Most engineers are familiar with the concept of signal to noise ratio: maximizing signal and minimizing noise is a governing principle in communication technology design. What some may not know is that the concept can also be used in information and document design, where it is also considered a governing principle, especially in the design of visuals.
Garr Reynolds’ popular blog, Presentation Zen, explores the concept and its application to slide design in two popular blog posts from 2007. In the first, Reynolds uses the Universal Principles of Design to define the concept for information designers as “the ratio of relevant to irrelevant information in a display,” and asserts that “the highest possible signal-to-noise ratio is desirable in information design,” just as it would be in radio or electronic communication design .
3D textures, portions of visuals impossible to see, and parts of visuals not discussed in a presentation or paper constitute superfluous or irrelevant information in a display, and can be removed. In The Visual Display of Quantitative Information (1983), Edward Tufte famously coined the term “chartjunk” to refer to these unnecessary elements: “simply conventional graphic paraphernalia routinely added to every display that passes by: over-busy grid lines and excess ticks, redundant representations of the simplest data, the debris of computer plotting, and many of the devices generating design variation .” Tufte’s strongest example comes from visualizations of data on Cancer Survival Rates, each of which have been adorned by a multitude of unnecessary visual elements. 
Garr Reynolds’ contribution to this discussion is his challenge to the concept that all non-essential elements constitute “noise,” and his idea that emotional impact of visual elements can contribute significantly to meaning. A second entry on Signal to Noise ratio walks through a Whole Foods case study in which Reynolds challenges the definition of noise, and argues that elements that may be noisy for some might add value for others. These are components of visuals that though they might not present essential information, might provide what I would term “constructive interference.” Consider, for example the differences in the two final slides on arable land in organic production, one with just the essential data, the other with an image that evokes the need to be concerned about the lack of organic arable land in North America .
Summary: Signal to Noise Ratio is good governing principle for slide design, but what constitutes noise may vary amongst audience members. In designing slides, follow Reynolds’ advice that “ideas like SNR are good principles, but not rules to be blindly followed,” and that it is only “one principle among many to be considered when creating visual messages.”
 G. Reynolds. “Signal-to-Noise ratio and the elimination of the nonessential,” March 12, 2007. Accessed, July 15th, 2014. http://www.presentationzen.com/presentationzen/2007/03/signaltonoise_r.html
 G. Reynolds. “Slide design: signal vs. noise (redux),” March 12, 2007. Accessed, July 15th, 2014. http://www.presentationzen.com/presentationzen/2007/03/a_few_weeks_ago.html
 E. Tufte. “Cancer survival rates: tables, slopegraphs, barcharts,” Accessed, July 15th, 2014. http://www.edwardtufte.com/bboard/q-and-a-fetch-msg?msg_id=0000Jr