Noise Debug 101

Noise Intro

Noise Definition:  any unwanted signal that contaminates our signal of interest.  Noise can be in the form of an unwanted signal from a signal source (for example the EEG that is much larger than extra-cellular action potentials) or from an external source.  Noise signals can usually be reduced or eliminated.  There are 5 main types of noise signal contamination:  Conducted, Electrostatically Coupled (voltage coupled), Magnetically Coupled, RF Coupled and Brain Electrode Interface. 

Error Signal:  The difference between the real desired signal and the actual signal recorded.  It is usually caused by aliasing (recorded signal bandwidth greater than 1/2 of the sampling frequency), clipping, or improper signal range for an A/D conversion. 

Ground and Return Path:  The term "Ground" is often confused with a signal's return path.  A signal always flows in a complete loop.  In practical terms for data acquisition there will be two halves of the circuit loop, the signal path (getting the signal from the source to the acquisition input) and the return path (getting the signal back to the signal source).  For most applications the return path is considered "ground".  Note that any noise added to either the signal or return path will usually be added to the desired signal as a noise or error signal. 

The next five Tech Tips will be dedicated to detailing the source and solutions to varying types of noise:  Conducted, Electrostatically coupled (voltage coupled), Magnetically coupled, RF coupled, and Brain Electrode Interface.