We have to admit that, as analog designers, we tend to get scared when the word “noise” pops up in front of us. As an almost immediate side effect, the concepts of denoising, cleaning, and filtering come to our perfectionist minds. But noise, though by definition unwanted signals, can also be among our most precious debugging tools arsenal — and a valuable source of information for diagnostic purposes.
There are plenty of examples where noise signals are relevant for the application. They range from very simple cases, like injecting a 50/60 Hz signal into an audio amplifier using the tip of the finger, to very complex and math-filled ones, like detecting, analyzing, and locating the source of cosmic rays.
True random numbers play a key role in the field of communications security. Unfortunately, most number generation algorithms produce only pseudo-random series. How do we generate a true sequence of random numbers? We have to rely on stochastic physical processes for ensuring randomness. Thermal and atmospheric noises have found their way into this process.
White and colored noise generators are particularly useful in ambient noise blocking and radio jamming. In cry analysis, the presence or absence of specific formants and distortions may provide clues about a baby's health. Fluctuations of current or potential associated with corrosion processes are useful for determining corrosion types and speed.
Vibration analysis has proved a very effective technique for early detection of bearing and structural damages due to mechanical stress. In my years working as a designer and programmer for smart card manufacturing machines, I've realized that, most of the time, having the best-in-class software debugging tools and being a skilled and experienced programmer are not enough when addressing situations like the one illustrated below.
When it comes to debugging mechanically complex systems, one very valuable skill is the ability to discriminate noises that deviate from the expected, normal-operation noise. Having a trained, noise-friendly ear is a real advantage and a must-have component of the machine hardware debugging arsenal.
For example, two conditions in a paper/chip ticket converting machine are shown below — normal operation noise and noise produced when paper strip breaks.
Noise can be our ally and not just our most feared analog enemy. Have you ever found applications where noise has not been merely an unwanted signal? What other types of noise would be signals of interest?