Tech Pills: What signal-to-noise ratio is?

When we have a conversation in a noisy place we hear our interlocutor thanks to the sound waves that he emits when he speaks, but in addition we get all the energy from the other more distant conversations, sometimes they add so much energy that we have to ask our companion to speak louder, that is, to emit more energy to be able to distinguish what he says from the background.

The number of times that our companion's voice is more energetic than ambient noise is what we call the signal-to-noise ratio. Normally the signal-to-noise ratio is given in decibels, a logarithmic scale such that when the energy of the signal is multiplied by 10 with respect to the noise, the decibels would be added 10.

Thanks to the redundancy of our language we're able to understand words that come to us with a negative signal-to-noise ratio, as much as 10 decibels less. In electronic systems the signal-to-noise ratio is always positive, an attempt is made to increase the signal or, if necessary, filter the noise.