Signal to Noise

November 9, 2013 in AV Design Tips, The Basics by Sam Davisson

signal-to-noiseI’m still not quite sure why but when I started the basic series with "Power and Grounding" most of the comments, both public and private where that I was setting the stage to talk about audio. Having a solid ground plane affects everything but I’ll concede that in this digital age, it affects audio the most since it is still basically distributed in analog.

The second most requested topic was signal to noise. The signal to noise ratio, or SNR, of a signal is a measurement of the power in the signal fundamental relative to the RMS sum of the energy of all in-band noise components excluding harmonics.

From an integration perspective I never give the SNR (signal to noise ratio) a second thought. The reason being is that IF you have a solid grounding system and IF you’ve built your cables correctly and IF you have minimized the distance of your unbalanced analog audio runs, then the worst case scenerio for SNR (and it’s cousins THD & SND) should be that as the lowest SNR rated equipment specified in the system. In other words, it’s a design consideration not an integration issue. But IF it’s not integrated properly, your going to be able to hear it, even with slightly poor hearing. As a consultant, my specifications do not even require testing for these.

From a design perspective you need to answer the question, for yourself, of how much noise is too much noise for the system in design and then specify products that meet those requirements. For me, if I’m designing a performing arts center or music recording studio then I’m looking at a SNR of 110db or greater. A classroom or conference room, typically a SNR around 75db and a executive board room or auditorium which will support the spoken word, a SNR above 80db.. But these are almost arbitrary numbers that I’ve come up with based on customer interaction and satisfaction. There is no science behind them.

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