Product Review - Dolby Surround Pro Logic II - The Technology and the Sound - March, 2001

Brian Florian and Stacey Spears

THE TECHNOLOGY (by Brian Florian)

Introduction

While for decades the term "Stereo" has implied two-channel/two-speaker audio systems, this is not really accurate. "Stereo", in the strictest sense, implies any reproduction system with two or more channels. The dawn of commercial stereophonic sound was achieved not in the music recording industry, but in the movie theater. The 1940 release of Fantasia ushered in a then new audio experience for the audience: 4 channels of audio through a system named "Fantasound". By the 50s, movies had become big business with larger and wider film formats in development to thrill audiences. In addition to having a better picture, the larger films had more room for audio. The 1953 film "The Robe" is recorded as the first CinemaScope release with 4 channels of magnetic sound right on the film strip, the technology being virtually identical to today's cassette or open reel tape, with 2 channels going in each direction. This landmark was quickly followed with "Oklahoma" whose 70mm ToddAO release featured 6 channels of magnetic sound. These events formed the catalyst for the development of 6 track magnetic sound on 70mm film, a practice that would endure for decades.

But by the 1970s, the grand 6-track soundtracks of the 50s and 60s were all but doomed: 70mm prints were too expensive, the magnetic sound (literally) wore off after repeated runs, and there was not enough room on 35mm prints to do much of anything. By the 70s, movie sound was back to dull mono. But in 1975, Dolby introduce the sound format Dolby Stereo. On the ubiquitous 35mm release prints, it is possible to squeeze in two optical soundtracks, call them Left and Right. The Dolby Stereo system also records, in those two channels, sound for a center channel and a surround channel (see technical explanation below), thereby delivering 4 channels via a 2 channel carrier. The system was simple in its implementation, it fit on inexpensive 35mm prints, and was compatible with mono playback systems. Surround sound had come to the masses, and to this day, there is hardly a movie released which does not, as a minimum, have a Dolby Stereo soundtrack.

One could almost say that this wonderful hobby we all enjoy was born of a coincidence. LaserDisc, Stereo VHS (analog and Hi-Fi), and even stereo TV broadcasts, all featured sound delivery with two channels. When a movie was transcribed to one of these mediums, the Dolby Stereo soundtrack, itself being carried by two channels, came along for the ride. The center and surround channel were just waiting to be separated back out, and the full dimensionality of the theatrical soundtrack realized.

In 1982, Dolby licensed a consumer decoding system for Dolby Stereo soundtracks named Dolby Surround, and home theater was born. Later in 1987, Dolby licensed a much more advanced system for decoding the soundtracks named Dolby Surround Pro Logic (or Pro Logic for short). Originally a very expensive technology found only in the most up-scale consumer hardware, it was not long before all of its complex functions could be implemented on an integrated circuit (IC), bringing home theater to the mass market.

But how does a Dolby Stereo soundtrack place additional channels in the left and right tracks, and how does the decoder know which sounds belong to which channel? To understand how Dolby Stereo is decoded, we must first understand how it is encoded.

The Dolby Stereo Soundtrack

In Dolby Stereo there are 4 channels: Left, Center, and Right (across the front), and a single surround channel (produced by speakers all around the audience in a theater or two speakers to the sides of the listener in the home). We start our explanation from these 4 'stems'.

The Left and Right channels are the carriers of the other two. That is, nothing special is done to these two input stems. They are the basis for what we will call LeftTotal and RightTotal, once the center and surround information have been added to them. This system is called a Matrix.

The Center channel stem is added equally to the Left and Right, but reduced by 3 dB so as to maintain constant total power when being carried by two channels as it is.

The surround channel is also input equally to both the Left and Right channels, but each half gets a 90⁰ phase shift opposite from each other. The surround channel information that is in Left and Right therefore ends up being 180⁰ to each other. In other words, they are totally out of phase. Before getting added to the soundtrack, it gets a -3 dB reduction (for the same reason as the center), is then filtered to the frequency range of 100 Hz to 7 kHz, and undergoes a form of Dolby B-Type noise reduction.

Quick side bar: Already one can see the genius of the Matrix system: All sounds are present in the LeftTotal/RightTotal carriers. When played back over a conventional 2 channel system, the center channel will be reproduced as a phantom image between left and right for persons seated in the center (the audiophile 'sweet-spot'). The surround channel will take on a diffuse character thanks to its out-of-phase nature.

The simplest way to decode a matrixed soundtrack such as Dolby Stereo is a simple passive system, as was implemented with Dolby Surround. In it, LeftTotal and RightTotal are passed unchanged to the Left and Right outputs. With no center channel output, the system relies instead on a phantom image between the left and right speakers. To extract the surround, LeftT and RightT inputs are passed through a differential stage ('subtracted' from one another).

While simple at the core, any matrix system is challenged by leakage from one channel to another. On the surface, one can see that there is near perfect separation between left and right channel information as they are on separate carriers. The separation between center and surround is likewise near perfect, as surround information will by nature be phase-inverted 180⁰ and cancel itself out from the front left/right speakers. Likewise the center component going through the surround stage will get shifted 180⁰ and cancel itself out. But between any two adjacent channels, the perceived separation will be at best 3 dB. The surround channel fortunately is predominantly an ambiance channel, its sounds being omnipresent in nature. But to improve the perceived separation, the Dolby Surround decoder performs some processing of the surround channel, namely 7 kHz low pass, delay, and noise reduction.

The 7 kHz low pass at input is of course applied in anticipation of the 7 kHz low pass in the decoding process. It exists in the decoding stage because phase shift anomalies in the 2-channel delivery systems become more severe with increasing frequency. In other words, there is greater chance for decoding errors in the higher frequencies. Dialogue sibilance is a terrific example of high-frequency leakage from front to surround which would be particularly distracting. The band limiting of the surround channel is far from objectionable from a fidelity point of view since the channel is intended to deliver a diffuse surround sound effect, not a localizable point source.

The delay circuit capitalizes on the Precedence or Haas Effect whereby if an identical sound comes from two sources, but one begins at least 10ms (milliseconds) sooner than the other, our brain will accept the sound as only coming from the first source. Leakage of front information to the surrounds is greatly minimized by this psycho-acoustic phenomena.

If we were to simply and passively play back the center channel by summing LeftT and RightT, the result would not be ideal. Consider the most classic example of a front soundstage dilemma: We have dialogue from the center and music from the left and right. Because the center channel is the sum of the left and right, the music will also be output from the center channel. Likewise, because the center channel is in leftT and rightT, it will also be output there. A passive center signal will therefore tend to narrow the perceived stereo effect considerably.

What to do, what to do?

Directional Enhancement!

The Pro Logic decoder, a direct descendant of the cinema Dolby Stereo decoder, is best thought of as a passive decoder followed by an active matrix which provides directional enhancement though a constant power concept.

Gain Riding was used in many early matrix systems including some ill fated music systems of the 60s and 70s. In such a system, the decoder detects which signal is dominant (in our example, the dialogue) and reduces the gain of the other channels accordingly. Of course, we hope that the dominance of the dialogue masks the fact that the music has been reduced. If left to itself, gain riding fails miserably in a dynamic environment where dialogue is starting and stopping: The gain of the left and right channels are bouncing up and down in response, producing a distracting "pumping" of the sound.

More successful is the concept of signal canceling. In the case of our center being dominant (the dialogue), the decoder takes the Left signal, phase inverts it 180⁰, and adds it to the Right output. The inverted center channel component from the left cancels out the center channel component in the right, eliminating the center channel component in the right output. The reciprocal is performed on the Left output. But we still have music from both Left and Right in the center, not to mention the left and right now carrying a copy of each other. But unlike gain riding, the overall level of the soundtrack can be maintained.

At the heart of Pro Logic then is Signal Dominance Detection. As a single channel becomes dominant, the remaining sounds are redistributed via signal masking as described above, keeping the overall level of the soundtrack constant, but providing appropriate directional enhancement where and when it is needed. The Pro Logic decoder then has two modes of operation, passive and active, based on the presence of a dominant signal.  It is passive until a dominant signal is detected, at which time it goes active, applying directional enhancement.  Pro Logic's active matrix looks at the relative level and phase of its input, and sends the information to VCAs (Voltage Control Amplifiers) to control the level of antiphase signals (the "inverted copies") applied to each channel. This system has come to be known as "feed forward" in that the enhancements are applied looking forward down the decode line.

Dolby Surround Pro Logic II : The next level.

Introduced last year, Dolby Pro Logic II is an improved, more intelligent matrix decoder.  So improved is its decoding, that it succeeds where Pro Logic performed poorly, i.e., playback of non-encoded material such as conventional 2-channel music.  That's not to say it is a music-only application, but it certainly makes for a new and wide appeal.   Conventional Pro Logic decoding lends itself perfectly to motion picture soundtracks.  The surround channel is predominantly diffuse ambiance, and the bulk of the soundtrack is focused to coincide with the visual front and center.  It is this "center heaviness" that many music enthusiasts find objectionable with 2 channel music through Pro Logic.

In Pro Logic II, the most significant technical difference from Pro Logic is that it incorporates a "feed back" design, in that the directional enhancements are applied back to the input of the active matrix.

To illustrate how Pro Logic II improves upon Pro Logic, consider a sound placed by the artist to image at 'half right', between the center speaker and the right speaker. This results in the sound being greater in RightT than LeftT. Because of this inequality, the passive decoder will not remove all of this front signal from the surround output.

To achieve full cancellation of this signal not wanted in the surround output, Pro Logic II servos (negative feedback) the inputs to make them equal. VCAs on each input to the surround decoding stage share a common control signal to maintain equal input to the surround stage. In our example of the "half right" sound, the RightT signal going to the surround decoder will be lowered a little while the LeftT will be raised a little so that they perfectly cancel each other out at the surround decode stage.

These same "balanced" signals are also used to feed the center decode stage, but are added rather than subtracted from each other to yield the center signal.

Because it is controlling the Left and Right feeds, this servo is known as the Left-Right axis. There is a similar servo which operates independently on the Center-Surround axis.  The net result is that Pro Logic II responds faster and is more accurate than its predecessor.

Where a Pro Logic decoder sends a single surround signal to two speakers (in other words, mono), Pro Logic II decodes independent left and right surround outputs (in other words, stereo).  Again, back to detecting signal dominance, the Pro Logic decoder has four cardinal vectors along which it is equipped to detect signal dominance:  Left, Right, Center, and Surround.   Pro Logic II simply includes two additional cardinal directions to detect signal dominance on, and derives its two surround outputs from these.

In addition to improved technology at the decode level, Pro Logic II incorporates additional features over Pro Logic:

• Bass management, made ubiquitous by the proliferation of Dolby Digital, is now a required part of the package.
• While Pro Logic II offers a "Pro Logic" mode which includes the band-limiting of the surrounds, in its native mode, the surrounds are full range and are independent Left/Right outputs.
• An optional "Width" control may be incorporated by the manufacturer (the receiver or processor manufacturer).
• An optional "Dimension" control may be incorporated by the manufacturer.
• An optional "Panorama" control may be incorporated by the manufacturer.

The "Others"

While Pro Logic II is the first system to incorporate the feedback design outlined above, there have been several other matrix decoding systems floating around, such as Circle Surround, Logic 7, and more recently DTS:Neo 6.1.  Each of these have their own little twist on the passive decode scheme, though the basic principles are all the same.

- Brian Florian -

 

IN PRACTICE (by Stacey Spears)

So, how does it sound?

Now that we all have Dolby Digital, DTS, and maybe even DVD-A or multi-channel SACD, which give us full range discrete sound in 5.1 channels, what are we supposed to do with our hundreds of millions of old two-channel CDs? And what about our VHS movie collections, FM radio, and TV? Dolby has the answer, with Pro Logic II, giving full range stereophonic sound even in the rear, and Meridian, being a world leader in consumer electronics, is the first to deliver. The result? WOW!!! . . . What a sound!

I received an e-mail around Christmas, 2000, from Bob Stuart (Meridian's President) asking me if I would like to get an early listen to Pro Logic II (PL II). Of course, I jumped at the opportunity. In fact, I have been enjoying PL II since Santa Claus took his sleigh ride.

It has been a long time since I have listened to a matrix encoded format. I have been spoiled by Dolby Digital (DD), just like you. One of the characteristics I noticed right away in PL II was the amount of information in the surround channels. At first I found the levels to be louder than I was accustomed to. In fact, on music, I thought it was too loud.

My surround speakers are full range floor-standing speakers. I have them directly to the side of my listening chair. They are sitting on top of cement cinder blocks to raise them slightly above ear level. I have a fireplace, which is not used, located 2� behind my listening chair. I have three full range speakers up front, and I am currently not using any subwoofers.

I spoke with Roger Dressler, from Dolby, about the surround levels. He asked me how I had set the levels, what type of speakers I had, and their height. Apparently, the way I had been calibrating my surround levels was not quite correct. So, I thought I would take the time to pass along this information.

I have always sat in my primary listening chair, held my arm straight out in front of me with the SPL meter pointing straight up. It turns out that when the levels are calibrated this way, the surround level ends up being 1-2 dB higher than it should. The correct way to set the level, according to Roger, is to have the meter in the same location your head will be. Of course you need to keep your body out of the way. This is a little difficult to do with the Radio Shack meter, though it is possible. Instead, I broke out my dusty Audio Control Spectrum Analyzer. It has a much more sensitive SPL meter built-in. I put its microphone on a stand and placed that on my chair. I then got far enough away and re-setup all of my levels. This made a noticeable difference, as the surrounds were not nearly as loud. The diagrams below show the correct and incorrect way to hold the SPL meter when calibrating sound levels of your speakers.

Of course there is more to the surround than just the level. In the discrete multi-channel world, the only information coming from those surround speakers is what the film makers intended. In the matrix world, you often get some leakage from other channels. This made me think back to the days when DD was first introduced, especially around the time "Forrest Gump" came out on Laserdisc. Many people were upset with Forrest because there was little to no surround information on the DD soundtrack . . . that and the fact that there are no chapter breaks on the disc. The PCM track had lots of ambient noise in the surround channels. Well, the filmmakers did not want the audience to be distracted by the surround channels. They wanted your attention focused on screen. They did not have a tight control on the matrix encoding found on the PCM track.

The point I am getting at is that we are now used to discrete sounds in all channels, and when you go back to matrix with PL II, using a 2-channel source (such as a CD), you will find the surrounds to be a bit more active.

If you switch between PL, PL II, and DD, you may find that there is a change in volume. This is a complex subject that we will cover in a later article.

Pro Logic II options

PL II offers two different decoding modes: Music and Movie. With PL II Music, there are 3 optional parameters: Dimension, Panorama, and Width. The range of adjustments mentioned below are based on the Meridian 861 and may be different for surround processors and receivers from other manufacturers.

Dimension is used to adjust the front-to-rear balance in the room. The adjustment has 7 possible positions. The default position is 0 which has the balance equal. A setting of +3 puts the balance toward the front of the room and a setting of -3 puts the balance to the back of the room. I played around a bit with this setting. Roger suggested pushing the balance more towards the front if I did not like the amount of surround information. After extensive playing, I settled on the default value of 0.

Panorama is used to wrap the sound field around you. You have two options, On or Off. The default is Off. It took me a long time to actually detect this in action. If the surrounds are busy, you don�t always notice the change when you turn Panorama on. I have since found several good examples, and while I do get some interesting side wall imaging, I prefer the Off position. This is one parameter where the location and type of side speakers will play a big role in the overall appreciation of it.

I found the best examples where there was an instrument on one side of the room or the other, and the surround activity was minimal. The opening and closing of Minority, which is Track 11 on the Greenday CD �Warning�, is a good demo of the Panorama effect. The track begins and ends with Billie Joe playing a guitar solo in the right front speaker. If I turn on Panorama, he moves from the right front of the room to the side of my room. Another good example of this is with the old Wild Cherry song, "Play the Funky Music."

Width is a center spread adjustment. The default value is 3. A setting of 0 sends most of the information to the center channel, and a setting of 7 is full left and right only. This provides a phantom center image. I usually found either 3 or 4 to be the best setting. This was with a center channel speaker that is identical to the left and right.

In addition to the optional items above, Music Mode has the following characteristics:

• There is no delay added to the surround channels by default. You can adjust the delay from 0ms to 15ms.
• Autobalance mode is off by default. Autobalance tends to steer vocals toward the center channel. This is not always desired in music because a vocalist can be placed off center on purpose.

The only option available in Movie Mode is a Pro Logic Retro option. The default value is Off. When this option is turned on, the surrounds are once again mono and they are bandwidth limited to 7 kHz. They include this mode for backwards compatibility. (This will allow PL II decoder makers not to need a separate PL mode.)

In addition to the optional item above, Movie Mode has the following characteristics:

• There is a 10ms delay added to the surround channel. You can adjust the delay from 10ms to 25ms. (The original Pro Logic has a default delay of 15ms.)
• Autobalance mode is on by default.

Meridian has chosen to keep their original Pro Logic mode, and they also offer the Retro mode in PL II. The original Pro Logic mode offered by Meridian has the ability to provide mono rears or Meridian�s propriety steered rears.

Meridian has also implemented a third mode, PL II THX. This is the movie mode with THX processing added, and it includes the THX RE-EQ and Timbre Matching features.

Pro Logic II in action

PL II Music is something that grows on you. Or at least this is what happened to me, because at first, I was not impressed. To put things into perspective, I have been using Meridian�s Trifield DSP mode for a long time. Trifield is a passive matrix decoder, and there is very little information in the surround channels. The surrounds really just add ambiance to the room, which is extracted from the recording. PL II, in contrast, has aggressive surround channels that envelope you. However, the more I listened to PL II, the more I began to enjoy it.

The best way to describe PL II Music is fun. You are immersed in this larger-than-life sound field that manages to wrap itself around you. The soundstage upfront is vast. It goes from one end of the room to the other, and it stretches from the floor up to the ceiling. (I have a vaulted ceiling and I perceive this huge sense of space.) If you are a serious 2-channel aficionado, you may not like the effects of PL II. There are times when instruments or vocals end up in the surrounds. PL II will be a matter of taste. Of course, with processors and receivers that have it, you just turn the effect off when you don't like it, and listen in standard 2-channel mode.

While there were some songs that I think sounded strange in PL II, like Sweet Caroline, I found many others that were greatly enhanced by PL II. There were several tracks on the Destiny's Child CD "The Writings on the Wall", which include Bug A Boo, Jumpin, Jumpin, and Say My Name. Each of of these songs is high energy, and you really feel involved with the music as it wraps around you. Nelly's CD "Country Grammar" has two songs that I like, and also really work well with PL II. These are the title track Country Grammar and E.I. If you are not into RAP, then you may not care for these, but if you like this genre, you have never heard them like this! One last CD that I have to mention is "Hotshot" from Shaggy. Every song on this CD is great, but my current favorite is Angel. The previous CDs wrap around you, but this one keeps most of the action up front and just provides nice ambiance in the surrounds.

For those who may not know, PL II was created by Jim Fosgate. Jim is the same person responsible for the famous 6-Axis matrix decoder that was exclusive to the Citation line of A/V products, which included the Citation 7.0 and 5.0 surround decoders. My first experience with Jim�s products was the famed Fosgate Model 3A. (I actually had the Model 3 and later upgraded it to the 3A.) Unlike Jim�s previous work, which had a limited market do to specialty products, he wanted more people to be able to enjoy the fruits of his labor. What better way than to join forces with Dolby? Dolby is handling all licensing for PL II. This means that you can expect it to show up in products at all price points. I expect it will be a tremendous product for cars.

Personally, I am really excited about Jim letting Dolby handle the license for PL II. The one thing that I have always felt that was missing from the Meridian surround processors was a killer matrix decoder for movies. Music was never a concern previously because they had always offered Trifield.

PL II Movie is an improvement not only over Pro Logic but all other matrix decoding formats I have heard, and this includes 6-Axis, Logic 7, Circle Surround 5.1, and DTS Neo:6.

Other Matrix decoders

I thought it would be fun to see just how PL II compares with the other matrix decoders on the market. I managed to acquire several surround processors to make my comparison. What better way to tell you how PL II works on films than by telling you what it does different than the others?

I used the following processors to perform the comparison:

• Meridian 861: Pro Logic II Music; Pro Logic II Movie
• Theta Casablanca II: Circle Surround Cinema; Circle Surround Non-Encoded
• Lexicon DC-2: Logic 7; Music Logic
• Denon AVR-3801: DTS Neo:6 Cinema; DTS Neo:6 Music

My 861 is equipped with an IA40 multi-channel input card. This card has two pairs of 6-channel inputs. This allowed me the ability to connect two external processors to the 861 so that I could switch between them and PL II. I was only listening for matrix decoding artifacts, nothing more, so I was judging only the matrix enhancements each one provides.

I configured the Lexicon DC-2 with 5 full range speakers and no subwoofer. All speaker delays were set to 3� (three feet). This was the lowest value you could use. But since they are all the same delay setting, this was not a problem. The DC-2 has several options that allow you to customize to your liking. I left all of the settings in their default position. Some interesting ones to note are Soundstage and the Surround Roll-Off. Soundstage will actually attenuate the surround level based on source material.

Logic 7:

• Soundstage is set to Rear, which has 0 dB attenuation of the surrounds.
• Surround Roll-Off is set to 6.9 kHz. This is similar to the 7 kHz filter in Pro Logic. Remember, PL II has no filter. While I could have made the surrounds in Logic 7 full range, I chose to leave it in the default position. This is how Lexicon ships the product.

Music Logic:

• Soundstage is set to neutral, which has 3 dB of attenuation to the surrounds.
• Surround Roll-Off is set to 4 kHz.

I configured the Denon AVR-3801 with 5 full range speakers and no subwoofer. All speaker delays were set to 0.

I configured the Theta Casablanca II with 5 full range speakers and no subwoofer. The front three speakers had their delay set to 10ms, and the surrounds had they delay set to 15ms. The fronts allow a delay setting of 0ms to 10ms, while the surrounds allow a delay setting of 15ms to 31ms. I had no choice here, so I kept a note to myself should I experience any strange delays that the other three did not have. None were found.

I calibrated each processor to match the levels of the 861 using the DD tones on the Avia DVD. After this, I still had to adjust the volume so all of the processors where at the same volume. There seems to be a volume difference between matrix decoders, because all play DD at the same level. The Lexicon ended up being very close if not a tad higher than PL II. The Denon was actually a lot lower in volume, but easy to fix. The Theta was close. In the end I was able to match the volumes.

Test material:

• Best of Chesky Classics & Jazz and Audiophile Test Disk Volume 3 (They spelled disc incorrectly, not me.): Track 28, natural stereo imaging.
• Surround Test CD from Finlandia Records: Track 19, Noise panning (L-R-L 20Hz to 20kHz); Track 21, Stepped Noise Panning (20Hz to 20kHz).
• Tarzan DVD (Walt Disney): Chapter 8 (17:25 to 17:35)
• Star Trek First Contact DVD (Paramount): Chapter 2; Chapter 3 (6:01 � 6:09)
• Elizabeth DVD (Polygram): Chapter 2.
• Beautiful Girls Soundtrack: Track 14, Neil Diamond �Sweet Caroline�

The decoders really could be grouped into two pairs. First, PL II and Logic 7/Music Logic had similar behavior, and both provided an enjoyable experience.

The other pair was Circle Surround and Neo:6. Both of these matrix decoders did several things that I found distracting. They really broke the cardinal rule of decoding, namely that they brought attention to themselves. They tried really hard to let you know that the surrounds are discrete. I use the term discrete and not stereo because that is how I perceived them to be. I did prefer CS over Neo:6 in all cases.

I wanted a second opinion on Neo:6 because of my lukewarm impressions. so I enlisted the help of my roommate Aaron. Aaron is not an audiophile, but he does enjoy music and movies. He is an EE by trade. I first placed Aaron next to the left surround channel. I had him put his ear up to the speaker. I played the first 20 seconds of Sweet Caroline in PL II Music. After that I started the song over but switched to Neo:6 Music. Four seconds into the song, he asked my why it was clipping. I said, �Exactly!� He, being an engineer, said, "Well I can hear it with my ear to the speaker, but will I really notice it from the listening chair?" So Aaron then took a seat in the sweet spot. I repeated the track with PL II Music and he made no comments. I then started, yet again, in Neo:6 Music. About six seconds into the song, he looked at me and shook his head, like what were they thinking. This clipping sound did not happen on every CD I tried, but I would say it happened on over half of them.

Finlandia

The tracks I used on this CD are designed to check the phase and image uniformity across the three front speakers in a multi-channel system. However, they proved useful for testing a matrix decoder�s ability to properly place the sound. This is the same problem that happens on "Tarzan" with the Elephants' voices.

I tried both tracks in music and film mode on each processor.

Let's start with PL II, because it performed as advertised. On track 19, the sound panned back and forth from left to right at a constant level and speed. On track 21, I got the same expected results. The bursts appeared in the correct locations: Left, left-center, center, right-center, and right. The phantom images between the center and side speakers were well defined and were placed precisely between the speakers.

Logic 7 was a bit different. Track 19 also panned, but the sound appeared to arrive at the center a bit early. While it was at the left-center position, I could hear the center already on, but at a lower volume. As it passed from the center on to the right-center location, again the center took a little longer to go away. Track 21 had the bursts in the same location as PL II, where they belong.

Circle Surround was where things started to go south. Track 19 performed as expected with the exception of a perceived level increase as the pan swept across the center channel. The volume would bump up, then down again as it passed. Track 21 was also not as precise as the previous two. The left-center and right center bursts were pulled more towards the right and left speakers instead of imaging in between.

DTS Neo:6 followed in the same fashion as Circle Surround but the errors were more pronounced. Track 19's pan had the level anomaly as it swept across the center channel, but it was more abrupt. In Circle Surround, the sound went up and then down. In Neo:6, it went up and down too, but it happened very fast. Track 21 was also worse than CS. The left-center and right-center bursts were almost in the same location as the left and right bursts. Neo:6 could not present the phantom center image between the speakers.

Tarzan

The scene in "Tarzan" is a real world example of the "Finlandia" tests. Since this disc is a DD disc, I first listened to the scene in DD to know what it should sound like before I proceeded to listen to the matrix version. There was not a separate 2-channel mix on this DVD, so the DVD player down-mixed the 5-channel into 2-channels. Tarzan is a 5.0, not a 5.1 recording.

Before I move on, I need to describe my theater layout. I am using an 87� wide (100� diagonal) 16x9 screen. The front left and right speakers are located 6 inches from each side of the screen. I mention this because the artifact has less effect in my situation. I also used the mini-theater (family room system), which has a 27� diagonal 4:3 TV. The surrounds in this setup are 3� from each side of the screen.

In both PL II and Logic 7, the dialog of the elephants is properly placed. The left elephant dialogue is left-center, and the right elephant dialog is right-center. Both are more towards the center, but you get the idea. This places the dialogue in the same position as the onscreen characters.

Circle Surround appeared to be halfway correct. The images were pulled a little further to the left and right.

Neo:6 was just plain wrong! The left elephant was in the far left speaker and the right elephant was in the far right. With the 87� screen, this was not as bad because I have such a wide screen. In the case of the 27� TV, it just destroyed the illusion. I took my eyes off the TV to follow the sound.

Chesky

This is another fun CD. It has many examples of real spaces vs. created spaces. I chose track 28, which is their natural stereo imaging track. It has David Chesky walking around a micrphone, beating a tom-tom drum. The pan goes center to left, to back left, to back right, to front, and it repeats once more.

First up was PL II. In the music mode I got a sense of David walking across the front of the room, then completely around me and back to the front. The front to back went rather quickly. In PL II movie mode, there was better sidewall imaging on the left, but the back did not seem as real as PL II music.

Logic 7 and Music Logic were less impressive here. While David managed to walk across the front of the room, I never got the feeling he walked behind me. It felt like he walked around in front of me.

Neo:6 did well here. In Music mode, there was excellent sidewall imaging on the left side of the room. It sounded like David clearly walked across the left side of my room. The back pan went rather quickly, and there was no real right sidewall imaging. In Cinema mode, I had not only less left sidewall imaging but also less rear wall imaging.

Star Trek

I played two different tracks here. First was chapter 2 where you see Jean-Luc Picard being assimilated by the Borg. The other was in chapter 3, from 6:03 to 6:06. Here it has the USS Enterprise panning from the rear to the front. There is a whirling sound as the blue portions of the Enterprise come on screen. Sorry, not being a Trekke, I am not familiar with the proper names of the ships' parts. I first listened to these scenes in DD 5.1, and then I switched back to the 2-channel version on the disc.

In PL II, the opening of chapter 2 sounded very much like the 5.1 mix. It was very enveloping, and then the run down the hallway had voices all around. PL II did an impressive job. The chapter 3 scene with the pan was not exactly like the 5.1. In the 5.1, you hear the whirling come from the right and then left rear and a pan up to the front channels. With PL II, the sound appears to come from the front the entire time. Not at all distracting, just different.

Logic 7 was much like PL II, but perhaps there was a bit more surround info in the right rear channel. Not distracting, but I only noticed it because I played this same scene numerous times.

Neo:6 called attention to itself during the Borg scene in chapter 2. Instead of the stereophonic sound field, it felt like two different sound fields. I had the left half of my room and the right half of my room; it was as if Moses himself parted the sound field. During the pan in chapter 3, all of the whirling noise came from the right surround speaker. It completely called attention to itself. I actually took my eyes from the screen and looked over my right shoulder. I don�t think the filmmaker would want this.

Circle Surround was similar to Neo:6, though not as pervasive. In the Borg scene, I got a better sense of a cohesive sound field. The pan did wander to the right surround a bit more, but not enough to pull my eyes away from the screen. I did notice a bit of dialogue leaking into the surrounds.

I got a real surprise when I switched to the original Pro Logic, using Meridian�s steered rears. It actually sounded like the real 5.1 mix in this mode. There was little frontal action, so I only paid attention to what the surrounds were doing.

Elizabeth

Chapter 2 begins with a scene in a large cathedral. It actually opens with a roar from the previous scene where bodies were being burned. This sound quickly fades to the rear, and you hear the echo of the footsteps in the background. I used the 5.1 soundtrack as a reference, but then I used the 2.0 mix for the matrix decoders.

PL II again does well. This is the first piece where I noticed rear wall imaging. I actually had the sense of a large space behind me, even though in reality, my fireplace is just two feet back.

Logic 7 performs much like PL II. The roar fades, and then you are left with this wonderful rear wall imaging.

Circle Surround loses it here. The roar decides to take a trip to the right side of the room, and I get no sense of rear wall imaging.

Neo:6, like Circle Surround, loses it once again. There is absolutely no sense of rear wall imaging. I can detect discrete sounds coming from the left and right surround, but they never come together to form a cohesive stereophonic image. The roar actually dies off and goes to the left surround.

Moving On

Above, I gave a few examples of how each matrix decoder performed on a variety of material. While there were small nuances between PL II and Logic 7, both seem to be going in the right direction. I should note that I was running 4.0 software on the DC-2. I have listened to Logic 7 in the past with older software and had noticed the front sound field pump, but I did not notice any of that in this test.

Circle Surround and Neo:6 appear to be going the wrong direction. By that I mean they appear to be designed to call attention to themselves. As I said previously, I did not find Circle Surround to be as obnoxious as Neo:6. There were times when both would let dialogue leak into the surround, while PL II and Logic 7 kept the dialogue up front. There was one other characteristic I noticed with Neo:6, namely that the soundstage was unstable. It had a tendency to shift back and forth at times, as if it did not have an anchor.

I believe that PL II is one of most promising audio developments to occur in the last few years. THX Surround EX and other similar products are getting a lot of attention, but the fact remains they will have a limited market for a while, because we are all tired of adding speakers after the arduous conversion to 5.1. PL II works with your existing speakers, will add a new dimension to all those old CDs, and everyone can enjoy it right away!

- Stacey Spears -

� Copyright 2001 Secrets of Home Theater & High Fidelity
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