While digital TV, both broadcast and IP-delivered, offers great potential for interactivity and receiver functionality, it is all too easy to overlook the needs of those affected by sensory and physical disabilities. Steps can be taken during programme-making and publication to ensure that content is accessible to the widest possible audience. Similarly, unless care is taken in the design of receiving devices , many potential users will find them difficult and complex to use.

The DTG Accessibility Working Group strives to make both services and products accessible and, to this end, produces guidelines for programme-makers and manufacturers alike

The World Health Organisation (WHO) states, in a 2013 Fact Sheet, that there are a billion people worldwide with some form of disability. It also confirms that the incidence of disability is increasing due to population ageing, amongst other causes.

According to the European Disability Forum (EDF), One in four Europeans has a family member with a disability, suggesting that around 25% of households in Europe include someone with a disability.

Both sight and hearing loss are widespread disabilities in the UK and Europe. At the same time, television is arguably the most prevalent medium used by people. Being able to use television programmes is not just nice to have, but indeed a key part of citizenship and participation. That is why the accessibility of television services is so important.

Using an audio-visual medium like digital television creates challenges for specific groups of disabled and older people. Individuals with sight or hearing loss are particularly affected, but there are also accessibility challenges for people with physical and cognitive disabilities.

Improving TV Accessibility

Vitruvian man icon representing access for allFrom early on, the DTG has recognised the needs of disabled television consumers and has been active in trying to harness opportunities to improve the accessibility of digital television.

DTG and its members contributed significantly to the Government's Digital Action Plan, including in the work to ensure that accessible solutions were available to older and disabled people as switchover was taking place in the UK. DTG has also published the U-Book, which complements the DTG D-Book and provides detailed Usability and Accessibility Guidelines for manufacturers.

More recently, the DTG's focus has been on Connected TV and ensuring that access services such as subtitles and audio description are as widely available as possible.

As television evolves, the DTG Accessibility Working Group continues to develop guidance, define opportunities to harness new technologies to improve services and products and raises awareness amongst key stakeholders about the need for accessible solutions and content.

The DTG's ground-breaking work on Text-to-Speech for digital television (see Text to Speech tab above), through a partnership with DigitalEurope, culminated in an International Standard IEC 62731: Text-to-speech for television - General requirements.

In addition to ongoing work to keep the U-Book up to date, the Accessibility Working Group is now also preparing guidelines on the clarity of broadcast speech.

Participation in the DTG Accessibility Working Group by interested parties is welcomed. The Working Group includes representatives of manufacturers, broadcasters, charities and organisations working for those with a wide range of disabilities, including sight and hearing loss.


Disability is defined in the UK Equality and Human Rights Act, on which more information can be found at:

Resources and Publications

The older DTG Implementation Guidelines and Recommendations for Text-to-Speech have been updated and are now included in the U-Book.

Meetings and Events

Details of DTG events can be found on the DTG Diary page

Other useful Links

User groups for Accessibility

Television viewers are individuals, each with their own preferences and abilities. Nevertheless, for practical reasons it may be helpful to identify some of the key stakeholder groups for the DTG's accessibility and usability work.

People with Hearing Loss

Possibly the largest single disability demographic are deaf and hard of hearing people. One in 6 people have a hearing loss, affecting more than 10 million people in the UK. These numbers are likely to increase as the population ages. Yet, despite the prevalence of hearing loss, it is also an often overlooked group and one that is very diverse in terms of its make-up and requirements. The most common cause of hearing loss is the ageing process.

Hearing loss is often categorised on the basis of degree of loss, from mild, moderate to severe and profound. People who develop hearing loss later in life usually have acquired spoken language, whereas those born deaf or with severe hearing loss from birth (or shortly thereafter) often use British Sign Language (BSL). BSL was recognised by the Government as a language in its own right in March 2003 Using the 2011 Census there are approximately 25,000 people in the UK aged three and over who use sign language as their main language. It is a visual language, with its own grammar and principles, which are completely different from the grammatical structure of English.

A significant number of hard of hearing people use hearing aids. There is also a (much smaller) group of people with cochlear implants in the UK.

A common problem for people with hearing loss is that people experience difficulty in discerning speech from background. Even the minor hearing loss that is a natural result of ageing leads to a noticeable reduction in the ability to follow dialogue over background sound. The DTG Accessibility Working Group is currently involved in a clean audio project to improve the audibility of speech in television programmes.

Subtitles are essential for many people with hearing loss, while Sign Language interpretation opens up content for those for whom Sign Language is their first language.

Blind and Partially Sighted People

Despite common misconceptions, blind and partially sighted people do use television, just like other consumers. In fact, many people with sight loss have some perception and most, of course, are able to enjoy the sound. Nevertheless, blind people and those with significant sight loss are arguably the group that faces the biggest accessibility challenges. They face significant barriers both in terms of using television products (interface accessibility) as well as with regard to content (where Audio Description is a key service for this group).

People with Colour Blindness

Colour blindness affects about 8% of men but only around 0.5% of women. In most cases colour blindness is genetically inherited, while diseases such as diabetes and medication are other common causes.

The most prevalent type of colour blindness is red/green colour blindness where all colours that have a red or green component are mixed up. Nevertheless, colour blindness can occur for the whole colour spectrum and even black can be confused for dark green or dark blue in some cases.

Like other conditions, colour blindness comes in varying degrees from mild over moderate to severe. Typically, most people with a moderate form of red/green colour blindness can only identify accurately 5 or so coloured pencils from a standard box of 24 pencil crayons.

People with Physical Disabilities

The term "physical disabilities" covers a quite wide ranging set of conditions and abilities. This user group includes people with motor impairments, dexterity barriers as well as wheelchair users and individuals with missing or differently formed limbs. There are also individuals who are partly or wholly paralysed.

For this group, interface accessibility (usually via alternative input devices) tends to be a high priority. Some can use traditional remotes, but many cannot. The use of specialised keyboards, large button remotes, single switch devices and voice control are amongst the tools used by this group.

People with Cognitive Disabilities

Just as for other groups, people with cognitive disabilities are a varied demographic. Indeed, there exist many types of cognitive disabilities covering a wide range of difficulties and deficits involving language understanding, reading, memory, visual comprehension, problem solving, reasoning and reduced mathematical comprehension.

Sometimes the origins are genetic, in other cases the result of injury, trauma or as a consequence of diseases such as meningitis or brain tumours.

Dyslexia is often included in the group of cognitive disabilities, being primarily a reading disability.

Older People

The most common cause for disability in the UK and Europe is the ageing process. Sight and hearing loss, reduced dexterity and sometimes decreased cognitive faculties are all typical corollaries of getting older. While the degree of disability in older people is generally milder compared to other groups of disabled people, it is compounded by the fact that several of these conditions, both physical and sensory, tend to co-exist amongst these consumers rather than a single disability dominating the individual's profile of abilities and preferences.

Resources and Publications

The older DTG Implementation Guidelines and Recommendations for Text-to-Speech have been updated and are now included in the U-Book.

Meetings and Events

Details of DTG events can be found on the DTG Diary page

Other useful Links

The DTG U-Book

The DTG Accessibility Working Group maintains the U-Book, the UK Digital TV Usability and Accessibility Guidelines, including Text to Speech.

The U-Book contains three parts:

  • Part A - Usability Guidelines: information on the best industry practices for ensuring a good, usable customer experience when using digital television products. This part includes guidance on remote controls, Electronic Programme Guides, User Interfaces, labelling, user documentation, etc.
  • Part B - Accessibility Guidelines: offers guidelines to manufacturers wishing to incorporate accessibility features into their products. This includes audio description, subtitles and text-to-speech features.
  • Part C - Connected TV Implementation Guidelines: these are currently under development by the Working Group and expected to be published later this year.

The U-Book complements the D-Book. In addition, the DTG Receiver Recommendations give details of the mandatory requirements for accessibility features in receivers.

The challenges that disabled and older people face when using television can be divided between interface accessibility barriers and impediments in using the television content itself. The U-Book provides guidance on both these areas.

Also, as more and more features are added to television products and services, some viewers find them more complicated to use. The advent of Connected TV brings many benefits to viewers, bringing together traditional television services with Internet based content.

Connected TV gives consumers more choice and more interactivity. However, the added functionality and jargon of Connected TV can create new challenges for accessibility and usability. The Connected TV chapter in the U-Book helps manufacturers in addressing those barriers. Connected TV also offers new prospects for improved accessibility beyond what could be done with traditional solutions. The U-Book's Connected TV section identifies these opportunities to harness Connected TV as a means to bring innovation to accessibility-related features and content.

Resources and Publications

The older DTG Implementation Guidelines and Recommendations for Text-to-Speech have been updated and are now included in the U-Book.

Meetings and Events

Details of DTG events can be found on the DTG Diary page

Other useful Links

Text-to-speech in Television

Blind and partially sighted people face significant barriers in using television products. Where content is concerned, the DTG and the UK have been pioneers in the provision of audio description, a major feature to give this user group an equivalent experience in consuming television programmes.

However, in addition to content accessibility, the television product itself, its User Interface (UI), also needs to be accessible to people with sight loss. A talking interface can provide a substantial improvement in accessibility and usability for this group of consumers.

Such talking features provide a spoken alternative to the visual menus and other components of the default interface. By using text-to-speech in a television solution, a person operating the product via the spoken interface will receive the same feedback and be able to perform the same tasks as someone using the default (visual) interface.

The Digital TV Group, working with organisations representing blind and partially-sighted users, has been a pioneer in this field. It started work on text-to-speech in 2007, bringing together industry and other stakeholders to write a technical specification for Text to Speech (this has since been included in the U-Book). This initial specification was referred to in the UK Government's Usability Action Plan.

Later, this excellent piece of work by DTG was adopted by DigitalEurope and taken to the International Electrotechnical Commission (IEC). This led to the IEC setting up a project group and creating International Standard IEC 62731:2013: Text-to-speech for television - General requirements.

As a result of this work, we have seen more and more solutions with integrated text-to-speech (talking features) being introduced to the UK market.

Resources and Publications

The older DTG Implementation Guidelines and Recommendations for Text-to-Speech have been updated and are now included in the U-Book.

Meetings and Events

Details of DTG events can be found on the DTG Diary page

Other useful Links

Access Services

In order to make television content accessible to people with sensory disabilities and to older viewers, the UK has been a forerunner in the delivery of subtitling, signing or audio description. Some 70 television channels in the UK now provide access services.

The DTG D-Book describes the technical means for delivery of access services. The U-Book contains best practice guidance surrounding the implementation of access services in digital television solutions.

Audio description and subtitles are closed services, which means the viewer can turn them on or off as they require. Sign language content in the UK is delivered as an open service, i.e. whereby the signing is part of the main video track and cannot be turned on or off. Prototype systems demonstrating closed signing have been developed, but there are many technical and economic barriers to their real-world deployment.


Subtitles are an elective service which, when turned on, provides a text representation of the dialogue or commentary. They are normally shown at the bottom of the picture and benefit from the use of different-coloured characters for different speakers, when applicable. Subtitles are the most used access service in the UK, with millions of viewers enjoying them. Amongst the main user groups for subtitles are those with hearing loss, older people and those for whom English is not their first language. Problem areas with subtitles include the accuracy of live subtitles and timing.

Another issue is the availability of subtitles on non-domestic TV receivers such as are found in many hotels and fed from an in-house distribution system. A useful note [1] on this has been issued by Action on Hearing Loss and the topic is being pursued by the DTG Accessibility Group.

Use of Assistive Listening Devices

Whilst subtitling is the obvious facility to assist the hard-of-hearing in accessing TV programmes, for many viewers with moderate hearing loss subtitles are intrusive in a family-viewing environment and unnecessary if the TV audio can be made available to them at a higher level than for normal viewing or in a processed form that emphasises the higher frequencies. Whilst many receivers have an option for the audio to be processed to give an output that is more intelligible for the hard-of-hearing, this is suitable only for solitary viewing.

One solution is the use of assistive listening devices (ALD). In its simplest form this consists of a variable-gain amplifier connected to the TV receiver and feeding a listener's headphones. More complex devices allow the listener to be free of the wired connection to the TV receiver through the use of wireless or infrared connection to the headphones or to an induction loop in the home.

All these solutions require connection to the TV audio. Historically this has been achieved through the use of a receiver's SCART adaptor or RCA phono sockets without muting the TV loudspeaker and this is particularly important for mixed hearing / hard of hearing households Increasingly, however, receivers are equipped with only HDMI or optical connections to external devices such as soundbars or an ALD, but use of the connection disables the main speakers. Similarly, where a headphone socket has been provided, insertion of a plug usually has the effect of muting the main audio output thus depriving the other viewers of audio through the receiver's loudspeakers.

The provision of facilities for enabling both the main and any secondary audio outputs simultaneously is strongly encouraged.

Audio Description

Audio Description is an additional narrative that describes the visual elements of a programme, such as the scene, actions, body language and expressions and is intended to make the programme clear through sound. Audio Description is used primarily by blind and partially sighted people and supplements the dialogue spoken by the cast.

There are two forms of Audio Description in the UK:

  • Broadcast-mix: this comes as alternative audio including both the standard programme audio and the audio description track, brought together by the broadcaster. When activating broadcast-mix audio description, the receiver selects this alternative instead of the default audio.
  • Receiver-mix: this is where the audio description is an additional audio track that the receiver combines with the main audio.

Sign Language

According to the 2011 Census, there are approximately 25,000 people who use British Sign Language (BSL) as their first language. There are many other deaf people who use BSL in addition to English. BSL is visual and a language in its own right; it is very different to English. To provide BSL interpretation for a television programme, a sign language interpreter is shown in-vision.


Resources and Publications

The older DTG Implementation Guidelines and Recommendations for Text-to-Speech have been updated and are now included in the U-Book.

Meetings and Events

Details of DTG events can be found on the DTG Diary page

Other useful Links

Clear speech

Complaints from viewers about the difficulty of understanding dialogue ranks high on the list of calls to broadcasters. Whilst the majority of those complaining suffer from some degree of hearing loss, this is not the only reason for the complaint.

In 2010 BBC Vision carried out two separate surveys with its Pulse on-line panel of 20,000 viewers to identify the issues which caused problems with television sound. The research showed that nearly 60% of viewers had some trouble hearing what was said in TV programmes. [BBC]

The research identified four key factors that can make it hard for viewers to hear what is being said:

  • Clarity of speech: poor and very fast delivery, mumbling and muffled dialogue, turning away from camera, people talking over each other, trailing off at the end of sentences.
  • Unfamiliar or strong accents: Audiences find accents other than their own harder to understand.
  • Background noise - locations with heavy traffic, babbling streams, farmyard animals, in fact any intrusive background noise can make it difficult to hear what's being said.
  • Background music - particularly heavily percussive music or music with spikes that cut across dialogue.

A common problem for people with hearing loss is that they experience difficulty in discerning speech from background sounds. Even the minor hearing loss that is a natural result of ageing leads to a noticeable reduction in the ability to follow dialogue over background sound.

More than 10 million people in the UK have hearing loss—about one in six of the population. This includes over six million people who could benefit from hearing aids (hearing loss of at least 35dB in the better ear). There are also 800,000 people in the UK who have severe or profound levels of deafness.

Effect of age on hearing

Age-related damage to the cochlea, or presbycusis, is the single biggest cause of hearing loss. This process occurs naturally as part of the ageing process. Other causes and triggers of hearing loss include:

  • regular and prolonged exposure to loud sounds
  • ototoxic drugs that harm the cochlea and/or hearing nerve
  • some infectious diseases, including rubella
  • complications at birth
  • injury to the head
  • benign tumours on the auditory nerve
  • genetic predisposition: at least half of all childhood deafness is inherited and so far scientists have identified 80 genes that relate to deafness. [AoHL]

The last official census put the UK's population at approximately 60million.

The Medical Research Council estimates that 9 million people in the UK (over the age of 16), have a hearing problem:

  • 0.7m are profoundly deaf or severely hard of hearing
  • 8.3m suffer mild/moderate deafness

Most of the 9 million deaf and hard of hearing people have developed a hearing loss as they get older. (Only about 2% of young adults are affected—at present: the fastest rate of increase among adults is now in the 16-24 age group.) Around the age of 50 the proportion of people with a hearing loss begins to rise sharply, and 55% of those over 60 are deaf or hard of hearing.

  • 1 in 3 UK citizens is 50 or over.
  • By 2020 it is estimated that half the population of Europe will be over 50.

The curves below illustrate the way in which hearing loss increases with age, both basic sensitivity and frequency-dependent loss.

Charts showing hearing loss getting more severe with increased age From Modern Sound Reproduction by Harry F. Olson, showing the average hearing loss-vs-age for men and women at frequencies from 250 Hz to 8000 Hz

A vital factor is that a majority of consonants, which are crucial to understanding, are centred in the higher frequency range, where hearing loss is most marked.

The following chart shows the expected increase in the UK population by 2033. Note the significant increase in the population aged 65 and over. So the number of people in the audience with limited hearing is increasing each year.

Projected increase in UK population between 2008 and 2033 is concentrated in older age groups

While subtitles are a solution for some viewers, many of those suffering from mild hearing loss prefer not to use subtitles, particularly for news programmes, as the delay and errors can be distracting. Consequently, even for this group, the clarity of speech is important.

A study carried out by the BBC in 2003 revealed that the over-55s account for nearly 40% of peak-time audiences, and that the average time spent watching all channels was, at 4hrs 21mins, about 45 minutes longer for the 55 – 65 year-old than for the population as a whole.

In 2010, the organisation Voice of the Listener and Viewer (, BBC and RNID (now Action on Hearing Loss) carried out a survey into the experiences of a sample of viewers of mixed ages and hearing abilities. Some of the results are presented below.

Self-assessed quality of hearing % of viewing for which difficulty experienced hearing the spoken word
Very good 2
Good 3
Moderately good 12
Poor 18
Very poor 27

Considering just the over-65s, 29% of programmes posed speech audibility problems to at least 10% of their viewers. The table below shows the results for different age bands, using selected programme material, showing that the over-65 age group have difficulties with four times as many programmes as the youngest group.

Age range % of UK adult population (approx) % having difficulty hearing speech in selected programmes
16-49 40 13
50-64 30 23
65 and over 20 53

The causes of these difficulties are varied, as seen below.

Reasons for difficulty
19% Foreign accents and dialects
13% Background noise
11% Background music (a particular issue for the elderly)
14% Mumbling and poor diction
11% Talking too fast

Background noise and background music account for a quarter of the difficulties. But most of the difficulties could be reduced, if not eliminated, by care taken in the programme-making process.

You can hear for yourself what it's like to have impaired hearing by using software simulators. Several are available, two of which are:

University College London's HearLoss - an interactive Windows PC program for demonstrating to normally hearing people the effects of hearing loss. With HearLoss you can replay speech, music and noise under a variety of loudness, filtering and masking conditions typical of hearing impairments. Best of all you can interactively change the settings and demonstrate their consequences.

University of Cambridge Inclusive Design Kit - demonstrates some of the main effects of common types of hearing loss in the UK. It gives an indication of how sounds might be perceived by affected people, at varying levels of severity. Its purpose is to help content creators to better empathise with those with reduced hearing capability, and to help them understand how capability loss affects the ability to interact with products, services and everyday life.

What can be done?

Many of the difficulties affecting the clarity of speech can be reduced or removed by care taken in the production process, including pre-production planning and quality control. Programme commissioners and producers have a role to play in ensuring that purchased and in-house programmes are made in a way that ensures clarity of speech and that this is not lost in post-production.

Whenever possible, prior to release a programme should be played through domestic quality loudspeakers to someone not involved in the post production so that any instances of unclear dialogue can be identified and rectified prior to transmission. Use of a hearing-loss simulator provides a convenient way of checking the clarity of the speech element of a programme and is encouraged.

Practical advice

The BBC's College of Production has made a number of useful training videos giving practical advice on, among many other things, acquiring, recording and post-producing sound for television. The following are relevant to clear speech and are freely available.

Pre-production planning

Content acquisition


Further reading

  1. Sound Advice, Richard Bates, ITV
  2. Digital Production Partnership technical standards – quality control

Resources and Publications

The older DTG Implementation Guidelines and Recommendations for Text-to-Speech have been updated and are now included in the U-Book.

Meetings and Events

Details of DTG events can be found on the DTG Diary page

Other useful Links