There are two types of noise in time series data, white noise, and red noise.
A noise sequence is a white noise sequence if
To check white noise Fisher’s test is performed. Fisher’s test checks that if a sequence is white noise sequence or not. If the value of Fisher’s test outcome is less than 0.5, the sequence is considered as noise free.
A time series is a red noise sequence if
Red noise has a power spectrum towards low frequencies.