1. A method of noisy signal analysis carried out by a processor, comprising: (a) setting a threshold, a first step level and a second step level of a step function to be a predetermined threshold value, a first identity value and a second identity value respectively, so that said step function transforms each signal in a signal group to said first identity value; (b) starting from said predetermined threshold value, changing said threshold of said step function and transforming each signal in said signal group with said step function iteratively, until said threshold reaches a first threshold value so that said step function transforms a signal in said signal group to said second identity value; and (c) starting from said first threshold value, changing said threshold of said step function and transforming each signal in said signal group with said step function iteratively, until said threshold reaches a second threshold value so that said step function transforms all signals in said signal group to said second identity value, wherein the range of said signal group is bounded between said first threshold value and said second threshold value.