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Acoustics Research Institute of the Austrian Academy of Sciences, Liebiggasse 5, A-1010 Vienna Phone: 043-1-4277-29500 Fax: 043-1-4277-9296 Email: wad@kfs.oeaw.ac.at http//www.kfs.oeaw.ac.at

Sound File Format BWF (2)

BWF covers useful parts of metadata but not sufficient!

BEXT Chunk contains general metadata such as title, originator, archive number etc.

Coding History (part of BEXT chunk) describes the transmission chain of the current sound signal, providing information such as of sound carrier material, recording and playback equipment, analogue-to-digital-converter and digital I/O interface card of the PC.
Format Chunk is used to specify format information as linear PCM, stereo, sample rate and resolution (16...24 bits).
Quality Chunk contains information obtained from the digitisation procedure, such as a protocol of defects in the analogue recording and transmission chain, tape drop-outs, clicks, thumps, hiss, print-through and additional notes (in preparation).

Cue Sheet Chunk provides cue points, tags and segment data as offset, start time and duration of a specific content in the file (in preparation; see also Audio Segmentation and Content Description).

Wave Chunk contains the audio samples of the digitised sound signal.

Example of an Unique Source Identifier (USID):

Generated by a Tascam DA88, S/N 396FG347A, operated by Radiotelevisione Italiana, at time: 12:53:24UDI format: CCOOOSSSSSSSSSSSSHHMMSSRRRRRRRRR

UDI Example: ITRAIDA88396FG347125324098748726

The following BWF file structure is currently supported:

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As has been pointed out, BWF is an advanced real life example for combining sound and (technical) metadata in a comprehensive file format for broadcasting storage and retrieval applications as well as for programme exchange between different partners. One of the outmost advantages of the approach transporting all necessary metadata within the sound files themselves is easy management of sound files and metadata in the LAN and across different hard- and software platforms. For the archive or library starting from scratch, a medium size digitisation project can be evolved on learning by doing and just by implementing a minimum standard as BWF requests. For up to several ten thousands of sound files of a homogenous collection, general purpose computer systems and file archive servers provide file management and browsing tools convenient for use.

Larger collections will not succeed without additional data base management and a specified file system structure. Links from (or to) an existing catalogue have to be updated at regular intervals and sound and metadata should be ”frozen”. In any case, before digitising, libraries and archives should think very carefully about implementing appropriate file naming conventions for sound files and associated documents along content related classification or indexing schemes in order to support effective data retrieval later on.

The current BWF structure is certainly superior when the percentage of metadata associated to sound is small in comparison to the data size of the sound itself. It is applicable when search and browsing is primarily done on the basis of listening to sound data and not by cruising through large volumes of content related metadata. One very useful extension of the BWF concept could be providing appropriate links to recently evolving content description standards as MPEG-7 promises to become.