1.1 Definition of ScopeThis International Standard defines a Multimedia Content Description Interface, specifying a series of interfaces from system to application level to allow disparate systems to interchange information about multimedia content. Itdescribes the architecture for systems, a language for extensions and specific applications, description tools in theaudio and visual domains, as well as tools that are not specific to audio-visual domains. As a whole, this International Standard encompassing all of the aforementioned components is known as “MPEG-7.” MPEG-7 is divided into eight parts (as defined in the Foreword).This part of the MPEG-7 Standard (Part 4: Audio) specifies description tools that pertain to multimedia in the audio domain. See below for further details of application.This part of the MPEG-7 Standard is intended to be implemented in conjunction with other parts of the standard. In particular, MPEG-7 Part 4: Audio assumes knowledge of Part 2: Description Definition Language (DDL) in its normative syntactic definitions of Descriptors and Description Schemes. This part of the standard also has dependencies upon clauses in Part 5: Multimedia Description Schemes, namely many of the fundamental Description Schemes that extend the basic type capabilities of the DDL.MPEG-7 is an extensible standard. The method to extend the standard beyond the Description Schemes provided in the standard is to define new ones in the DDL, and to make those DSs available with the instantiated descriptions. Further details are available in Part 2. To avoid duplicate functionality with other parts of the standard, the DDL is the only extension facility provided.1.2 Fields of applicationMPEG-7 Part 4: Audio is applicable to all forms of audio content. The encoding format or medium of the said audio is not limited in any way, and may include audio held in an analogue medium such as magnetic tape or optical film.The content of the audio is not limited within or without music, speech, sound effects, soundtracks, or any mixtures thereof.The tools listed in this part of the International Standard are applicable to both audio in isolation and to audio associated with video.The specific tools provided within the Audio portion of the standard are designed to work in conjunction with the Multimedia Description Schemes that apply to both audio and video. Because of the “toolbox” nature of the standard, the most appropriate tools from the different parts of the standard may be mixed, within the constraints of the DDL.The MPEG-7 Audio tools are applicable to two general areas: low-level audio description, in the case of the Audio Framework (clause 5), and application-driven description, in the case of the High Level Tools (clause 6).The Audio Framework tools are applicable to general audio, without regard to the specific content carried by the encoded signal. The Scalable Series provides general capabilities for multi-level sampled data. The Audio Description Framework defines specific descriptors for use with the Scalable Series or with Audio Segments, which has properties inherited from the general Segment described in the Multimedia Description Schemes part of the standard. The Silence Descriptor works with the Segment descriptor, and is applicable across all possible audio signals.The high level description tools are applicable to specific types of content within audio. The specific domains are well documented within the introduction to each sub-clause. The audio domains encompassed by the various MPEG-7 Audio tools are speech, sound effects, musical instruments, melodies within music and general audio recognition. These specialised tools may be employed in conjunction with the other tools within the standard.