Signal to Noise Ratio

I'll take a stab at this. Let's say the signal is only the charged particles (the music on the tape) and the noise is the scraping of the tape over the heads. Everything else in environmental, mechanical, electrical and radio contact with the signal is making noise too but forget about it for simplicity. Ok now imagine making salad dressing. Just olive oil (levels of charged particles) and vinegar (levels of noise). One rides atop the other. In real life they're mixed up, but in a visual sense the signal dominates the noise and rides above it. Ok? Now let's say the whole bottle is filled with dressing to a level called 0dB. How far down (from loud to soft) into the oil can you go until you hit the vinegar? The signal-to-noise ratio tells you. For example, if the ratio is 60dB, you'll hear all the signals that occur from 0dB (the loudest reference) all the way down to 60dB less loud than that. Softer than that, the noise will overcome the signal and obscure its perception. Good luck!

SDCampbell, in your example you say the noise level is 96Db below the signal yet claim that at low signal the noise becomes more apparent. Of course the latter is correct. I merely point out that a signal to noise ratio is a measurement in relation to a reference level of 0 dB, the highest level used in the measurement. In other words I do not believe the ratio expresses an absolute deviation from whatever signal is present, but is only in relation to the highest signal used. Hey, maybe it's only me :-)