Drawing a Spectrogram off of FFT - what are the decibels relative to? 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.
For audio files you want to use dBFS, dB relative to full scale:

https://en.wikipedia.org/wiki/DBFS