Since people started watching movies at home, there has been a drive to improve the sound quality. In a cinema, the sound comes from all around the room and produces a deeply involving experience. Home video players started off in mono, stereo was added later, and after that the clever people at Dolby worked out a way to create a surround-sound movie experience using just a regular stereo soundtrack. This system was called Dolby Pro Logic -- it used an external decoder that reconstructed surround sound from plain old stereo sound.

Pro Logic was the first generation, and is, by modern standards, pretty crude. You only get a mono rear-effects channel, a centre channel for dialogue, and the regular left and right stereo speakers. Despite its crudeness it's surprisingly effective, and the centre channel alone makes it worth the trouble.

When DVD hit the market, everyone marvelled at the picture quality, but in many ways that wasn't the most amazing part. DVDs contain full 5.1 surround sound, which gave full stereo rear effects, as well as dedicated centre, left and right channels, and a channel for bass known as LFE, or 'low frequency effects'. This channel doesn't contain much information, so only requires a small amount of data, and is the .1 in the 5.1.

With all these fantastic advances in surround sound, what can Dolby TrueHD possibly offer? Well, the idea of TrueHD is that it's uncompressed audio, and it's common knowledge that if you don't compress things, they sound a lot better.

So, do you need a new bunch of kit to make the most of it? Well, not really. Because the sound is recorded on the disc uncompressed, it should automatically sound a lot better on the same hardware as before. If you have a player with analogue audio outputs, you'll find hooking these up to a 5.1 amp will yield a massive jump in quality.

In order to pass Dolby TrueHD and DTS Master Audio over HDMI, you need to have a player and an AV receiver that can cope with HDMI 1.3, because only this latest HDMI standard has the necessary bandwidth to send uncompressed audio and high-definition video at the same time.