Why does it show the level that is lower than -96dB?

[defaultbzlrb0tjf2q5]

Dear Sir, 

I used audition cs6 to open the audio file with 16-bit depth and 16khz sampling rate. Open the window of Frequency Analysis to see it in frequency domain. In the window, the vertical scale is sing along amplitude in dB. For 16-bit depth audio file, the minimum amplitude is -96dB. Why does the Frequency Analysis window show the signal level that is lower than -96dB? 

[SteveG_AudioMasters_]

It can do this if your signal is dithered - the explanation is rather complicated, but dither can resolve signals into what appears to be noise. The other thing to bear in mind is that in the frequency analysis window, any individual frequency will appear to be below -96dB because the noise floor is defined as the noise from all of the individual frequencies in your signal added together. Even though you think that there may be no signal at a given frequency, there is - it's the value of the noise at that frequency. It's the addition of all of that that gives you the overall noise floor value, so what you see when it's all spread out in the Frequency Analysis window will look as though it has a lower noise floor anyway.