Dynamic Range Control (DRC) and Music/Speech Control (MSC) Programme–associated data services for DAB W. Hoeg (DBP–Telekom – FTZ) N. Gilchrist (BBC) H. Twietmeyer (IRT) H. Jünger (Jünger Audio) There will always be the need for 1. Introduction broadcasters to apply dynamic range compression to some types of programme material, either because The Eureka 147 Digital Audio Broadcasting of the limitations of the broadcasting (DAB) system [1, 2, 3] provides not only a very medium or because of listeners’ high audio quality for the listener in general, but also includes provision for many additional data requirements. services. Most of these data services are indepen- The Eureka 147 DAB digital audio dent of the audio programme, but some of them are broad casting system enables closely related to the audio signal. The latter form broadcasters to transmit programmes the so–called Programme Associated Data (PAD), with a relatively wide dynamic range, which includes the Dynamic Range Control accompanied by a dynamic range (DRC) System and the Music/Speech loudness control (DRC) signal which the listener Control (MSC) system. Some other special fea- may use to effect unobtrusive tures will be provided by the DAB system to tailor compression of the programme the reproduced audio signal to the individual re- dynamics, if required. A music/speech quirements of each listener in his individual recep- control (MSC) signal, which is also tion environment, and so improve the acceptability transmitted, will enable the listener to of future audio reception in general. balance the loudness of different types of programme according to taste. In order to offer an overview of data services for The techniques used for the optional DAB, a general review is given. This is followed compression of programme dynamics by the basic requirements, the strategy and the in DAB may also be used to control principles of DRC for DAB, based on the require- the dynamic range of programmes ments of Eureka 147, the International Telecom- unobtrusively for conventional Original language: English munication Union (ITU) [2] and the European Manuscript received 2/9/94. Telecommunication Standards Institution [3], to- VHF/FM broadcasting, but without The DAB logo has been registered gether with systems for the real–time implementa- control data being transmitted. by a member of the Eureka 147 – DAB consortium. tion of DRC for DAB. 56 EBU Technical Review Autumn 1994 Hoeg et al. 2. Data facilities in DAB acteristics guarantee that DAB data services will be well suited for reception in cars and portable de- 2.1. Architecture of the DAB vices. A stationary DAB receiver built into a PC ensemble could serve as a data service terminal or be used as a multimedia receiver. Although the DAB system is designed primarily for the broadcasting of audio programmes, its ar- Data services from a small number of service pro- chitecture is intended to offer the greatest flexibil- viders may be distributed as one single DAB en- ity for non–audio applications, so that the best use semble to all private end users, e.g. the population can be made of the limited resources of the RF of a town or of a whole country. Typical applica- spectrum and the overall data capacity of the DAB tions could be the distribution of computer pro- signal. As an international standard the system grammes, computer games, traffic guidance, price must be readily adaptable to specific national or lists, electronic newspapers and weather reports. local needs. It must also be adaptable to future applications, such as multimedia services. – Data as a service component of an audio pro- gramme The ensemble of audio programmes and data ser- Nowadays radio and television programmes offer vices carried by a DAB signal can be described ac- data facilities that are linked (by technical mecha- cording to a hierarchy of three levels: nisms) to the selected programme. Traffic message – The service level telling the listener which ser- information (TMC) and teletext are examples of vices are available. these. In the DAB system, different data service components may be linked either to an audio ser- – The service component level informing the lis- vice or to another data service. By using this option tener of the components which comprise the the programme provider may increase the attrac- service. tion of his programme by offering additional faci- – The channel level. The DAB capacity is parti- lities to his listeners. Applications may include tioned in a set of sub–channels. Each audio ser- textual information on the programme schedule, vice component resides in a sub–channel of its detailed information about the topic addressed by own. A data service component can reside in a the audio, the manuscript of a lecture, maps, still sub–channel of its own as a continuous stream pictures referring to a news report, and travel in- in multiples of 8 kbit/s, segmented in 24 ms formation. Several co–operating programme pro- frames(stream mode), in the so–called Fast viders may share the same service component. All Information Channel (FIC) at low rates, of listeners to the different co–operating programmes 100 bit/s or less, or it can share a sub–channel have access to all of the information. with other data service components in a packet – Basic Service Information (SI) multiplex (packet mode). Like the Radio Data System (RDS) in FM broad- Included in the FIC is the Multiplex Configuration casting, the DAB system offers basic service in- Information (MCI). This comprises all the in- formation (carried in the FIC in machine–readable formation needed to get fast access to every service form) to assist the listener and his receiver to select and its components. The MCI describes in detail a service. It comprises programme service labels how each service component can be accessed (i.e. displayed by the receiver, identification of the pro- in which sub–channel it is to be found), the gross gramme language and programme type, cross ref- and net bit rate, and any other details (e.g. the error erences to other programmes, transmitter identifi- protection scheme). cation for navigation purposes or for geographical selection of information, and automatic control for 2.2.Categories of data in DAB presenting special announcements (e.g. news, traf- fic information). The extent of these SI features The DAB ensemble can contain four different goes far beyond the features of RDS and is capable categories of data: of meeting needs which will evolve in the future. – General data services, independent from other – Programme Associated Data (PAD) data or audio services. Data travelling in the PAD channel is intimately The DAB system offers a flexible transport mecha- related to the audio programme. It is assembled nism (with options for conditional access), that can together with the coded audio in the same DAB be used equally well for non–audio data services. frame, so the time relation established at the source The robustness of the DAB system and its RF char- is maintained throughout the complete DAB trans- EBU Technical Review Autumn 1994 57 Hoeg et al. mission chain. So audio and PAD cannot be subject on the total DAB multiplex and system support to different transmission delays. Therefore PAD is features can be found in [1] and [3]. well suited to time critical data such as DRC data. 3. Dynamic range control Because of the strong relation between audio and (DRC) PAD, the programme associated data can be ac- 3.1. General cessed by the receiver only in conjunction with the audio. The PAD channel consists of a fixed part The dynamic range of an audio programme signal (F–PAD, 2 Bytes per 24 ms frame, i.e. 0.66 kbit/s), (sometimes termed the programme dynamic) is the and optionally of an extended part (X–PAD, com- range between the highest and the lowest useful prising 0, 4, or more than 4 bytes per 24 ms, de- programme signal level. The problems associated pending upon the “free” data capacity in the audio with programmes having a wide dynamic range, frame). The first DAB receivers will be able to and with achieving a satisfactory loudness balance cope with up to 16 kbit/s of PAD. between different parts of the radio programme (such as speech or music) are well known from ex- perience with VHF/FM [4, 5]. In many cases the The X–PAD may include textual information source programme dynamic range may be much about the audio programme (title, schedule) and larger than the available dynamic range of the the actual programme item (title, composer, opus, transmission channel; it may also be much larger artist etc.). Some listeners will be interested in hav- than the usable dynamic range in noisy environ- ing lyrics, song or opera texts simultaneously ments such as cars (the so–called reproduction translated from the original language to the lan- dynamic). The reduction required in the dynamic guage commonly used in the coverage area of the range of the programme may be 10 to 30 dB (or DAB signal. more). Fig. 2 shows the dramatic differences in the reproduction dynamics to be expected (based on The F–PAD can convey codes to identify an item figures given in [6]). In addition, there may be very of music (Universal Product Code, International different requirements in the loudness balance be- Standard Recording Code). However, the main tween music and speech programmes, depending purpose for the F–PAD is to carry time–critical on the interests of the listener and the conditions programme–related data. Transport mechanisms for reproduction [5, 7]. During the last 30 years are defined for controlling additional devices (e.g.