By Geoff Adams-Spink
Age & disability correspondent, BBC News website
Thanks to government and Arts Council grants, more and more theatres in England are able to offer captioned performances to people with impaired hearing.
Captioning is an emerging craft that demands a combination of skills - not least the ability to maintain concentration for long periods.
In theory, captioning a live stage performance should be simplicity itself - all the lines are loaded into a computer so all you have to do is display them at the right time.
£1m is being spent to improve access to performances
If only it were that simple.
Roz Chalmers was one of the first people to train as a captioner and admits that in the early days, the whole process was a question of trial and error.
"We started off by making - not exactly mistakes - but assumptions that we later looked at and felt needed to be revised," she told the BBC News website.
These days, the company that provides captioning for theatres, Stagetext, has developed a recognised course and is now in the process of training new entrants to the profession which is still short of people.
Preparation is everything in the art of captioning, says Ms Chalmers.
"There is no better way of finding a mistake than seeing it in orange letters three inches high in the middle of a crowded auditorium."
Breaths and pauses
Captioners not only have to convey the dialogue on the three-line display, they also have to make decisions about whether or not to describe sound effects and other essential elements of the performance.
The first task is to attend a performance of the work and mark up the script, looking for breaths and pauses.
"You are actually marking your script to make sure you are following how the performer actually performs it," says Ms Chalmers.
It is also vital to make sure the script has not changed.
It then has to be formatted using specialist software and checked against a further two performances for inconsistencies.
After rehearsing "outputting" the text using a video of the performance, the captioner is then ready for the big night.
During the performance, the trick is to display the text at exactly the right speed.
Too early, and an actor's dramatic line will be pre-empted.
"If you put it up too late then the deaf audience is laughing after everyone else has finished," says Ms Chalmers.
Not all actors are word perfect, and the captioner has to be constantly on the lookout for lines that are skipped so that the words on the display match what is being said on stage.
Going on tour provides an additional layer of challenge because lines and even whole songs are sometimes changed for local audiences.
Pantomime can be even more demanding because there are often ad-libs to be conveyed.
Hours of preparation are needed before the show
"The software I use means that I can put in a variety of possibles and then jump to the right one on the night.
"Until I started working here, I didn't realise just how 'live' live theatre really is."
The alternative to the hours of preparation work would be to put up the text in real time - something which, according to Ms Chalmers, would not serve the audience well because they would be seeing the words a few seconds after they were spoken.
Heather Jackson became profoundly deaf in just a few days when, aged 35, a virus killed the nerve endings in both ears.
Now chairman of the National Association of Deafened People, she mainly uses lip-reading but she was unable to tell what was happening on stage and so stopped going to the theatre.
But seven years ago she attended a captioned performance at the Barbican in London and was delighted by the experience.
"Suddenly, there I was, back in the magical world of the theatre, able to follow everything that was said," she says.
"Thankfully, there's now a system in the UK that can provide access to the theatre for the large number of deaf people for whom loop systems and sign language interpretation is not an option."
Captioned performances are still few and far between. But, thanks to almost £1m in grants from the Arts Council and the Treasury, more performances in England will be made accessible to deaf audiences through the See a Voice project.
Over the next three years 60 venues will benefit from new equipment, and trained operators, in order to increase the number of captioned shows as well as performances that are "audio described".