What are the ranges of values for each audio feature/descriptor? I need to normalize some audio feature measurements I've done with the software Wolfram Mathematica. 

Coming from a non signal processing background, I have some difficulties understanding what several audio features are actually measuring and thus the range of values in which each measurement is expressed.

I can't seem to find any documentation regarding the "physical" range of these descriptors, both in the Wolfram software and the MPEG-7 standard.

This is the list of features analyzed, using the names given to them by Mathematica: 

{"Max", "MaxAbs", "Min", "MinAbs", "MinMax", "MinMaxAbs", "Mean", 
"Median", "StandardDeviation", "Total", "Power", "RMSAmplitude",
"Loudness", "CrestFactor", "Entropy", "LPC",
"PeakToAveragePowerRatio", "TemporalCentroid", "ZeroCrossingRate",
"ZeroCrossings", "FundamentalFrequency", "Formants",
"HighFrequencyContent", "MFCC", "SpectralCentroid", "SpectralCrest",
"SpectralFlatness", "SpectralKurtosis", "SpectralRollOff",
"SpectralSkewness", "SpectralSlope", "SpectralSpread",
"ComplexDomainDistance", "ModifiedKullbackLeibler", "Novelty",
"PhaseDeviation", "SpectralFlux"}


I can suppose some of the ranges, e.g. the one of Spectral Centroid, are similar to the range of the audible spectrum, but I have no clue about the more exotic ones.

Is there any trusted source I can rely on?
Unfortunately, the original standard is not available for free. Furthermore, freely available information on the MPEG-7 descriptors seems to be scarce. Therefore, my recommendation is to get [1] which contains in-depth information about all descriptors, including their computation. Once you understand what each descriptor is supposed to describe, and how it is computed, you'll get an idea about its range of values.

The following resources may also be of interest:


An online computation of a number of MPEG-7 audio descriptors for a wave file


References

[1] H.-G. Kim, N. Moreau, and T. Sikora, MPEG-7 audio and beyond: audio content indexing and retrieval. Chichester, West Sussex, England; Hoboken, NJ, USA: J. Wiley, 2005.