Why so many different scales?


For historical purposes, mainly.


Different manufacturers as well as different countries came up with different ways to measure the levels of audio. Almost all of them are based on the decibel, whether directly or indirectly, but they may use different numbers for different level measurements.


At the baseline, when it comes to digital audio, there is one basic measurement, which is dBFS or decibel full scale. This equates to 0dB being the same as ±1.0 in floating point digital format with a 1:1 decibel-to-scale-mark scale. This is the most honest of all the scales in the digital realm.


That being said, what follows are the other common audio scales.


VU


The VU scale (VU is an acronym for "Volume Unit") is offset -14dB from dBFS.


0dBFS is equal to +14 on the VU scale

0 on the VU scale is the same as -14dBFS


The scale increments are also in decibels.


UK (BBC) PPM


The UK (BBC) PPM (PPM is an acronym for Peak Program Meter) is probably the most unusual of all the scales.


The meter has 7 "marks", all at intervals of 4dB between -30dBFS and -6dBFS:


Mark 1 = -30dBFS

Mark 2 = -26dBFS

Mark 3 = -22dBFS

Mark 4 = -18dBFS

Mark 5 = -14dBFS

Mark 6 = -10dBFS

Mark 7 = -6dBFS


EBU PPM


The EBU PPM scale (PPM is an acronym for "Peak Program Meter") is offset -18dB from dBFS, and the 0dB level is labelled as "test".


0dBFS is equal to +18 on the EBU PPM scale

"test" on the EBU PPM scale is the same as -18dBFS


The scale increments are also in decibels, and the major marks above "test" are in intervals of 4dB


DIN PPM


The DIN PPM scale (PPM is an acronym for "Peak Program Meter") is offset -9dB from dBFS.


0dBFS is equal to +9 on the DIN PPM scale

0 on the DIN PPM scale is the same as -9dBFS


The scale increments are also in decibels.


Nordic PPM


The Nordic PPM scale (PPM is an acronym for "Peak Program Meter") is offset -18dB from dBFS, and 0 is labelled as "test"


0dBFS is equal to +18 on the Nordic PPM scale

"test" on the Nordic PPM scale is the same as -18dBFS


The scale increments are also in decibels, and the major marks above "test" are in intervals of 6dB.


K-20


The K-20 scale (named after Bob Katz, its inventor) is offset -20dB from dBFS.


0dBFS is equal to +20 on the K-20 scale

0 on the K-20 scale is the same as -20dBFS


The scale increments are also in decibels.


K-14


The K-14 scale (named after Bob Katz, its inventor) is offset -14dB from dBFS.


0dBFS is equal to +14 on the K-14 scale

0 on the K-14 scale is the same as -14dBFS


The scale increments are also in decibels.


K-12


The K-12 scale (named after Bob Katz, its inventor) is offset -12dB from dBFS.

0dBFS is equal to +12 on the K-12 scale
0 on the K-12 scale is the same as -12dBFS

The scale increments are also in decibels.