[tebasuna51]

Both are values stored in headers of AC3 and DTS streams.

In DolbyDigital (AC3) streams docs:

Dialogue Normalization
This 5-bit code indicates how far the average dialogue level is below digital 100 percent. Valid values are 1–31. The value of 0 is reserved. The values of 1 to 31 are interpreted as -1 dB to -31 dB with respect to digital 100 percent.

Then with a AC3 DN of -27 the signal must be scaled in -4 dB (-31 - (-27))

In DTS docs:

Dialog Normalisation Parameter

The dialog normalization gain (DNG), in dB, is specified by the encoder operator and is used to directly scale the decoder outputs samples

Show directly the attenuation needed (-4 dB) instead the relative value to -31 in AC3.