The benefits of watching a movie or listening to music in a 5.1-channel home theatre are undeniable. A well mixed movie soundtrack can make you feel like you’re part of the on-screen action. A well mixed concert disc can place you right in the audience.

Although 7.1-channel AV receivers have been available for a number of years now, few movies were made with discrete 7.1-channel soundtracks and few consumers bothered to set up the additional back surround channels because of the space requirement at the rear of the room.

Today, two new technologies are promising to enhance the audio aspect of our home theatres by introducing additional audio channels – this time at the front of the room. First up is the Dolby Pro Logic IIz format which adds two front height channels. Then there is the Audyssey DSX which provides a pair of wide channels as well as a pair of height channels. Both new technologies use the information from the existing 5.1-channel soundtracks found on DVDs and Blu-ray discs to create the new channels – the additional channels are not discrete. AV receivers with processing for these new technologies are just starting to appear in stores. Earlier this fall Editor-in-Chief Suave Kajko and myself asked Denon to send us their AVR-4310CI receiver ($2699) which comes with both technologies on board, so that we could put the new formats to the test. At the time of this writing, Onkyo was the only other manufacturer to offer an AV receiver with Dolby Pro Logic IIz processing (but no Audyssey DSX).

Dolby Pro Logic IIz

Dolby Pro Logic IIz aims to enhance the sound in your home theatre by adding two front height channels. These additional speakers are positioned above the front left and right speakers. The technology works by identifying spatial cues that are present in all audio content including movies, stereo and 5.1 broadcast TV, music CDs and video games. Dolby Pro Logic IIz examines all the channels but derives the non-directional, spatial cues only from the rear channels. It then processes ambient sound and amorphous effects such as rain or wind and plays them in the front height channels. Dolby Pro Logic IIz’s goal is to produce greater immersion than a standard 5.1-channel system provides by adding a spacious, vertical sound field.

Dolby Pro Logic IIz supports discrete height channels meaning that movie and video game producers could design content that directly utilizes these new channels. Currently however, content with discrete height channels does not exist.

Audyssey DSX

Audyssey Laboratories’ latest DSX (Dynamic Surround Expansion) technology is a scalable system that adds new speakers to “overcome the spatial sound rendering limitations faced by 5.1 surround sound systems”. DSX creates additional channels to augment 5.1 systems with the correct direction, time of arrival and frequency response characteristics and promises to achieve a seamless and expanded soundstage. The research, spearheaded by Audyssey Chief Science Officer, Tomlinson Holman and Kyriakakis showed that the properly controlled sound coming from a direction slightly wider than the front main speakers is the most important cue used by human perception of soundstage width. Following width, the second most important information comes from height channels that help define soundstage depth. DSX is a scalable solution, which builds on a 5.1 setup by providing a pair of wide channels and a pair of height channels to render the additional information. DSX also provides Surround Envelopment Processing which promises to improve the blend between the front and surround channels for a seamless and immersive soundstage.

The Setup

You could feel the anticipation in the air when we got together on the test day. We set up the Denon receiver to drive a 5.1-channel Elac 200 Series speaker system and used the PlayStation 3 connected with an HDMI cable as the source. The Denon AVR-4310CI is a 7.1-channel receiver, hence it allowed us to add two speakers to the system – we had to choose between the height or width channels. Therefore we tested three scenarios: Dolby Pro Logic IIz with the height channels, Audyssey DSX with the height channels and Audyssey DSX with the width channels. By the time you read this, a new Denon AVR-4810CI 9.1-channel receiver will be available, which will be able to power both the height and width channels simultaneously when using the Audyssey DSX.

Prior to our listening tests, I had the pleasure of spending a number of days living with the Denon AVR-4310CI connected to my existing 5.1-channel setup. I found the AVR-4310CI to have one of the most intuitive graphic user interfaces (GUI) on the market allowing for a quick and painless setup. The GUI is also the best looking one I’ve seen to date, thanks to the fact that it’s displayed in high definition. This was the first time that I used the Audyssey MultEQ XT tool on-board the receiver to calibrate my system – previously my system was calibrated using the Audyssey MultEQ. I was glad to learn that MultEQ XT offers a phenomenal jump in performance from basic MultEQ. The improvements in my room were a more spacious soundstage and unbelievable subwoofer integration. Low level detail and bass tonality was bang on.

On the test day, we expanded the 5.1-channel Elac speaker system by adding two KEF iQ3 bookshelf speakers in the height positions – flanking the main floorstanding speakers, six feet up in the air and pointed down at the listening position. Then the system was re-calibrated using the MultEQ XT tool. For each of the three tests below, we watched selections of scenes from various Blu-ray movies including Dark Knight, 12 Monkeys, Gladiator and Braveheart. Do the additional channels make a significant impact or is this just an attempt to sell more speakers, cables, etc? Let’s take a listen…

Dolby Pro Logic IIz Height Channel Test

With Dolby Pro Logic IIz processing engaged it didn’t take us long to come to a conclusion that while some audio effects were enhanced, the overall audio was slightly compromised. Yes, the soundstage now contained a height component and sounded more immersive. With certain effects such as rain, spinning helicopter blades and whistling wind, the results were beneficial – we did feel more enveloped by the audio. However, the addition of the height channels also made the front soundstage sound more congested and less natural than the movies’ original 5.1 soundtracks. Certain effects that shouldn’t be present in the height channels, such as cars driving by, at times ended up there. Other sounds, instead of smoothly panning across the front soundstage resulted in a slight “roller coaster” sound across the front of the room.

It is important to understand that Dolby Pro Logic IIz, or Audyssey DSX for that matter, do not attempt to provide a sensation of sound (such as an airplane) flying over your head. The only way to achieve this would be for the movie to contain discrete height channels encoded in the soundtrack. Instead both these formats are using the existing 5.1-channels of audio found on movie soundtracks and attempt to produce a greater sense of envelopment.

Audyssey DSX Height Channel Test

Our experiences with the Audyssey DSX height processing were very similar to the Dolby Pro Logic IIz height tests. Instead of enhancing the sound, the addition of the height channels resulted in an unnaturally congested front soundstage. We also found that the height channels were not as well integrated into the overall soundstage as we would have liked to see.

Audyssey DSX Width Channel Test

For this part of the test, we moved the KEF iQ3 bookshelf speakers to the wide positions and re-calibrated the Denon AVR-4810CI with MultEQ XT. In this configuration, the tweeters of all of the speakers in the front of the room were all at the same height.

After watching a few short clips from the same movie selections, the benefits of the width channels were immediately clear. In the opening scene where the crooks are traversing from building to building via wire and grappling hooks, the low level detail was phenomenal. Dialogue was more intelligible and bass information was full and well rounded without being overbearing. The soundstage had opened up dramatically without bringing attention to the two width channels. The width channels were integrated very well into the soundstage – the sound travelled seamlessly between the channels. This performance improvement was akin to what I experienced going from two channel SACD to multi-channel SACD. Later in the film, the car and truck chase scene had incredible dynamics without ever stressing the system. The 12 Monkeys Blu-ray has a very subtle sound design and with the width channels engaged, every little nuance was audible, increasing my enjoyment of the film. The scene where Bruce Willis is sitting in his cell and his neighbouring prisoner’s voice circles around him was uncanny in its intelligibility and accuracy. Gladiator and Braveheart both have scenes containing delicate subtle sounds as well as large scale battle scenes, and both benefited from the enhanced, wide soundfield.

Following the main test session with Suave, I listened to a number of high resolution music selections on my own. On The Last Waltz Blu-ray disc, the uncompressed 5.1 PCM soundtrack sounded as good as some of my most enjoyable multi-channel SACDs. Garth Hudson’s virtuoso keyboard playing and Levon Helm’s drumming had clarity that I had never heard despite viewing this Blu-ray disc many times before. The bass work of Rick Danko had such great tonality that I heard decay that never existed before.

Given how good The Last Waltz sounded, I decided to try a few multi-channel SACDs. The Who’s Tommy, Beck’s Sea Changes, Elton John’s Honky Chateau and Dire Strait’s Brothers In Arms were all dramatically improved. The mixes opened up, every sonic element was properly reproduced and located within the soundstage, with the trailing edges of decaying notes more evident.

In Conclusion

There is no question that the promise of a more immersive surround sound, with additional height and width components, makes us wag our tails. However our experience with the extra height channels and both Dolby Pro Logic IIz and Audyssey DSX processing was less than enthusiastic. On the other hand, the addition of the width channels combined with Audyssey DSX processing did enhance our enjoyment of movies and music.

So will either of these two formats capture the attention of a mass audience? It’s unlikely. The biggest challenge for consumers will be finding enough space for the additional speakers. Many consumers have a difficult enough time placing five speakers plus a subwoofer. However, home theatre enthusiasts that have large enough rooms and don’t mind being surrounded by additional speakers may want to try the addition of the wide channels.

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