Peak

A "peak" measurement is the level (in decibels) of the sample with the highest magnitude within a group of samples.

To measure the peak of a group of samples, the absolute value is taken for each sample and the one with the highest value is the peak.

RMS

An "RMS" measurement (an acronym for Root Mean Square) is the square root of the mean of the squares of a group of samples.

To get an RMS value for a group of samples, each sample value is multiplied by itself (a.k.a. squared - which will make every sample measurement past this point always a positive value), the group of samples is added together and then divided by the number of samples (also known as an "average"), and then the square root of that number is taken.

AES-17

The "AES-17" measurement is identical to the "RMS" measurement, with an additional 3dB added to the final value.

To add 3dB to the sample value (if given in floating point format in a range from -1.0 to +1.0), the value is multiplied by 10^0.15. To multiply it by the square root of 2 is an approximation, and not completely accurate.

Average

The "average" of a group of samples is the sum of the value of the samples divided by the number of samples.

This gives a slightly different value than RMS, but very similar.

Crest Factor

The "crest factor" of a group of samples is the peak of a group of samples divided by the RMS of the same group of samples.

Form Factor

The "Form Factor" of a group of samples is the RMS of a group of samples divided by the average of the same group of samples.

Energy

The "energy" of a group of samples is the sum of the squares of the samples in the group.

When measured across multiple streams, the energy is the average of the energy of the individual streams.