I am trying to draw a spectrogram from FFT data I get from audio files. The problem is that I can't figure out is what the yielded power (decibels) are relative to. I'm getting some arbitrary -100db-ish numbers, but I don't understand how I can have them represent a finite intensity-scale.
If I have a gradient which will represent the intensity of these numbers, where silence is black and the maximum is yellow I need to know what the maximum is. I'm really not good in the DSP-area so help would be appreciated.