What is HD sound?

High definition sound offers multiple channels of digital surround sound, and higher quality surround sound

We like to refer to the new sound possibilities provided by modern home entertainment technology as high definition sound. We think of it as the equivalent of high definition video. Just as this can provide five times as much picture information as standard definition video, so high definition sound can provide a lot more audio detail and involvement to soundtracks.

It does this in two different ways, by providing:

1. More channels of digital sound
2. Better quality digital sound

More channels

Sometimes we like to pull out our Deep Purple CD ‘Machine Head’, and transport ourselves back to the uncomplicated early-1970s. But we also have the DVD-Audio version of this. Both versions provide the best that their respective technologies have to offer, and both are limited by the quality of the sound recording technology of the early 1970s.

Despite that limitation, the DVD-Audio version is much more enjoyable, mostly because it is easier to hear everything that is going on in the music. That’s because DVD-Audio offers 5.1 channel digital surround sound instead of the two channels of digital sound provided on the CD. This allows all the instruments to be pulled apart and delivered into our room without being mashed together in a confusing way.

And so it is with movies and even some TV shows. Where full 5.1 channel digital surround sound is provided, the clarity is improved enormously. It is far easier to comprehend the dialogue if it is being delivered from the centre speaker while the music swells from the other speakers, than when all the sound is mixed together into just two speakers.

For movies, that 5.1 channel experience ‘envelopes’ you into the sound. It is absolutely wonderful to be embedded into the movie by the swirl of sound behind and beside you as you’re watching Cars or The Terminator. Many moviemakers these days use surround sound as part of their narrative devices, surprising you with sounds from behind. Do not deprive yourself!

Better sound

High definition sound is, in addition to the extra channels, more accurate. More truthful.

That’s because new technology has allowed some of the older compromises to be eliminated. The old Dolby Surround from the 1970s was quite restricted in sound quality, but the Dolby Digital 5.1 available on some HDTV shows delivers excellent quality all around. Blu-ray steps things up even more, providing super-high resolution sound formats such as Dolby TrueHD and DTS-HD Master Audio.

These are sound delivery systems without compromise. They preserve the full integrity of the original sound in a way that standard Dolby Digital can’t, and can deliver up to 7.1 channels of audio. Some soundtracks employing these high resolution sound formats also offer 24-bit rather than the standard 16-bit sound, or 96kHz sampling rather than the standard 48kHz. The benefits of these improvements are rather technical, but we can assure you that each increase allows the original sound to be even more precisely – truthfully – replicated.

The source of the sound

High definition sound is proliferating, we’re happy to say. As we’ve suggested, not all HD sound is the same, but at a minimum Dolby Digital 5.1 meets our specification. This is becoming increasingly common on TV shows and movies broadcast on Australian HDTV channels, but it can also be enjoyed on standard definition TV (SDTV) channels. For example, the ABC recently broadcast a performance of Tchaikovsky’s ballet Swan Lake on its SDTV station using Dolby Digital 5.1 sound.

We expect Dolby Digital 5.1 to come to dominate free-to-air TV broadcasting over the next few years. Also expect from May 2009 the roll-out of digital radio (formally known as DAB, or Digital Audio Broadcasting). The standards for this are still under consideration as we write, but we expect these to be stereo (ie. two channel).

As for right now, in addition to some HDTV broadcasts, high definition sound is available on most DVDs, most modern console games, and with even better-quality sound on Blu-ray. Some equipment also supports DVD-Audio and SACD, two audio-only formats that failed to really take off but which, nevertheless, provide glorious high definition surround sound.

Reasons for high definition sound

1. Many modern movies gain their atmosphere from surround sound
2. Scary movies and thrillers like to have sounds sneak up behind you
3. Movie dialogue becomes clearer
4. Surround sound involves you in the onscreen action
5. High resolution surround sound is even better… it’s just like being there!

GadgetGuy tip – check your setup menu

Check the setup menus of your HDTV receiver. To get full Dolby Digital 5.1 sound, you will need to make sure that it does not convert the sound to ‘PCM’, which is usually a mere two-channel format. Instead, find out where the sound output is determined and set it to ‘pass through’ or Dolby Digital (the label varies depending on the unit).