3.00 - 4.30pm, Saturday 24th December

HD sound logo.

On 24th December 2011 Radio 4 broadcast the annual Festival of Nine Lessons and Carols live from the chapel of King's College, Cambridge in HD Sound.


About HD Sound

What is HD Sound

HD sound means 'High Definition' sound.

Sound reaches our ears via analogue sound waves. However processing these sound waves electronically tends to distort their original shape. Digital processing is much less distorting. The conversion of an analogue signal to a digital signal is achieved by sampling the sound waves Currently we are using a sampling rate of 128 kb/s. The HD stream is being sampled at 320 kb/s, which results in better sound.

What is the best way of listening to A Festival of Nine Lessons and Carols HD?

If you listen on the small speakers built into a laptop you're unlikely to notice a big difference, but if your computer is connected to a good-quality sound system or high-quality headphones we think you'll appreciate the extra clarity and detail in the sound.

Can I hear other programmes in HD too?

We are offering A Festival of Nine Lessons and Carols live in HD sound as a one-off experiment. At present there are no plans to extend the service to other Radio 4 programmes. Radio 3 broadcasts live in HD sound all year round.

What do I do if it doesn't work?

This is an experiment so it may not work for everyone. If it doesn't work for you, return to the Festival of Nine Lessons and Carols home page and listen to the normal audio, accessed from the top right corner of the page.

Why do I occasionally lose the stream?

This live stream requires more bandwidth than the original stream. If your bandwidth drops because someone else is using your internet connection, the stream may falter and start to buffer. Buffering is an automatic process when the computer stores extra data (filling the buffer) before playing the audio. Having more audio data in the computer's memory than are actually needed at each precise moment compensates for momentary delays in transmission from the source. If the stream fails completely either go to the normal stream as above, or restart it from the Radio 4 in HD link.

Find out more about HD Sound experiments at the BBC

Listening to the Proms in Extra High Quality: Rupert Brun, Head of Technology for BBC Audio and Music, explains the thinking behind the experiment.

BBC Proms in Extra High Quality on the Internet- The Tech: Rupert Brun explains the technology behind the experiment.

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