFO7Z: BioBench Support Files
BioBench Support


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Report Date: 01/09/2001
Last Updated: 02/27/2003
Document ID: 258BIJ7Z

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