The art of noise: high-definition sound explained

Fri, 4 Dec 2009, 1:30pm

Blu-ray offers more than just top pictures – it also delivers the best sound in home cinema, so you get to hear movies exactly the way Hollywood hears them



According to Randy Thom, one of Hollywood's greatest sound designers, "If you look closely at and listen to a dozen or so movies you consider to be great, you'll realise how important sound is in many if not most of them".

All the more reason to buy a Blu-ray player: it'll get you closer than ever to the technical prowess of the world's best sound designers. 

In fact, Dolby sales manager Andy Dowell asserts: "You get to hear exactly, bit-for-bit, what the mixing engineer heard in the studio."

Blu-ray does it better
Warren Mansfield, director of consumer technology at THX, is equally effusive: "Blu-ray offers consumers a bunch of advantages on the audio side: for example, it's the only way of getting discrete 7.1 audio right now. Also, the higher fidelity on offer gives listeners a wider dynamic range, and that's refreshing: it's a great step forward."

And Anthony Wilkins, director of marketing at DTS, puts it this way: "When we talked about data compression for DVD sound, what we really should have said was data 'reduction', because elements of the original source PCM audio are permanently discarded during the encoding process. With Blu-ray's new lossless audio codecs, that doesn't happen: the result is identical to the original."

Here's how it works: Hollywood's master-quality movie sounds are engineered as uncompressed 24-bit/48kHz PCM audio (better than CD quality, which is 16-bit/44.1kHz PCM) before being mixed in the studio on a massive mixing desk like the one shown below (used at California's famous Skywalker Sound).

After that, the final soundtrack is usually heavily compressed to create final versions of the movie for distribution on film or, subsequently, for domestic use. This is similar to the way MP3 works on a CD-quality piece of music: indeed, Dolby Digital, the most common system, stores audio at transfer rates very similar to a good MP3 (384 to 448kbps).

This compromise is enforced by the technical difficulties involved in cramming surround sound on to a film reel, a limited-capacity data disc or, most recently, on to a DVD. But Blu-ray has up to 50GB of storage capacity, so the notion of 'cramming' is a bit redundant.

In fact, there's so much storage space on a 50GB disc that it can even accommodate a 7.1 channel 24-bit/48kHz PCM soundtrack, if desired by the studio.

Lossless can help
It's possible to fit uncompressed PCM audio onto a 25GB (single-layer) Blu-ray disc too, but it takes up a relatively large proportion of the available space.

To create room for extras, soundtrack options and video, film studios have adopted two approaches. Some prefer to downconvert the 24-bit PCM original into a 16-bit/48kHz version. This still sounds very good, because even downconverted, uncompressed PCM will deliver more dynamic range and detail than Dolby Digital.

An alternative is to use a 'lossless' packaging system, either DTS-HD Master Audio or Dolby TrueHD. These work rather like zip files in home computing: they repackage the 24-bit/48kHz PCM master into less space, rather than downconverting it.

All that's required is some way of 'unzipping' the data file to recover the PCM audio: it can be done inside your Blu-ray player, or inside most new surround amplifiers.



The best quality ever
The result is that a 24-bit/48kHz PCM original soundtrack packaged using Dolby TrueHD lossless uses about half the disc space of uncompressed audio. In theory, it'll be bit-for-bit identical to the 24-bit/48kHz PCM studio master: that's certainly what Dolby and DTS assert.

Equally, these losslessly packaged 24-bit soundtracks should sound better than a downconverted 16-bit/48kHz PCM alternative.

Whatever the theory, the key point is that most Blu-ray film soundtracks are far more dynamic and spacious than DVD equivalents. And if you're thinking, 'That's fine, but I won't hear any difference on my set-up at home', you'd be wrong.

Even through a TV set, Blu-ray sounds crisper, while through a proper home cinema system, the sonic advantages are instant – you'll be hearing more of the real-deal Hollywood experience than ever.

More speakers on the way?
And Blu-ray's higher-quality sound has helped to spur further advances in surround sound technology, too. Dolby and Audyssey Laboratories, the company behind the automatic set-up and EQ systems used by a wide range of highly-respected AV amps, are now advancing the idea of home cinema using additional front 'height' speakers, able to develop a wider and more enveloping soundstage than with regular 5.1.

That means you could, if you felt sufficiently motivated, be listening to your movies through a 9.1 speaker system.  We can't imagine many UK households embracing that premise just yet - but who knows? With Blu-ray driving things, anything's  possible...

Those logos explained



9.1 SURROUND SOUND
This is a Dolby Pro-Logic IIz set-up: what do the other logos and badges on your AV amplifier mean?


Space-efficient: up to 6mbps quality


Lossless: gives up to 18mbps quality


Processing mode: Up to 9.1 channels

 

Processing mode: Found in some amps; supports 7.1 sound

 

Processing mode: As with Pro-Logic IIz, offers the option of height channels, but also 'width' channels

 

Offers up to 6mbps quality sound


Lossless: Can give up to 25mbps quality

 

Comments

Great article!

Really interesting article but something has puzzled me for some time. If blu-ray offers much better sound quality than DVD and CD why isn't the music industry offering albums in uncompressed form on audio only Blu-ray?

They are, Paul, but only small-scale at the moment: see www.2L.no,for example.

IMHO this is still not the perfect sound. Why is DSD not considered for movies yet?? Plenty of space on a Blu-ray!?

Cheers Andrew, it's pretty specialised stuff on 2L at present but it will be interesting to see what is released on BD in the future.

Nice article and information about Dolby Prologic IIz.

My only question would be regarding the other codecs - how can a straight comparison with bit rate and quality be made?  Conceptually most people would not hear the difference between a normal lossy DTS 1.5Mbps and the extended DTS HD codecs - all things being equal e.g. same master, sampling frequency and bit length (e.g. 16 bit).   The real advantage of the new codecs comes with the ability to have higher sampling frequencies and bit lengths (which in my opinion give better sound quality) and an increased number of channels.  Unfortunately I have only a handful of Blu-rays which take advantage of this. Sad  

Nice article - thanks.  Something which has been bothering me for a while is the appearance of films in 5.1 (albeit lossless) on Blu-ray, which were released in 6.1 (DTS-ES) on DVD - Gladiator and Fight Club are recent examples.  I'm continuing to run 5.1 lossless through Dolby PLIIx to create a 7.1 soundstage, but I wonder whether we're being short-changed by these 5.1 Blu releases.  Any thoughts?

blu-ray its really interesting to known about it.