Why are the dB numbers (on the Y axis) negative?
This is because dB, (or deciBel, named after Alexander Bell) is a relative measure of sound level, meaning it is compared to some standard. Really, you can make that standard anything you want. Sound cards tend to have the capability of accepting at most plus or minus 1 volt without ‘clipping’. So I use that as the peak, or zero dB, and all other values are relative to that. So a value of -10 dB means that it is 10 dB down from the largest measurable value, 0 dB, or 1 volt.
