Low average signal (4)
I believe the answer is:
mean
I believe this is a triple definition!
'low' is the first definition.
(both can mean nasty)
'average' is the second definition.
(type of average)
'signal' is the third definition.
(thesaurus)
(Other definitions for mean that I've seen before include "Intend; not generous" , "The average could be miserly" , "Type of average" , "Intend; stingy" , "Average or mingy" .)