Sustainability of Digital Formats: Planning for Library of Congress Collections

DAMF, or Dolby Atmos Master File, is a closed and proprietary output package format that supports the surround sound spatial audio system Dolby Atmos, "an immersive audio experience that empowers creators to place discrete audio elements or objects in a three-dimensional sound field, which is not possible in stereo." Stampede Immersive explains that "Dolby Atmos [also known as just Atmos] uses metadata in addition to traditional audio to create an immersive experience for listeners. What this means is that sound is no longer bound to a set amount of speakers in a monitoring environment and is panned using coordinates in 3D space rather than by channel. It also adds the dimension of height to the existing surround plane so that the project really can exist in a 3-dimensional way." While this has many advantages for both the recording industry and consumers, there are also some detractors as explained in an interview on PBS News Hour: How Dolby Atmos promises to change how people experience music and movies (September 11, 2023) between special correspondent for arts and culture, Mike Cerre, and John Couling of Dolby Laboratories: "according to some critics, hearing sounds from different directions can be distracting. Neuroscientist and musician Dr. Daniel Levitin believes it depends more on the nature of the sound and how the technology is used...If there was something outside of our field of vision, a sudden loud noise that's called the startle response, depending on the noise, we might jump. We might turn around. But if they have been there all along as part of the musical piece, just like a humming refrigerator coming from the other room, you habituate to them and they're not alarming."

DAMF is a package composed of three files (as described in Hybrik's Dolby Atmos Tutorial):

• "filename.atmos: The .atmos file is an XML file describing the name of the other two files, how many beds and objects are utilized, the start time (offset), the FFoA (first frame of action, often the same as the starttime), the framerate, and other information.
• filename.atmos.metadata: The .atmos.metadata is an XML file with position (X, Y, and Z coordinates [X-coordinate is measured along the east–west axis, the Y-coordinate is measured along the north–south axis, and the Z-coordinate measures height or elevation]), volume, speaker configuration, and size coordinates for objects over time.
• filename.atmos.audio: The .atmos.audio is a Core Audio File (CAF) of up to 128 tracks. These files are the largest [files in the package]."

As explained Exploring Dolby Atmos and why Metadata Matters, "Dolby Atmos metadata consists of two primary components, Audio Objects and Bed Channels. Audio Objects are individual sound elements, such as an actor’s voice, rainfall, or a car on the highway. Each audio object is accompanied by metadata that specifies its position in the 3D space, its movement trajectory, and other attributes like size and sound characteristics. In addition to audio objects, bed channels are similar to the speakers in a conventional surround sound setup and provide a foundation upon which the audio objects can be placed and moved." Official Dolby Atmos Documentation expands on the implementation with "object audio and their associated metadata are kept on separate buses from the Bed audio. In the end-user's device they are rendered in the correct position for the individual device’s speaker configuration and capability."

Accessibility Features

DAMF is a package of XML and CAF. XML-based formats have good support for accessibility features. According to W3C's XML Accessibility Guidelines, XML-based formats can include features that promote accessibility depending on implementation. CAF's header includes self-identification and specification version number. There are other fields where descriptive metadata can be included, as well as the inclusion of unique identifiers. Comments welcome.