Abstract
Audio metadata are an essential tool that supports control and management of systems that create, transmit, describe, manage, and store digital audio. Throughout the lifecycle of digital audio objects—pre-production, acquisition and production, post-production, distribution, storage, transmission, and archiving—metadata “describe the attributes of a resource, characterize resource relationships, and support resource discovery, management, and effective use” (Vellucci, 1999). Technical and structural metadata enable audio in devices and software applications; descriptive metadata provide context. Metadata also relate and incorporate audio in a multimedia environment resulting in profound effects on conception, reception, and consumption.
TopBackground
Analog sound recording technologies had been in use for over a century when the Compact Disc Digital Audio (CD-DA) technology emerged in the late 1970s following breakthroughs in signal processing and the optical medium. Audio continued to be produced in a mixture of analog and digital systems consisting of single-purpose devices designed for recording and producing audio to be transmitted in either analog or digital form. The production system was largely determined by the transmission medium––wire, wax cylinder, shellac disc, vinyl disc, magnetic tape, broadcast, optical disc––each requiring an assortment of specialty equipment, typically supplied by a single manufacturer. In such vertically integrated systems, controls and switches that supplied parameters and characteristics (metadata) to the audio were generally integrated in the hardware. Where metadata were specified and shared, the necessity for interoperability was limited to the devices immediately before and after in the production chain.
As digital signal processing technologies evolved, the proliferation of recording formats, compression methods, and media formats made it no longer sensible to build a separate integrated system for each device combination. In such a mixed production environment, devices need to be able to pass along and recognize standardized metadata throughout the production process. For several decades since the 1970s, the broadcast industry attempted to standardize metadata within device categories to allow for interchangeable equipment for each step of the production. But demands for higher flexibility and broader scope mounted as increasing prevalence of computer software and data networks shifted production workflow and transmission toward a distributed model. The industry was compelled to re-conceive use of metadata in not only audio, but also video production in a digital environment where data and content would be stored and transmitted in the form of computer files. These files, ideally, would encapsulate all necessary metadata, interoperable through the production chain, regardless of media format or equipment.
Key Terms in this Chapter
Metadata Standards: Specifications or definitions that establish common meaning, usage, and interpretation of metadata.
Technical Metadata: Describe the state, the creation process, and the digital characteristics of a resource.
Digital Audio: Digital coding of analog audio signals.
Descriptive Metadata: Describe a resource for the purpose of identification, discovery, and retrieval.
Metadata Schemas: Structures that establish and define data elements, the relationships between them, and the rules governing their use.
Semantic Audio: The extraction of symbols and meaning related to audio, including speech and non-speech content.
Embedded Metadata: Metadata that are stored in the same file that carries the object described by the metadata.
Extensible Markup Language: A markup language that defines a set of rules for encoding textual data recommended for semantic web publishing.