The goal of Magicvinyldigital.net is to provide album reviews across all formats, including immersive audio, based on both listening and technical measurements. Since March 2022, in order to better understand the spatialization of immersive albums, from 4.0 up to Dolby Atmos 9.1.6, a spatialization graph has been added to multichannel versions to better visualize how sound is distributed.
After four years of implementation, the spatialization score (SP) provides a solid indication of how different audio channels are utilized. It is based on an evaluation of sound level distribution across these channels, as defined when this representation was first introduced.
However, after analyzing more than a hundred immersive albums, it became clear that one element was missing: a parameter capable of representing the dynamic aspect of spatialization and its movement through space, in addition to the existing data.
To address this, a new graph will be introduced to represent:
- The variation of spatialization over time, including potential sound movements in space
- The relative position of sound in space (for example, identical sound across all channels is perceived as centered)
- The movement and occupation of 3D space, helping to characterize how the mix uses the available sound field
These elements will make it possible to define a new score, complementing the existing one, to better describe these aspects.
As always, this score is an indicator of Spatial Kinetics (SK), not a measure of its quality. It reflects how dynamically the sound space is used. An immersive mix can therefore be excellent even if it does not achieve the highest score.
This new evaluation is based on a 9.1.6 reference configuration rather than the more commonly used 7.1.4. While the format may eventually evolve toward 22.2, no music content is currently available in that format.
This approach allows Dolby Atmos mixes to be represented in 9.1.6 while supporting all existing formats (7.1.4, 5.1.2, 5.1, 5.0, 4.0), including stereo.
To best represent spatialization, the graph offers a three-dimensional visualization with four available views:
- A top view, showing channel levels similar to the previous model, enhanced with a color gradient from dark blue to white to represent frequencies from low to high
- Side and rear views, allowing analysis of front/back distribution and height usage (including top channels)
- A full 3D view, providing a comprehensive spatial representation
Some examples of the new graph :
The track Dream Within A Dream in 5.1 is a great example of a mix that fully exploits spatialization within a 5.1 setup, with circular movements forming a star-like pattern with multiple branches corresponding to the positions of the sounds. It can also be noted that there is no height information, as none was present in the original source. It can be observed that using the entire space, even without height, allows for an SK of 5.9 (without rendering in the rear surround channel), while the SP, which represents channel usage, is at 3.1 due to the limitation to a reduced number of channels.
The track 5 A.M. by David Gilmour, presented here decoded in 7.1.4, delivers a similar SK (5.9) to the Propaganda track in 5.1, but with a 3D distribution. The sound is less spread across the horizontal plane, but makes greater use of the height channels, adding more volume to the overall spatial representation. The SP value of 6.8 shows a good distribution between the front and rear channels, but with a mix that does not fully utilize the entire sound space in Atmos.
For the track On ne change pas by Céline Dion, we also find an SK of 5.9, with a different spatial distribution and an SP of 5.8, indicating a limited use of all the channels, here decoded in 9.1.6.
For the track Beachcombing by Mark Knopfler and Emmylou Harris, we observe an SP of 7.9, indicating a very good balance of levels between the front and rear channels with decoding in 9.1.6. However, the mix remains front-focused, without sound effects that would occupy more of the surrounding space, which explains its SK of 4.3. This example clearly highlights the value of the SK metric in representing the perceived spatial rendering.
With the track Tapestry by Justin Gray, from the album IMMERSED, which won the Grammy Award for Best Immersive Audio Album, we observe an SP of 8.7 and an SK of 7.5. This is visually confirmed by the extensive use of the sound space, highlighting a highly demonstrative immersive mix.
It’s hard to talk about Atmos mixing without mentioning an example from Steven Wilson, such as his remix of Shout by Tears for Fears. The mix is highly demonstrative and makes full use of all channels, with movements and sound placement surrounding the listener, fully exploiting the soundstage, as shown by the graphs and the SP value of 9.3 and SK of 7.5.
The rating takes into account the total available sound space. Very high utilization corresponds to an SK above 7, while good utilization is defined as an SK greater than or equal to 5. The scale is not linear, but varies according to the cube root of the occupied space. As a result, achieving an SK above 8 is exceptional.
This differs from SP, which compares the distribution of channels between the front, rear (and height). SK is measured over 50 ms intervals, providing a good representation of how the sound space is occupied and utilized. Tests using a 10 ms interval showed slightly higher precision, but with a computation time five times longer. The graph operates across different frequency ranges and allows the reproduction of sound movements. The algorithm is more sensitive to sound motion than to reverberation effects, which are less emphasized. These views illustrate the cumulative movement of sound throughout a track. Some frequencies may overlap and mask others in this representation.
In addition to this cumulative view, a dynamic representation of sound distribution will also be available, as shown in the associated video.
Finally, work is underway to develop a program capable of displaying the 3D spatialization of a track. A VST plugin version is currently in development, and will be available soon.