Hi, I build mandolins and use Audacity Vers 2.0.5 on Windows XP to record frequencies of components of the instruments when I am shaping them by tapping the component and recording ten or so taps, I them view the Plot Spectrum graph in Analysis, to record the frequency of the major tone. I also record plucking of the individual strings when the instrument is completed to check that there are no or minimal overtones (or undertones). Up until now, I have usually just looked at the graph and can see the major frequency easily and any over and under tones, but notice that the vertical axis of the graph in dB’s shows negative dB values, with what I considered to be the loudest or most prominent frequency to be the smallest negative value (if that makes sense). My question is why are the readings negative dB’s and also sometimes when I look at a “peak”, the graph shows a lower value than listed in the panel below the graph e.g., Peak looks like say -40dB on the graph, but is recorded as a different value in the panel below the graph.
I hope this is clear, I really would like to understand the Plot Spectrum better.