Dynamics of the media and music

The dynamics, i.e. the difference between the lowest and the highest level, is an important element of music. However it is important to distinguish the dynamics of the media (CD, vinyl, tape, SACD, digital file) and the dynamics of the track of music itself which can be independent of the media.

Let us start with the dynamics of the media which is related to the technical characteristics of this media.
We have as dynamics for the various supports:

The dynamic values are given as an indication and can vary according to the material and the tapes used. There are also 32-bit and 32-bit floating point digital records (not presented here). They have effectively a dynamic range of more than 186 dB. These formats are used to keep the resolution of the final mix in the studio and to allow file exchanges without conversion. But even the dynamic potential of 24-bit is never fully utilized by the music.

Why do we often find 96 dB for 16 bits and 144 dB for 24 bits? The calculation that is made is a shortcut, in fact, we take 2 to the power of 16 (2^16) and we get 16777216 (that is 20xlog(16777216) = 96 dB), but in reality, the signal is alternating, that is to say that it goes from a value -Vmax to +Vmax with a minimum at 0, to encode the fact that the signal is positive or negative, 1 bit is needed, so there are only 15 bits left to indicate the value which can vary from 0 to VMax, with a VMax worth 2^15 or 32768 which corresponds to 20xlog(32768 ) = 90 dB for 16 bits. For the 24 bits, it is the same principle, we have 23 bits for Vmax, which gives 138 dB for 24 bits.

We thus have a classification with to the left the high resolution digital sources, then to the right the magnetic tape, the CD and to finish the vinyl and the cassette.
This classification represents the dynamic capacity of a support and not the dynamics of the music recorded on this support.

Dynamics of music:

The dynamic range is the difference between the lowest level and the highest level. But, for this measurement, it is not always easy to define the lowest level according to the background noise.
The objective is to find a measure that allows easy comparison of the dynamics between between different pieces of music. We therefore looked for a more representative and simpler measure. The DR (Dynamic Range) is based on the difference between the average RMS (Root Mean Square, measures the average loudness) level and the maximum level (peak). It allows to represent the dynamics of a piece of music with values ranging from 1 to more than 20.
A piece of music is considered to have a low dynamic range if it has a DR of less than 10. It becomes more and more dynamic as the DR increases. Below a DR of 10, the music has generally been processed with a dynamic limiter.

Another method is to use the LUFS value which is the perceived loudness of a song or album (LUFS takes into account the actual loudness in decibels and the way the human ear perceives sound). This value allows to know if the sound level of a song is high or not.

LUFS measures the average loudness of an audio track but not its dynamics. To measure the dynamics, we calculate the difference between the LUFS and the maximum of the track, i.e. the True Peak Level. The LUFS and the True Peak Level are relative to the maximum of the signal at 0dB. These parameters are therefore both negative. A LUFS at -18dB and a True Peak Level at -3dB give a dynamic range of -15 dB (-18dB – -3dB).

This result is independent of the medium, provided that certain measurement conditions are respected. Indeed, for the measurement to be valid, it is necessary to measure only the music and not the interfering noises such as clicks on the vinyl or even other noises of the magnetic tapes.
For its simplicity of use, the DR is used for the measurements of the dynamics of the music during the tests.