For many viewers with hearing problems, subtitles - and other associated services - can be vital in helping them get the full benefit of BBC programmes.
Gloria McGregor: Relies on subtitles
But the service isn't perfect, particularly on news programmes, as viewers often call in to point out. One of them, Gloria McGregor, came in to the BBC to find out how subtitles are provided and if the service can be improved.
I lost much of my hearing through illness many years ago and rely on the subtitles to help me follow television programmes. I also lipread, so being able to see the faces of speakers clearly is important.
But I often find when watching news and sport that mistakes in the subtitles can be very distracting.
Mistakes can be distracting
On one morning, errors included "curse cards" instead of coastguards and "verities" for penalties. By the time you've worked out what was actually intended, it's easy to lose the thread of the sentence.
I also find, on BBC News 24 in particular, that all the captions and graphics on the screen mean the subtitles are sometimes almost in the middle of the picture, where they can obscure the speakers' mouths - not very helpful for lipreaders like me!
So is there anything that can be done about this? On my visit to the BBC I first found out how the subtitles actually get on to air. There are two methods:
Stenography - the team of stenographers listen to the words and type them out on their special stenography machine, which has no markings like a normal keyboard, but produces a range of phonetic sounds.
- Respeaking - this is a moderately recent technique using voice recognition software. The words of the broadcast are repeated into a microphone, and they are reproduced on the TV screen.
Alannah Murray is one of the stenographers who mainly work in 15-minute stints transcribing news and sports programmes. It's quite intense work, so I'm not surprised most of their time is spent in short bursts.
Stenographers use a special phonetic keyboard
They prepare for news bulletins by accessing the computerised running order to see what stories are coming up.
They also have researchers to help with names and spellings likely to arise.
"The steno machine works a lot like a piano, in that a pianist will press several keys at once to get a certain sound," explained Alannah. "With our steno keyboard we press lots of keys at the same time to get a phonetic sound, so that's the reason we can write so fast.
"But we also have a series of shortforms. So for instance if I want to write the word 'environment', I could write that in one stroke. It's all so that we can write, faster, cleaner and more accurately."
Those shortforms are important in helping the stenographers keep up with the news presenters and reporters.
Alannah Murray: "We have to write at above 98% accuracy"
"A person who is speaking on the One or Six O'Clock News usually speaks at about 180 words a minute," Alannah told me.
"If you're doing a programme that Jeremy Paxman is hosting, like Newsnight, it can be around 220 words a minute.
"When they speak at speed it's very easy to miss one finger and for a word to become a different word altogether, which is one of the reasons it comes out inaccurately on screen.
"But we still write at above 98% accuracy - we can't go on air unless we achieve that accuracy rate."
The technique of respeaking is very different, but seems to me a skill that also takes some while to master.
Assistant producer Gary O'Key describes it as like a simultaneous interpretation but in the same language. As well as repeating the words, respeakers put in punctuation and also add colour changes, indicating that a different person has begun talking.
"There is only a finite speed you can go at so there are times we have to edit for speed," said Gary.
Respeaking is well suited to news programmes
"What we're aiming to do there is to get all the meaning across without changing it, so the subtitles might not always exactly match the spoken words.
"Most of the errors which come up will be what we call misrecognitions. Because speech recognition works on probability, it's not an exact science so it's nigh on impossible to get it 100% accurate.
"So the most common mistakes will be words which we've said but which haven't been correctly recognised by the software."
Gary told me respeaking was a good technique for live news and sport programmes.
Jokes and puns
"It's far less suited to something like a game show or a comedy or a chat show because people tend not to speak in such well constructed sentences," he explained.
"They sometimes make up words, there are jokes and puns and that kind of thing and it doesn't really lend itself to this type of technology."
It seems to me that respeaking may well be a more accurate system, even if the odd mistake will bear no relation to the word intended.
But there is a delay between the original words being spoken and the subtitles getting via the computer and back on screen. That makes it difficult for lipreaders, who really want speech and subtitles to be pretty much simultaneous.
It's not such an issue on pre-recorded programmes, where subtitles are added before broadcast. They are in synch with the spoken words and the subtitles are sensibly placed on the screen.
I met the head of business development at access services, Toby Blizard, and asked him if he thought the accuracy of live subtitling could be improved.
"I think the honest answer is that there will always be a certain level of inaccuracy because TV is that way - it's hard to get it perfect all of the time," he said. "But we are continuing to work hard to provide the highest level of accuracy we can."
How about the question of subtitles being so high up the screen they mask the speaker's mouth?
Sometimes subtitles obscure the speaker's mouth
"We're always working with the producers of the programme, as well as the people who produce the subtitles, to ensure they're positioned in a way that gives the maximum benefit to the viewers and also conveys the right meaning of the programmes," Toby told me.
"Sometimes they have to position them in certain places because that's what the programme demands. But they're very mindful that the audience needs lots of different cues to understand the programme content and they're doing what they can to make it as visually appealing and as accessible for you as they can.
"But sometimes it's not as easy as it seems to get them in the right place at the right time."
However, the BBC does seem committed to providing services like subtitling - there's also signing and audio description for the blind and partially sighted.
Toby Blizard: All programmes subtitled by 2008
"The BBC has said it will provide subtitles for 100% of it programmes by 2008," said Toby, "and at the same time it will provide 5% of signed output and 10% of programmes will be audio described."
Having seen the subtitlers in operation, it seems to me that there are bound to be some mistakes in live news and sport. Also the issue of where the subtitles appear on the screen is something that is quite difficult to resolve at the moment.
I will suggest to the lipreading classes I teach that there needs to be some level of compromise, and that they could treat any mistakes as lateral thinking exercises!
But I must say how impressed I was by both the organisation and the people involved in putting this important service on to our screens.