Some reorganization 

I propose to merge Discrete-time signal into this article and also the material in Digital_signal#Discussion that was recently split from Discrete-time signal by . This will put description of the signal that results from sampling in context of the process that creates it. Covering Discrete-time signal comprehensively will result in a lot of unnecessary overlap with this article (Sampling (signal processing)). Removing Digital_signal#Discussion from that artcile will allow Digital signal to be about one topic - the pulse train signals used for digital logic. Digital signal is now part disambiguation and part article which is not good. ~