Bewitched, bothered and bewildered? David Price cuts through the techbabble and tells the story of multi-channel audio, and details the latest 'high resolution' surround sound formats.

The words 'home cinema' still send shivers down the spines of many self-respecting audiophiles. After all, big black boxes packed to the gunwales with digital signal processing trickery, serious graphic equalisers and just about every flavour-of-the-month gimmick are hardly the stuff of dyed-in-the-grain audiophile systems, are they? True enough, but don't use this as a reason to dismiss multi-channel audio out of hand. 

Stereo, lest we forget, is just one particular take on the problem of recreating a recorded acoustic in the home. Ever since a squeak came out of the very first loudspeaker, audio engineers have been scratching their heads over this, and have come up with a variety of solutions.

Of course, the film industry has driven most of the development of multi-channel - as far back as the 1940s, Walt Disney used 'Fantasound' surround sound technology to heighten the experience of his animations - but don't let that put you off. Creating a believable acoustic is just as important in the home!

BACK TO BASICS - THE EARLY DAYS OF ANALOGUE MULTI-CHANNEL

MONO
Hard as it is to imagine today, mono is what most audiophiles used until the sixties, and it was capable of incredible musicality when 'done properly'. Monophonic sound is single-channel, unidirectional reproduction using one amplifier and speaker combination. 

It has an abiding virtue - wherever you are in the listening room, you hear everything identically (room acoustics notwithstanding, obviously). Everything appears from a single 'point' in space and - fascinatingly - even if you use two mono channels, the sound still seems to come from a point equidistant between the two speakers, creating a 'phantom' channel. 

STEREO
This was experimented with in various forms for many years before it made it into the home in 1958. Bell Laboratories' system used three channels, whereas the film industry used between four and as many as seven channels in early cinema installations. Two channel stereo in the home came about simply because it was all that LP records could realistically cope with. 

Then two channel stereo FM broadcasting arrived, further popularising the format and entrenching the idea that 'two channel' was 'stereo'. Now an entire generation of audiophiles has accepted it as the norm, although in truth it's just as arbitrary a way of recreating music as mono or multi-channel. 

Generally it offers a much more open sound than mono with a real sense of a 'sound stage'. Still, the experience very much depends on the mix. For example, when a symphony orchestra is recorded then even a simple pair of crossed cardoid microphones will capture the space and proportion of the sound. 

However, studio recordings often follow a convention where, along with various instruments panned left and right, strong monophonic elements are included to give more substance. By mixing, say, vocals to both left and right channels, the singer seems to be in the centre 'phantom' channel. 

Done well, it can be extremely convincing, but still has its limitations. Earlier stereo mixes were pretty bad - as many Beatles aficionados will attest - giving an extremely unnatural sound due to insufficient 'phantom' centre channel content.

QUADRAPHONIC
As technology progressed and prices fell, various early nineteen seventies manufacturers began to think there was a market for multi-channel. Thus was born the ill-fated quadraphonic system, which required two extra speakers in the rear corners of the listening room to reproduce specially 
encoded program sources. 

Several variants were produced, most of which were based on 'matrixing' techniques which folded the rear channels into the front channels by recording them with different relative phase, although there was also a 'Discrete' system that used four separate channels. 

Quad - as it was known - effectively carried four channels of information within a two channel recording, and could be read by a normal phono stylus and passed through to a receiver or amplifier with a quadraphonic decoder.

Although it was never called 'surround sound', and shared nothing in common with the cinema systems, quadraphonic could be justifiably regarded as the forerunner of modern Dolby Surround technologies. 

Sadly though, the world wasn't ready for it - thanks to turntable pick up cartridge (and record pressing) technology, Discrete quadraphonic wasn't practical, and the less adventurous matrixed systems proved a flop due to the high investment required. To cap it all. the systems proved largely incompatible with one another!

DOLBY SURROUND/ PRO LOGIC
Modern surround sound got its first breath of life in mid seventies cinemas with films such as Star Wars, Tommy, and Close Encounters of the Third Kind. A new format designed expressly for 35mm film prints, Dolby Surround used two tracks squeezed into the same space on the print occupied by the traditional mono soundtrack, made possible by the use of Dolby A noise reduction.

Of course, two channels weren't enough for cinema use (due to the wide gap between the left and right of the screen), but it was impossible to cram more than this on to the print, due to excessive noise. The answer was to use matrixing techniques developed for quadraphonic home stereo, where a centre and surround channel were 'extracted' from the two channel mix using clever signal processing. 

Dolby Surround fast became the standard for cinemas all around the world and the advent of stereo video machines in 1978, and then Laser Disc in 1980 (extremely popular in Japan, much less so in Europe) added impetus to the surround project. The arrival of the 'music video' also ushered things along - for the first time people were using their TVs for the enjoyment of music. 

In 1987, domestic Dolby Pro Logic decoders arrived, making it possible to decode front left, front right, centre and rear channels (often via two speakers) from a standard two-channel stereo source. The main sounds came from the left and right channels, the vocal or dialogue emanating from the centre phantom channel, and the ambience or effects information coming from behind the listener.

Thanks to its limited bandwidth (the surround channel only went from 100-7,000Hz), Dolby Pro Logic wasn't much cop with music but was surprisingly effective with film soundtracks, able to convey the sensation of sounds moving from front to rear and left to right. This said, it has been used for music-only applications - record companies including Delos, RCA Victor, BMG Classics and Concord Jazz have all produced Dolby Surround-encoded audio releases, with little success.

FUTURE PERFECT - THE INEXORABLE RISE OF DIGITAL SURROUND: DOLBY DIGITAL
Dolby's much vaunted digital format arrived in cinemas in 1992. While the 35mm film prints used in cinemas retained analogue Dolby Stereo soundtracks for backwards compatibility, an additional new digital optical track was placed between the sprocket holes. 

This permitted the famous 5.1 configuration that has became the industry standard. Front left and right, rear left and right, centre and LFE (low frequency effects) channels are provided, all offering the same quality. However, because the LFE channel only takes around one tenth of the bandwidth, it's known as 'point one'. 

Dolby digital offers a range of special features, such as downmixing from multi-channel discs for stereo listening or Dolby Surround decoding. It can provide dynamic compression to increase the level of quiet passages (making late night viewing/listening a reality) and even route low bass only to speakers capable of reproducing it.

This is all made possible by clever data reduction techniques, using perceptual coding to shave the digital datastream down to one twelfth of its original size. While the format's theoretical maximum bitrate is 640kbps, DVD discs allow only 448kbps in two channel and 384kbps in 5.1 modes. 

Dolby Labs argues that this, "provides sound quality that critical listening tests have consistently confirmed as on a par with original master tapes". Joseph Hull, Dolby Laboratories' Marketing Communications Manager, calls Dolby Digital, "the final link between the multichannel producer and home listener". 

DTS 5.1 SURROUND SOUND
While Dolby Digital fast became de rigeur on the home and cinema surround scene, a renegade format arrived with the appearance of Stephen Spielberg's Jurassic Park in 1993. The famous Hollywood producer took the view that Dolby Digital simply didn't sound good enough for his purposes, and turned to Digital Theater Systems for the answer. 

There are two key differences: First, running bitrates of 1.5mbps, DTS runs at a compression ratio of just 1:3, which is dramatically lower than Dolby Digital. As any MP3 user will know, this has obvious sound quality benefits. The second advantage is the sound of the actual codec itself - even running at identical bitrates, most believe that DTS sounds superior. 

DTS is an interesting point at which movie-driven surround sound crosses back into audio with real benefits. And much of the industry agrees - Pioneer's John Bamford says, "there's something very nice about this codec, everybody goes for it every time". So while DTS is a 5.1 surround system just like Dolby Digital, thanks to its better sonics, it has found itself being used for pure audio purposes too.

Indeed a range of DTS High Definition discs has sprung up, which because they're actually CD discs but not encoded in the Red Book format, can be played on most standard CD players if you take the digital output to a DTS-equipped processor or preamp. As almost all DVD (and DVD-A) machines have built in DTS decoding, these should play DTS HD discs without an additional processor.

Right now, you can get DVD video discs encoded with both DTS and Dolby Digital soundtracks. Curiously, the format used doesn't depend on the title as much as the region it's destined for. Many Region 2 PAL (i.e. European spec) discs come with Dolby Digital soundtracks, whereas a surprising amount of new Region 1 NTSC releases  (i.e. from the US) come with DTS sound. This is why multi-region compatibility is such an important issue for movie buffs and audiophiles alike - the former love the early movie release dates, the latter lust after the superior DTS coding used!

Title: 461 Ocean Boulevard. Artist:  Eric Claption. Formats: DTS (20bit, 5.1) Catalogue  HDS-4419

Confusingly, there are three 'types' of DTS discs around right now. First are the aforementioned DVD video discs with DTS 5.1 sound, second are discs on the DTS Entertainment label (mostly DVD-A with DTS mixes) and third are discs from DTS's High Definition Surround series such as this. 

These play in most DVD machines and all CD players connected to an offboard DTS decoder via the digital output. Confused - don't blame you! This disc falls into the latter category - mastering was done by Suha Gur with a Prism AD-1 analogue to digital converter, with monitoring courtesy of a Krell KPS-20 CD player and Millennium 2.4..6 DTS decoder/preamp.
 
Clapton addicts will know it's a 'seminal' album of course, and while the CD reissue may not have been enough to coax them to part with cash, this may well. If you have a decent DTS decoder (whether in your DVD player or AV preamp or processor) you'll be extremely impressed with the sonics. Frankly, the original recording isn't particularly special (the original vinyl first pressing isn't anything to write home about), but this DTS disc seems to get to the bottom of it in a way no silver disc has ever done before. 
 
It's very sweet and smooth, adding a lot of extra timbral and textural detail which the CD simply loses. The surround mix is faultless - nothing too way out, it simply adds subtle strands of ambient information to make you feel like you're in a concert hall. Two channel stereo sounds quite flat by comparison. It's actually very sweet and beguiling - almost as impressive as some more celebrated DVD-A pressings, in fact. By comparison, the original vinyl adds a touch more emotion and a little warmth and space, but I could happily listen to either through any system.
 

DVD-AUDIO
Although this new format has been much celebrated by the world's hi-fi press for 'pushing the envelope' to 24bit, 192kHz digital linear PCM audio, it's important to remember that it introduces a new audio surround format, namely six channel sound in uncompressed 24/96 PCM (using Meridian Lossless Packing - which is a compaction, rather than a reduction, algorithm) too. This is arguably the highest theoretical sound quality that domestic multi-channel can achieve. 

This offers interesting creative possibilities - not only will discs offer a straight analogue-to-digital conversion of the original stereo two-track analogue masters (obviously digital recordings can only be upsampled, rather than converted), but a 5.1 mix too. This has to be made in the studio from the original multi-track tapes - essentially 'creating' a new interpretation of the musical work, in a way never previously heard. 

It also gives space for the artists to get closer to how they wanted the original mix to sound. Queen's Bryan May, for example, is said to have taken the opportunity of the new release of 'A Night at the Opera' to 'correct mistakes in the original recording'. The repercussions of this are many - we may well be in for a raft of multi-channel remixes and a whole new software sales boom as the world goes 'surround sound' on the back of the DVD movie boom.

Title: Hotel Califiornia , Artist: The Eagles Formats: DVD-A; 2 channel, 5.1 , 24/96, DTS, Dolby Digital, Catalogue # 60509-9 

Everyone and his dog has a DVD video of 'Hell Freezes Over', but it's taken a surprisingly long time for an Eagles DVD-A to appear. Unsurprisingly it's the band's most famous, but cries of 'cynical cash in' will be quietened when you look at the strength-in-depth of this release. 

This 1977 Grammy award winning paean to seventies South California is brilliantly recreated with a choice of 24/192 2-channel mix (derived from the original analogue two-track master) and a 5.1 channel surround (24/96 using MLP), by original producer/engineer Bill Szymczyk and surround expert Elliot Scheiner. 

This was downmixed from the original 24-track analogue tapes via a Sony 3348 48-track digital recorder with dB Technologies 24-bit 96kHz Blue series A/D converters. The disc also contains 448kbps Dolby Digital mix and DTS alternatives, so even standard DVD video machines will play it (although not to DVD-A resolution). 
 
The DVD-A 5.1 mix sounds amazing, gently deploying discrete sounds in the centre channel, allied to subtle rear channel depth fills, bringing the guitars right to the sides of the rooms. True, there are a couple of dodgy all-around-the-room pan rolls (which is probably how they'd have mixed them in the seventies too, truth be told!), but the overall 5.1 mix is superb. 

Fidelity of both the multi channel and stereo mixes is excellent - my Michell Orbe playing a Japanese vinyl pressing of the album was given a close run by a Pioneer DV-747A DVD-A player. The vinyl pressing was slightly more musical, with better accents and phrasing on the guitar work, but the silver disc displayed fantastic depth and breadth. The only question mark is slightly audible clipping on 'Life in the Fast Lane'.

SACD MULTICHANNEL
Another new surround sound format arrived with the advent of Super Audio Compact Disc. While unabashedly a music format (unlike DVD, of course), its co-creators Sony and Philips were enthusiastic enough about multichannel to make it a key part of the specification.

It runs up to six channels at the full DSD bitrate, and accordingly the full sound quality is possible, and many discs also carry a standard Red Book layer readable by existing Compact Disc spinners. Like DVD-A, it offers a whole vista of possibilities for multichannel remixes and reissues, and unlike DVD-A is readable in a standard CD player (in two channel CD quality, of course).

Whether this is better than DVD-A 5.1 surround (using 24/96 packed PCM) is a contentious issue to say the least. Suffice to say that the two respective formats do have different technical specifications. While DVD-A multichannel runs out of bandwidth at 48kHz, SACD multi is claimed to stretch up to 100kHz thanks to its brickwall-filterless Direct Stream Digital (DSD) coding system. 

While this isn't the place to get into the relative merits of DSD vs. PCM, suffice to say that SACD multi is theoretically capable of superb sound. Right now, the real limiting factor is the quality of the recordings, SACD transfers and mixes, and of the SACD decoders and DACs themselves.

Title: Interactions, Artist: Acoustic Triangle, Formats: SACD Multichannel,   SACD 2- channel, CD, Catalogue: # SABCD 5012

The SACD format is growing fast - in some markets at least - and multichannel is an obvious allure. This hybrid release on the audio-b label contains stereo CD, stereo DSD and surround DSD mixes - and can be played on any silver disc player as a result (in CD quality). 

The CD and DSD layers are physically separate, and within the DSD layer there are three individual partitions containing the two channel and multichannel mixes, along with an additional text and graphics area.
 
Acoustic Triangle is formed by the respective talents of Malcolm Creese (double bass), John Horler (grand piano) and Tim Garland (soprano and tenor saxophones and bass clarinet). Interactions is an album of "melodic modern jazz with European classical influences", and very interesting it is too - I'd call it Debussy meets Dexter Gordon. 

Musically adventurous but loving all the same, the content quality is undeniable and the sound is utterly exquisite. In both 2-channel and 5.1 mixes, you get a cathedral-like acoustic in which you sit aghast and agog. 
 
In truth, if your surround system is properly set up, it's quite a lot more impressive than the stereo mix - but either is quite stunning. That grand piano is beautifully deep and sonorous, while the double bass seems to go down to the centre of the earth itself. 

Saxes sound quite unlike anything you'll get from CD - smooth but raw and breathy. Best of all though is the sound of St. George's in Bristol - the recording venue - which is amazingly spacious, and all the more atmospheric in multichannel mode. Superb.

MULTI CHOICE - THE VERDICT
On a purely practical level, surround-sound is not for everyone, as more physical space is required for all the loudspeakers and in the modern world we need as much space as possible. It's also still early days. Properly done, multichannel SACD and DVD-A can really enhance the musical enjoyment of your favourite albums - there really is more to surround sound now than cheesy movie effects. 

The problem is the paucity of titles available (and the sometimes dubious mixing techniques). In this respect there's a real feeling of deja-vu echoing the early days of Compact Disc. Indeed, Vivante's Shaun Ormond says the worst thing about the software is the sheer conservatism of the titles being drip-fed to audiophiles (although a few specialist classical labels such as Hyperion and Fone are releasing imaginitive SACD titles). "It's all safe seventies rock music, like CD all over again". Quite so, but time is on our side.

Thanks to Vivante Music Ltd (01293 822186) for supplying the review discs. Check out their website at www.vivante.co.uk for the latest high resolution digital software.