In cinema terms sound can tell you where you are and who else is around you, even if you cannot see them. It surrounds us in a way that vision - even high definition vision - cannot.
Built-in speakers offer a fraction of what is available
And as such, those in the film industry believe it is crucial in helping us believe what we see.
"Along with HDTV the soundtrack was specifically made to give you six channels of digital sound," said Robert Heiblim of speaker systems development company Altec Lansing.
"The intent of the makers of these TVs, and indeed the entire system, is actually to give you the home experience of a movie theatre.
"When you don't turn on that soundtrack, or you don't maximise it, then you're literally not seeing the whole picture."
But what exactly is HD sound? According to the magazine What Hi-Fi which has been testing sound for a quarter of a century, HD sound does not exist.
"There is no standard for HD sound," explained editor Clare Newsome.
"A lot of people are starting to put it on products and there's a lot of potential for confusion out there."
While it is important to understand that manufacturers could slap the label HD on any half decent audio system the lack of a standard has not meant a lack of progress.
HD DVDs have the space for uncompressed sound
Many people have heard of Dolby Surround sound or DTS - they have been around for over a decade and could be described as hi-def.
But now everything has just got one step better. Unlike standard broadcasts most HDTV automatically includes surround sound, and there are now brand new sound formats for HD-DVD and Blu-Ray discs which, for the first time, have the space to carry uncompressed sound.
This delivers a perfect replica of the movie's soundtrack through a players' HDMI socket.
The HDMI cable typically would run from the player to the amp, which takes the audio and passes on the picture via another HDMI cable to the TV.
The amp decodes the sound signals and sends them to the surround sound speakers. The sound can also be channelled through six analogue phono outputs but this is a more messy solution as far as cables are concerned.
Listening to HD
Trouble is we do not yet have all the kit we need to experience it.
"From the summer we have got a lot of new kit coming out, a lot of it quite affordable, and a lot of it will include these new HD formats," said Ms Newsome.
"We've got the next generation of Dolby and DTS - Dolby True HD and DTS-HD or Master HD audio to give it its full name. From the names Master and True you're being told that it's uncompressed.
Chances are you have crushed the amount of data a CD would have given you by 90% just to get it onto a portable player
"You watch something like Casino Royale and it's just amazing, a whole extra level of cinematic. And the chances are that will sound better than you've heard in a small multiplex."
The good news is that you can experience some of the improved quality simply by hooking up an HDTV or player to your existing sound system.
Just do not rely on your TV speakers - HDTVs may offer the best in vision but the built-in speakers deliver a fraction of what is on offer because all HD broadcasts are now in surround sound by default.
And if you are thinking about a nice new set of wireless speakers be warned. Some will not cope with the new sound formats, so check first. In this case you will need to select a compressed sound format like standard DTS.
"With the change from CD Discmans to MP3 people haven't realised but they've lost a huge amount of audio quality," said Geraldine DeBonis of Creative. "By ripping a CD track to MP3 or WMA a lot of audio is lost."
Unless you have been ripping or copying your CDs in a lossless format chances are you have crushed the amount of data a CD would have given you by 90% just to get it onto a portable player.
Lossless compression is where a file is reduced in size, but where the algorithm used to do so also allows the exact original data to be reconstructed from the compressed file.
For the last two decades Creative has been aiming its market-leading Sound Blaster sound card to PC gamers and now it is targeting the film and TV lover trying to re-master low-grade audio on the fly.
"If you're looking at the before and after soundwaves you can see that in the MP3 version all of the changes in audio energy levels are actually dumbed down, curtailed," said Darragh O'Toole of Creative.
The growing capacity of hard drives, which are falling in price, means we can now afford to download or rip in better quality.
"We understand what has happened during the process. If you look at our after-phase you can see how we've restored these. So the strength and energy has been restored to things like the bass drums, you'll hear it come much more alive with crisp snare drums and nice, tight high-hats at the high end."
The system also enhances downloaded films with a "pseudo surround sound experience", even when presented with a mono soundtrack - throwing atmospherics and higher airier sounds to rear speakers while keeping the main action or dialogue in the front.
A new iPod dock offers the same features, which the company hopes will save us having to buy or re-copy our music and films collections all over again.
Audio is becoming big. Most Intel chipsets for example now have basic support for high-quality surround sound.
In March, EMI became the first record label to reissue its library at a higher quality bit rate.
And the growing capacity of hard drives, which are falling in price, means we can now afford to download or rip in better quality.
All these changes mean our digital sound is likely to stage a very unsung, overlooked and quiet revolution.