Editing Digital Audio Broadcasting (section)

==DAB and AM/FM compared==
{{More citations needed section|date=June 2023}}
Traditionally, radio programmes were broadcast on different frequencies via [[AM broadcasting|AM]] and [[FM broadcasting|FM]], and the radio had to be tuned into each frequency as needed. This used up a comparatively large amount of spectrum for a relatively small number of stations, limiting listening choice. DAB is a digital radio broadcasting system that, through the application of [[multiplexing]] and compression, combines multiple audio streams onto a relatively narrow band centred on a single broadcast frequency called a [[DAB ensemble]].

Within an overall target bit rate for the DAB ensemble, individual stations can be allocated different bit rates. The number of channels within a DAB ensemble can be increased by lowering average bit rates, but at the expense of the quality of streams. Error correction under the DAB standard makes the signal more robust but reduces the total bit rate available for streams.

===FM HD Radio versus DAB===
DAB broadcasts a single multiplex that is approximately 1.5&nbsp;MHz wide (≈1,184 kilobits per second). That multiplex is then subdivided into multiple digital streams of between 9 and 12 programs. In contrast, FM [[HD Radio]] adds its digital carriers to the traditional 270 kilohertz-wide analog channels, with capability of up to 300&nbsp;kbit/s per station (pure digital mode). The full bandwidth of the hybrid mode approaches 400&nbsp;kHz.

The first generation DAB uses the [[MPEG-1 Audio Layer II]] (MP2) audio codec, which has less efficient compression than newer codecs. The typical bitrate for DAB stereo programs is only 128&nbsp;kbit/s or less and as a result most radio stations on DAB have a lower sound quality than FM, prompting complaints from listeners.<ref>{{cite web |url=http://wo.uio.no/as/WebObjects/theses.woa/wa/these?WORKID=52348 |last=Holm |first=Sverre |publisher=Digitale Utgivelser ved UiO |title=Lydkvalitetet i DAB digitalradio |year=2007 |access-date=3 January 2009 |url-status=dead |archive-url=https://web.archive.org/web/20080501073857/http://wo.uio.no/as/WebObjects/theses.woa/wa/these?WORKID=52348 |archive-date=1 May 2008}} ([[Nynorsk|Norwegian]]).</ref> As with DAB+ or [[T-DMB]] in Europe, FM HD Radio uses a codec based upon the [[MPEG-4]] [[HE-AAC|HE]]-[[LC-AAC|AAC]] standard.

HD Radio is a proprietary system from [[iBiquity|iBiquity Digital Corporation]], a subsidiary of [[DTS (sound system)|DTS, Inc.]] since 2015, which is itself owned by [[Xperi|Xperi Corporation]] since 2016. DAB is an open standard deposited at ETSI.

===Use of frequency spectrum and transmitter sites===
DAB can give substantially higher [[spectral efficiency]], measured in programmes per MHz and per transmitter site, than analogue systems. In many places, this has led to an increase in the number of stations available to listeners, especially outside of the major urban areas. This can be further improved with DAB+ which uses a much more efficient codec, allowing a lower bitrate per channel with little to no loss in quality. If some stations transmit in mono, their bitrate can be reduced compared to stereo broadcasts, further improving the efficiency.

For example, analog FM requires 0.2&nbsp;MHz per programme. The [[frequency reuse]] factor in most countries is approximately 15 for stereo transmissions (with lesser factors for mono FM networks), meaning (in the case of stereo FM) that only one out of 15 transmitter sites can use the same channel frequency without problems with [[co-channel interference]], i.e. cross-talk. Assuming a total availability of 102 FM channels at a bandwidth of 0.2&nbsp;MHz over the Band II spectrum of 87.5 to 108.0&nbsp;MHz, an average of 102/15 = 6.8 radio channels are possible on each transmitter site (plus lower-power local transmitters causing less interference). This results in a [[system spectral efficiency]] of 1 / 15 / (0.2&nbsp;MHz) = 0.30 programmes/transmitter/MHz. DAB with 192&nbsp;kbit/s codec requires 1.536&nbsp;MHz * 192&nbsp;kbit/s / 1,136&nbsp;kbit/s = 0.26&nbsp;MHz per audio programme. The frequency reuse factor for local programmes and multi-frequency broadcasting networks ([[multi-frequency network|MFN]]) is typically 4 or 5, resulting in 1 / 4 / (0.26&nbsp;MHz) = 0.96 programmes/transmitter/MHz. This is 3.2 times as efficient as analog FM for local stations. For single frequency network (SFN) transmission, for example of national programmes, the channel re-use factor is 1, resulting in 1/1/0.25&nbsp;MHz = 3.85 programmes/transmitter/MHz, which is 12.7 times as efficient as FM for national and regional networks.

Note the above capacity improvement may not always be achieved at the L-band frequencies, since these are more sensitive to obstacles than the VHF band II frequencies, and may cause [[shadow fading]] for hilly terrain and for indoor communication. The number of transmitter sites or the transmission power required for full coverage of a country may be rather high at these frequencies, to avoid the system becoming noise limited rather than limited by co-channel interference.