High definition sound mates with HD pictures on Blu-ray, but just what does this mean? Thomas Bartlett explains.

High definition sound is what you get in the very best cinemas in the world, but you can also get it in your home. And it is vital if you are going to receive the full high definition experience. High definition video without high definition sound is like putting a V12 engine into a Model T Ford. It gives you only part of the high-speed experience, because you will still have to putter around corners. But add a Ferrari chassis to the V12 engine and you get the whole thing.

You should aim to match the quality of your high definition flat panel TV or projector to your high definition sound system. But when you take the plunge and start visiting stores to select your new high definition sound system, you will be bowled over. Not just by the sound quality of the various options, but by the terms used on the brochures and thrown about by the salespeople.

So let us equip you with an understanding of what all these mean and, in the process, what you absolutely have to know if you want to experience high definition surround sound in your own home.

What is high definition sound?

High definition (HD) sound has two distinct characteristics: it is true surround sound, and it is high resolution sound.

True surround sound means that the different parts of the sound that create the experience each have their own discrete ‘channel’. This means that each channel in a soundtrack carries discrete – or separate – sound information and employs separate speakers to reproduce it.

There are three speakers across the front of the room: left, centre and right. And there are two (or more) speakers across the back: surround left and surround right (and, optionally, one or two surround centres). Plus a subwoofer, which is fed by what is called the ‘LFE’, or Low Frequency Effects, channel. It is this that produces the thud of an explosion, the throb of King Kong’s footsteps.

High definition sound comes in many different forms. At a minimum it means Dolby Digital 5.1, or DTS 5.1. Both of these come from the early ’90s, when there was not much space to store the sound. So some of the fine detail was thrown away to allow all the channels to squeeze in. Still, they both deliver magnificent performance, and you will find them on DVDs and some HDTV shows.

High resolution sound

Dolby Digital 5.1 and DTS 5.1 are only the start of the story. There are also newer surround systems designed to take advantage of the greater storage space of new high definition DVDs, and to deliver what is usually described as ‘High Resolution’ sound.

High resolution sound is ‘better than CD’ sound, with the original sound recorded far more accurately than is possible with CDs. Unlike regular Dolby Digital and DTS, no fine detail has to be eliminated because there is plenty of space on the discs.

The oldest of these are those found on DVD-Audio and Super Audio CD. As their names suggest, these are both music formats, and both deliver absolutely glorious high resolution surround sound. We will not talk much about them, though, because they never really became widely available, and the range of discs is few.

Fortunately the new high definition video disc format, Blu-ray, has several varieties of high definition sound available. The soundtracks on these new discs can be in regular Dolby Digital or DTS. But many are also in the new Dolby Digital Plus and DTS-HD High Resolution Audio. While not full high resolution sound, these use much more space to store the sound, so it is usually indistinguishable from real life!

Even better are DTS-HD Master Audio and Dolby TrueHD. These are ‘lossless’ high resolution sound systems that keep the original sound intact so that it is delivered perfectly in your home. They offer three times the resolution of CDs, but with full surround sound of up to 7.1 channels.