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Analog Angle

Can Adding Noise Actually Improve System Performance?

Bill Schweber
GSKrasle
GSKrasle
8/6/2018 1:18:00 PM
User Rank
Artist
Re: Natural noise analysis
I have seen a lot of applications of "noise" (as in "dithering") to improve performance; it's something that is (unfortunately) not covered in curricula where frictionless vacuums are "ideal" and usable ways to deal with the real world are deferred to those (unnecessarily) painful learning experiences we all suffer when first we leave the ivory towers.

In image-processing, especially compression, dithering conceals edges introduced when dynamic range or resolution is reduced. But I use it all the time to increase ADC resolution, especially in oscilloscopes, where 8-bits is usual, with 10-bits only seldom available. Obviously, that limits the number of steps available, so it is only natural to invoke the built-in averaging function to seek more resolution. That often works, but not when you have a beautiful smooth NOISELESS signal. Adding noise, so that when the REAL signal is half-way between steps it gives half-density to each of the adjacent steps (or at least equally-distributed among steps on either side) would be ideal, but what kind of noise gives that result? Well, a sawtooth or triangle does, and is easy to subtract- or filter-out if necessary. A sine is pretty good, and even easier to remove. 

A a good example of MECHANICAL dithering (to overcome stiction, like the case mentioned in the article) applies to d'Arsonval and similar meters: either pulses are introduced into the signal itself or through a separate mechanism (vibrator). This takes the place of the user tapping the meter to make sure it doesn't stick.  

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vbiancomano
vbiancomano
8/5/2018 3:05:27 PM
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Blogger
Natural noise analysis
Apart from the discussion of how to use noise to advantage, it always struck me odd that engineers by and large, myself included, report that the reconstructed analog output of a digitally encoded voice signal (e.g., PCM) actually sounds better than the analog source input! All this without knowingly performing any tricks with circuitry. Perception, or reality? Either way, what happens here?

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