Audio for Home Theater and Multichannel Music [part 2]

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Left and Right Speakers

The left and right loudspeakers carry the majority of the film’s musical score and many of the effects. And if you aren’t using a subwoofer, nearly all the bass will be reproduced by the left and right speakers. Consequently, left and right speakers are often the largest speakers in a home-theater system. A subwoofer/satellite speaker system blends into home decor more easily than does a floor-standing, full-range system.

Left and right speakers can also be small units that sit on speaker stands or on an entertainment cabinet. If that’s the case, the small speakers must be used with a subwoofer to reproduce bass. The small left and right speakers reproduce the midrange and treble frequencies, and the subwoofer handles all the bass. Such a system, called a subwoofer/ satellite system, is ideal if your available space is limited, or if you want the left and right loudspeakers to better blend into your decor. Satellite speakers can be small and unobtrusive, and the subwoofer can be tucked out of the way. If you build the three front speakers into a wall in a custom installation, they will most likely be satellites.

Surround Speakers

The surround loudspeakers are completely different in design and function from left, center, and right speakers. Their job is to re-create a diffuse atmosphere of sound effects to envelop us in a subtle sonic environment that puts us in the action happening on the screen. Unlike front and center speakers that anchor the sound onscreen, surround speakers should “disappear” into a diffuse “wash” of sound all around us.

A good example of how surround speakers create an atmosphere comes from the film Round Midnight. Toward the beginning of the movie the character Francois is outside a Paris jazz club in a driving rainstorm, listening to Dexter Gordon’s character playing inside. The scene cuts between the intimate sound of the jazz club and the rainy Paris street. Inside the club, the sound is direct and immediate to reflect the cam era’s perspective of just a few feet from the musical group. When the Scene cuts to the street, we are surrounded by the expansive sound of rain, cars driving by, people talking as they walk past—in other words, all the ambiance and atmosphere of a rainy night in Paris. This envelopment is largely created by the surround speakers. We don’t want to hear the rain and street sounds coming from two locations behind us, but to be surrounded by the sounds, as we’d hear them in real life. The surround speakers perform this subtle, yet vital role in home theater.

Surround speakers envelop us by their design and placement in the home-theater room. They are best located to the side or rear of the listening position, and sever al feet above ear level. Because they don’t have to reproduce bass, surround speakers can be small and unobtrusive, and are often mounted on or inside a wall.

Dipolar and Bipolar Surround Speakers

Most of the surround speakers’ ability to wrap us in sound comes from their d design. Dipolar simply means that they produce sound to the front and rear equally. While front speakers have one set of drivers that project sound forward, dipolar surround speakers have two sets of drivers, mounted front and back. This arrangement produces a directional pattern that fires to the front and back of the room (see figure below). Because the surround speakers are positioned to the sides and fire to the front and back of the room, we hear no direct sound from them. The listener sits in the surround speakers’ “null”—the point where they don’t directly project sound. Instead of hearing direct sound from the surround speakers, we hear their sound after it’s been reflected, or bounced off, the room’s walls and furnishings. The surround speakers’ dipolar directional pattern makes their sound diffuse and harder to localize. You shouldn’t be able to tell where a properly set-up surround speaker is just by listening.

hpas_10-7.jpg The surround speakers’ dipolar radiation pattern results in the listener hearing their sounds only after being reflected from a room surface.

You may see surround speakers called either dipolar or bipolar. Although both produce sound equally from the front and rear, the bipolar speaker produces sound from the rear that is in-phase with the front sound. A dipolar produces sound from the rear that is out-of-phase with the front sound. In-phase means that the front and rear waves have the same polarity: When the front-firing woofer moves forward to create a positive pressure wave, the rear-firing woofer also moves forward. The opposite is true in a dipole: When the front-firing woofer moves forward, the rear-firing woofer moves backward. In a dipole, the front and back waves are identical, but have the opposite polarity Both bipolar and dipolar designs achieve the objective of enveloping the viewer/listener in the film’s aural ambiance, but the dipolar type is preferred because it creates a greater “null,” or reduction in sound, at the side of the speaker that faces the listener.

A true dipolar or bipolar surround speaker can’t be flush-mounted inside a wall. Instead, it must be mounted on the wall so it can radiate sound toward the front and rear of the room. Some surround speakers approximate a dipolar radiation pattern by mounting the drivers on an angled baffle. Although not true dipoles, these flush- mounted surround speakers accomplish the goal of creating a diffuse ambiance and fit unobtrusively in your living room.

The amount of sound produced by the surround speakers is adjustable through the receiver’s or controller’s remote control. Their volume level should be set SO that you never hear them directly, but if you turned them off, the soundfield would collapse toward the front. All too often, consumers set surround speaker levels too high; their thinking seems to be that if they bought speakers, they should be able to hear them.

Surround-Back Speakers for 7.1-Channel Sources

As described earlier, the Dolby Digital EX and DTS-ES formats add one or two additional surround speakers behind the listener. Dolby Digital Plus and DTS-HD are full 7.1-channel formats that require two additional surround-back speakers. THX recommends that two speakers be used, and that their radiation patterns be dipolar. The surround-back speakers are usually identical to the left- and right-surround speakers.

Subwoofers

A subwoofer is a speaker that reproduces only low bass. Subwoofers are usually squarish or rectangular cabinets that can be positioned nearly anywhere in the home-theater room. A good subwoofer adds quite a bit of impact and visceral thrill to the home- theater experience.

Most subwoofers for home-theater use are powered or active subwoofers. These terms describe a subwoofer with a built-in power amplifier that drives its large woofer cone. The powered subwoofer takes a line-level output from the jack marked SUB- WOOFER OUT on your A/V receiver or controller, and converts that electrical signal into sound. Because powered subwoofers have built-in amplifiers, they must be plugged into an AC wall outlet. (See Section 9 for more on subwoofers.)

Setting up a Home Theater

How a home-theater system is set up and calibrated has an enormous influence on the quality of the sound you hear. Just as with a 2-channel music system, ideal loudspeaker placement and careful attention to detail will reward you with superior performance. The acoustic principles described in the next section and in Section 12 apply equally well to a multichannel audio system.

Basic Setup

The first step in setting up your system is deciding where to install it. More than likely, the room where you watch television will become the home-theater room. But this room may have been arranged for casual TV watching, not for experiencing the full impact of what a home-theater system can deliver. Now is the time to rethink the room’s layout and consider making the home-theater system the room’s central focus.

The home-theater room should be arranged with the video monitor and front loudspeakers at one end, the couch or viewing chairs at the other. Ideally, the couch will be positioned partway into the room and not against the back wall. This location is better acoustically (excessive bass build-up occurs near the back wall), and allows the surround speakers to better do their job of enveloping you in the film’s soundtrack. Of course, the setup should provide room for the left and right speakers on either side of the video monitor.

The optimum viewing distance between you and the video monitor is determined by the video monitor’s size. The smaller the monitor, the closer you should sit to maintain the maximum image area in your field of view. Sitting too close to a large monitor, particularly a rear-projection set, exposes the pixel structure inherent in a video presentation. If you are watching high-definition programming on an HD set, you can sit much closer without seeing the pixel structure. The best viewing distance offers the largest possible picture without making that picture look grainy. A good rule of thumb is to sit three-to-four picture heights away from the screen. You should also try to sit no more than 15° off to the side of the video monitor. Plasma panels, with their wider field of view, maintain a good picture even when they are watched from an extreme angle.

Once you’ve decided on where the couch and video monitor will be positioned, you’ll need to determine the best place for your equipment. A simple home- theater system will have a VCR or hard-disk digital video recorder, A/V receiver, satellite receiver, and DVD player. These components can be easily accommodated in a TV stand or rack.

Acoustical Treatment

Before we get to the specifics of loudspeaker placement, here are a few guidelines on how to make your home-theater room sound better. First, if you have a bare tile or wood floor between you and the front three speakers, covering the floor with a rug is probably the single most important thing you can do to improve your room’s acoustics. The rug absorbs unwanted acoustic reflections from the floor, which improves dialogue intelligibility and adds to a sense of clarity. Similarly, absorbing the acoustic reflections from the side walls between you and the left and right speakers also helps you to get better sound. Bookcases and hanging rugs are both effective in absorbing or diffusing side-wall reflections. Generally, the front of the room should be acoustically absorptive, with drapes, carpets, and hanging rugs.

Conversely, the back of the room should be more acoustically reflective. Bare walls behind the listening/viewing position tend to reflect sound and add to the feeling of spaciousness generated by the surround speakers. The optimum condition is when the wall behind the listening position diffuses the sound. Bookcases and media-storage racks make great diffusers. The sounds produced by a movie theater’s array of surround speakers all reach your ears at different times, increasing the feeling of envelopment. But because a home-theater system uses just two surround speakers, we must help them achieve their goal by providing reflective surfaces near them.

Speaker Placement

Where speakers are located in your room has a huge influence on the quality of sound you will achieve. Correct speaker placement can make the difference between good and spectacular performance from the same equipment. If you follow a few simple speaker-placement techniques, you’ll be well on your way toward getting the best sound from your system. Correct speaker placement is the single most important factor in achieving good sound.

Surround-Speaker Placement

Let’s start with the most difficult of a home-theater system’s six speakers: the two surround speakers. As I said earlier, the surround speakers are usually dipolar. That is, they produce sound equally to the front and the rear of the speaker cabinet. Dipoles produce a “null,” or area of no sound, at the cabinet sides. Here’s a simple rule for positioning dipolar surround speakers no matter what the installation: Point the surround speakers’ null at the listening position. Never point the surround speakers directly at the listening position.

Ideally, the surround speakers would be located on the side walls directly to the side of the listening position and at least two feet above the listeners’ heads when seated. Dipolar surround speakers should never be located in front of the listening position, where they could be heard directly; the surround speakers’ sound should be reflected around the room before reaching the listener. This helps to mimic the sound of a movie theater’s surround array with just two speakers, and to create the envelopment that’s so important to the home-theater experience.

Keep in mind that reflections of signals from the front speakers are bad; reflections of signals from the rear speakers are good. Well-positioned surround speakers make a tremendous difference in the quality of the home-theater experience by recreating the sense of ambience and space we hear in a movie theater.

Surround-Back Speaker Placement for 7.1-Channel Sources

According to Lucasfilm, the surround channels are best reproduced by four identical dipolar speakers. The two surround speakers remain at their normal position (normal for 5.1-channel reproduction), which is 110°, or slightly behind the listener on the side walls. The surround back speakers are located at 150°.

The two surround-back speakers should be arranged so that their facing sides are in-phase with each other. That is, the side of the dipole that would face the back of the room if mounted on a sidewall should face toward the room’s centerline when the speaker is mounted on the rear wall. ‘l arrangement keeps the drivers of the two surround hack speakers that face each other in-phase, contributing to their ability to create an image between them directly behind the listening position. If you’re using a single surround-back speaker, position it directly behind the listener at 180°.

Center-Speaker Placement

Correct positioning of the center speaker results in better dialogue intelligibility, smoother movement of onscreen sounds, and a more spacious soundstage. As just mentioned, reflections from the front speakers that reach the listener work against good sound. This is particularly true of the center speaker, which carries the all-important dialogue. Because most center-channel speakers are mounted on top of a direct-view TV or rear projector—both of which are highly reflective—there’s the potential for unwanted reflections from the video monitor.

To reduce reflections from the center speaker, align its front edge absolutely flush with the front of the video monitor so that they form as smooth a surface as possible. This positioning reduces a phenomenon called d which is the re-radiation of sound when the sound waves encounter a discontinuity. (Specifically, diffraction introduces variations in the speaker’s frequency response.) Think of waves rippling in a pond: If you put a stick in the water, the waves will strike the stick and be re-radiated around it. The same thing happens when the sound from the center speaker encounters the “stick” of the video monitor: the monitor re-radiates that sound toward the listener, making the overall sound less accurate. That’s why making the center speaker flush with the front of the video monitor is so important (Fig.5 earlier).

High-end loudspeaker manufacturers carefully design their enclosures to reduce diffraction. You’ll notice that high-quality loudspeakers have smooth surfaces around the speaker cones. Some have rounded fronts and even the mounting bolts securing the individual drivers within the speaker are recessed to reduce diffraction from the speaker cabinet. The B&W 801 loudspeaker is an extreme example of an enclosure designed to minimize diffraction.

You should also tilt the center speaker down toward the listening position if it is mounted on a large rear-projection set, or on a direct-view TV positioned on a tall stand. If the center speaker is located below the video monitor, point it up toward the listeners. Direct the center speaker’s sound toward the height of the listeners’ ears when seated. Finally, be sure the center speaker is less than 2’ different in height from the left and right speakers, measured from each speaker’s tweeters.

Left and Right Speaker Placement

The left and right speakers should be pulled slightly in front of the video monitor and not be in a straight line with it (as some owner’s manuals erroneously advise). Positioning the left and tight speakers so that they form a gentle arc with the center speaker has two advantages. First, acoustic reflections from the video monitor are reduced. Second, the left, right, and center speakers are flow all the same distance from the listener. The sounds from each of the three front speakers will reach the listener at the same time.

The speaker-placement guidelines for 2-channel stereo presented in Section 12 apply equally well to the left and right speakers in a multichannel system.

Subwoofer Placement and Connection

Where the subwoofer is positioned in your room will greatly affect the bass smooth ness, clarity, and impact. An ideal—but often impractical—position is right next to the listening seat. This placement results in the listener hearing more of the direct wave- launch from the woofer and less of the woofer’s sound after it has been modified by the room (this phenomenon is described in detail in Section 12).

A rule of thumb says that for the smoothest bass response, don’t position a subwoofer at the same distance from two walls. For example, if you want to put the sub on the wall behind your video display, don’t put the sub mid-way between the two walls. The guidelines presented in Section 12 for achieving the smoothest bass from left and right loudspeakers applies equally well to subwoofer positioning.

Many subwoofers offer several ways of connecting the sub to the rest of your system. The first connection method uses the speaker-level output from your receiver. You connect speaker cables between your AVR and the sub, and between the sub and your left and right speakers. The subwoofer’s internal crossover splits up the frequency spectrum, filtering bass from the signal driving your left and right speakers. In this connection method, the crossover that divides the frequency spectrum operates on the high-level signal (one powerful enough to drive speakers).

The second, and preferable, method is to connect the AVR’s SUBWOOFER OUTPUT jack to the subwoofer’s line-level input. The AVR’s internal crossover (bass management) splits the frequency spectrum, sending bass to the subwoofer at line-level through the SUBWOOFER OUTPUT jack, and powering the left and right speakers from the AVR’s internal amplifiers. Note that this method requires that the subwoofer be of the active type, with an integral power amplifier to drive the woofer cone.

This second method avoids subjecting the signal driving the left and right speakers to filtering by the subwoofer. The result is cleaner sound.

A third subwoofer-connection method, used with a separate controller and power amplifier, puts the subwoofer in the line-level signal path between the controller and the amplifier. The controller’s left and right line-level outputs feed the subwoofer’s line inputs; the sub’s line outputs drive the left and right power amplifiers, but with bass removed from the signal by the subwoofer’s crossover.

Some subwoofers have separate PROCESSOR and LINE inputs. The PROCESSOR input (a single jack) accepts the subwoofer output from an AVR or controller; the LINE input is stereo, and is connected to a second output from your preamplifier. When watching movies, set the subwoofer’s input switch to PROCESSOR. When listening to music, set the sub’s input switch to LINE. This assumes, of course, that you prefer listening to music with the subwoofer engaged.

Calibrating a Home Theater

Once your system is connected, you’ll need to configure it for your particular room and speaker system. This is done through a series of menus or graphical icons generated by the A/V receiver or A/V controller and appearing on your video monitor. You use the receiver’s remote control to make selections from the onscreen display. Every A/V receiver or controller includes instructions for setting up your system; the following section explains why you make certain selections, and in what circumstances.

When you turn on your system for the first time, don’t be alarmed if you don’t hear any sound when you expect to. (This usually happens when I first set up a product for review.) Don’t turn up the volume to a high level and then start pushing buttons—when you push the right button, the sound will blast you out, possibly dam aging your speakers, your amplifier or receiver, and/or your hearing. Turn the volume to a low level and make sure the correct source is selected. Check to make sure the MUTE and TAPE MONITOR buttons aren’t pressed. The lack of sound is probably due to one of these three incorrect settings.

Bass Management

The first calibration step is configuring the receiver’s bass management settings for your particular loudspeaker system. Bass management describes a receiver function that diverts bass from small loudspeakers to the subwoofer, if the system uses one. The first step in system setup is telling the receiver what kind of loudspeakers you have so it can direct bass appropriately. Most of today’s receivers ask you whether each of the speakers is LARGE or SMALL (see Fig. 3 earlier). By selecting SMALL for the left and right speakers, you’re telling the receiver to keep low-bass signals out of those speakers. This configuration is used when you have a subwoofer connected to the system to reproduce low bass instead of the left and right speakers. You’ll also need to answer YES when asked if the system includes a subwoofer. The bass-management option labeled “THX” in THX-certified products automatically sets all speakers to SMALL and engages the subwoofer.

If your system includes full-range left and right speakers and no subwoofer, answer LARGE in the setup menu when asked if the left and right speakers are LARGE or SMALL. The LARGE setting directs bass to the left and right speakers.

The setup menu will also ask if the surround speakers are LARGE or SMALL. Nearly every installation will use the SMALL setting. Only if you have full-range, floor- standing speakers should you answer LARGE.

Although full-range left and right speakers deliver adequate bass extension and dynamics, you won’t hear the full bottom-end impact of today’s soundtracks without a subwoofer to reproduce the LFE channel (the LFE channel is the “.1” channel in 5.1- or 7.1-channel sound). That channel contains high-impact, low-bass sounds that can only be correctly reproduced by a dedicated subwoofer.

Selling Individual Channel Levels

Next you’ll need to individually set the loudness of each of the five channels (Six if you’re using a subwoofer), or seven channels (eight if you’re using a subwoofer) in a system equipped with Dolby Digital Plus and DTS-HD decoding. In addition to pro viding an overall volume control, all A/V receivers provide adjustment of the individual channel volumes. This process begins by turning on the “test signal,” a noise-like sound generated by the A/V receiver. (Dolby licensing requires that the receiver or controller incorporate this noise generator.) The noise is produced by each speaker in turn. Ideally, the noise signal’s volume should be the same for each speaker when you’re sitting at the listening/viewing position. If it isn’t, you can adjust the volume of each speaker independently using the receiver’s remote control. Individually adjusting the channels lets you compensate for different loudspeaker sensitivities, listening-room acoustics, and loudspeaker placements.

Although setting the individual-channel levels by ear will get your system in the ballpark, a more precise calibration can be achieved by using a Sound Pressure Level (SPL) meter. Available from RadioShack for about $30, an SPL meter lets you accurately calibrate your home-theater system. RadioShack offers digital and analog SPL meters; buy the easier-to-read analog type (catalog #33-2050). Switch the meter to the C-WEIGHTED O51t1Ofl, SLOW RESPONSE, and set the knob to 70. Turn on the test noise on your A/V receiver and set each channel’s volume until the meter’s display reads 5. This indicates that the noise is being reproduced at a level of 75dB. Repeat this procedure for each channel.

A powered subwoofer usually has a knob on its back panel for setting loudness. You should set this volume knob in a position that provides roughly the correct loudness so that you can fine-tune the volume through the receiver’s channel-level control. When you set the subwoofer’s level, the meter will be hard to read because the indicator will be jumping around (it’s reading a low frequency). Stare at the meter for a few minutes as it jumps to get an idea of where the average level is.

These settings will get you very close to the optimum volume for each channel, but you should use your ear and some well-recorded film soundtracks in making the final adjustment. If you find that dialogue is hard to hear, a 2dB boost in the center-channel level will help bring it out (although the soundstage will be focused more in the center than spread out across the front of the room). If the bass is thumpy and boomy, turn down the subwoofer. Don’t be afraid to make small adjustments to the volume of the subwoofer, center channel, or surround speakers.

Although your ears should be the final judge when setting the individual channel levels, calibrating your system first with the SPL meter (or by ear with the test noise) will at least get you started from the right place. The most common mistakes in setting channel levels are a subwoofer level set too high and too much volume from the surround speakers. The bass shouldn’t dominate the overall sound, but instead serve as the foundation for music and effects. Many listeners think the more bass you hear, the more “impressive” the sound. In reality, a constantly droning bass is fatiguing, and robs the soundtrack of impact and surprise when the filmmakers want you to hear bass. Low frequencies are used as punctuation in a film soundtrack; by keeping the subwoofer level appropriate, you’ll achieve a more accurate and satisfying sound than if the subwoofer is constantly droning away. Though it’s understandable that you paid for this big box in your living room and you want to hear what it does, try to avoid the temptation to set the subwoofer level too high.

Similarly, listeners who have never had surround speakers in their homes think they should be aware of the surround speakers at all times. In truth, film soundtracks don’t always contain signals in the surround channels; long stretches of the movie may have nothing in the surrounds. But even when a signal is driving the surround speakers, you should barely notice their presence. Remember, the surround channels provide a subtle ambience and envelopment. If you’re consciously aware of the surround speakers because they’re set too loud, the illusion they’re supposed to be creating is diminished. Just as it’s a temptation to set a subwoofer’s level too high, don’t turn up the surround speakers to the point where you hear them. Note that you won’t hear any sound from the surround speakers unless the source program has been Dolby- or DTS-encoded (unless you have Pro Logic or other processing engaged).

Adding Home Theater without Compromising Music Performance

Our job involves evaluating cutting-edge, state-of-the-art 2-channel audio products as well as high-performance home-theater components. Clearly, the performance of our 2-channel system cannot be compromised by the presence of home-theater products. Here’s what we’ve done to integrate home theater into our music-playback system.

First, our video display is a front-projection system with a retractable, motorized screen. The projector is at the back of the room, and when we listen to music, the screen is rolled up into a small enclosure. With the screen in the lowered position, soundstage depth is compromised, as is the precision of image placement. If you use a front projector, a motorized screen’s ability to retract for music listening is a big benefit. If you must use a fixed screen, drapes that can be drawn across the screen when you play music are effective at preventing the screen from reflecting sound.

Those who use a flat-panel television or rear-projector big-screen are faced with the challenge of having a large, acoustically reflective object near the loudspeakers. As described in Section 12, absorbing acoustic reflections at the loudspeaker-end of the room is important. To minimize the television’s degradation of the sound, move the television back as far as possible, and bring the left and right loudspeakers forward.

As mentioned earlier, an analog-bypass mode on a controller is absolutely essential if you want to listen to analog sources with the highest possible fidelity. This feature passes analog input signals through the controller without converting the signal to digital and then back to analog. Keep in mind, however, that even the very best multichannel controllers fall short of the performance standards set by high-end 2-channel preamplifiers, even in analog-bypass mode. If you want uncompromised musical performance, you’ll need a controller and a separate 2-channel pre-amplifier. The pre-amplifier should have a “theater pass-through” mode that sets one of the inputs at unity gain (the output signal’s amplitude is the same as the input signal). The left and right outputs from your controller drive this unity-gain input, and the preamplifier is connected to the power amplifier in the usual way. When watching movies, it’s as though your preamp isn’t there. When listening to music, it’s as though your controller isn’t there. With this technique, shown here, your analog sources never go through the controller. If you choose this option, you don’t need a controller with analog bypass, except on the multichannel input.

Addendum: Surround-Sound Formats

I’ve broken out a full explanation of the various surround-sound formats for those readers interested in more technical detail. Even if you’re not technically inclined, this section includes useful information about choosing among the vast array of decoding formats in today’s AVRs and controllers.

We’ve already covered Dolby Pro Logic, Dolby Digital, and DTS in the body of this section. Now let’s look at variations on those formats.

In mid-2001, Dolby Laboratories made available a more sophisticated version of Pro Logic decoding, called Pro Logic II. The idea behind Pro Logic II was to create from 2-channel sources a listening experience similar to that of a discrete 5.1-channel digital format. And with more consumers having 5.1 -channel playback available to them for reproducing music sources, Pro Logic II attempts to deliver multichannel sound from 2-channel recordings, even those that have not been surround-encoded.

Found on most A/V receivers and controllers made after early 2002, Pro Logic II offers improved performance over its predecessor in several areas. First, Pro Logic II delivers full-bandwidth stereo surround channels rather than the bandwidth- limited monaural surround channel of conventional Pro Logic decoding. This attribute provides a more enveloping soundfield, greater precision in the placement and pans (movements) of sounds behind the listener, and more natural timbre of sounds reproduced by the surround channels. In this respect, Pro Logic II emulates the experience of listening to a 5.1-channel discrete digital source.

Pro Logic II also uses more sophisticated “steering” circuits that monitor the level in each channel and selectively apply attenuation (reduction in level) to prevent sounds in one channel from leaking into another channel. Pro Logic IIx, announced in late 2003, creates 7.1-channel playback from 2-channel and 5.1-channel sources.

Not to be outdone, DTS has developed a suite of surround-decoding formats that either enhance the DTS experience or provide decoding of non-DTS sources such as conventional stereo.

DTS Neo:6 Music and Neo:6 Cinema are decoding algorithms that convert stereo or Dolby Surround encoded 2-channel sources into multichannel surround sound. Neo:6 Music leaves the front left and right channel signals unprocessed for the purest reproduction and extracts center and surround-channel signals from the 2-channel source. DTS recommends this mode for all 2-channel sources, such as CD and FM broadcasts.

Neo:6 Cinema is similar to Dolby Pro Logic II decoding, and can be used with Dolby Surround-encoded sources. Neo:6 Cinema has a much larger effect on the signal, rearranging the signal distribution among the front three channels. Both Neo:6 Music and Neo:6 Cinema create a 7.1-channel signal from 2-channel sources.

These decoding algorithms are very useful to those, like me, who greatly enjoy musical performances on DVD. When a DVD gives me the choice of listening to the Dolby Digital or 2-channel Surround-encoded linear pulse-code modulation (LPCM) mix, I always opt for the 2-channel mix. Although I lose all the advantages of Dolby Digital (complete channel separation, for example), I hear smoother treble, less grainy instrumental and vocal textures, and a greater sense of space. That’s because Dolby Digital uses 384,000 bits per second (or 448,000 bits per second) to encode all 5.1 channels; the linear PCM track uses 1.536 million bits per second to encode just two channels. When using Pro Logic II and DTS Neo:6 to decode these two channels, however, I still hear excellent spatial resolution, but with the more natural timbres made possible by the linear PCM track’s much higher bit rate.

In 2004, Dolby Labs and Lucasfilm jointly developed the Do/by Digital EX format. Dolby Digital EX encodes a third surround channel in the existing left and right surround channels in the Dolby Digital signal. This additional surround channel, called surround back, is decoded on playback, and the signal drives a loudspeaker (or two loudspeakers) located directly behind the listener. Dolby Digital EX allows film makers to more precisely position and pan (move) sounds around the room. For example, the sound of an object moving directly overhead from the front of the room to the back tends to become smeared; the sounds starts in the front speakers, then splits along the sidewalls as it moves toward the rear of the room. By adding a third surround channel directly behind the listener, these “flyovers” can be made more realistic. Note that an EX-encoded soundtrack is compatible with all Dolby Digital playback equipment because the addition of the surround-back channel is encoded into a conventional 5.1-channel Dolby Digital signal. Dolby Digital EX is not a 6.1-channel format; it is still 5.1-channels, but with the additional channel encoded within the 5.1-channel datastream.

DTS’ equivalent format is called DTS-ES. You’ll also see it called DTS-ES Matrix, because the additional surround channel is matrix-encoded into the existing left and right surround channels. DTS also offers DTS-ES Discrete, in which the surround-back channel is a discrete channel in the ES-Discrete bitstream. DTS-ES Discrete is a true 6.1-channel format. The advantage of a discrete format is complete separation between channels. Matrix surround systems have limited channel separation.

Note that Dolby Digital and DTS are “lossy” formats, meaning that some information is lost in the encoding and decoding process. This loss of information is intentional so that the number of bits required to represent the signal can be dramatically reduced. Consequently, Dolby Digital and DTS have reduced fidelity to the source.

The massive storage capacity of Hi) DVI) and Blu-ray Disc have allowed Dolby Laboratories and DTS to develop better-sounding surround-sound formats with higher bit rates than Dolby Digital and DTS. From Dolby Laboratories, we have two new formats called Do/by Digital Plus and Do/by TrueHD. Dolby Digital Plus is an extension of the conventional Dolby Digital we’ve been listening to for years on DVD and HD television shows. Dolby Digital Plus offers more channels and a higher bit rate for better sound quality. Where Dolby Digital was limited to a maximum bit rate of 640kbps (kilobits per second), Dolby Digital Plus allows scalable bit rates up to 3Mbps (million bits per second) on HD DVD and up to 6Mbps on Blu-ray. In addition to more bits per second, Dolby improved the encoding algorithms in Dolby Digital Plus for better sound.

For the ultimate in sound quality, Dolby has introduced Dolby TrueHD, which delivers high-resolution multichannel audio with perfect bit-for-bit accuracy to the source. With TrueHD, you will hear in your home sound quality identical to what the engineers heard in the studio. TrueHD decoding is an option, rather than a requirement, in HD DVD and Blu-ray players. The availability of a consumer release format that delivers uncompressed high-resolution multichannel audio is nothing short of a revolution in home entertainment.

With more than 40 million Dolby Digital decoders in use throughout the world, Dolby made sure the new formats were backward-compatible with your receiver or controller. The new players output a conventional Dolby Digital or DTS bitstream on the familiar coaxial or optical digital outputs for connection to your receiver. This output will likely sound a little better than Dolby Digital from DVD because it always operates at the highest possible data rate of 640kbps.

DTS has introduced its own high-resolution surround-sound audio format for HD DVD and Blu-ray called DTS-HD. This new format is an extension of conventional DTS, offering scalable bit rates from conventional DTS at 754kbps, all the way to 3Mbps on HD DVD and 6Mbps on Blu-ray. A variant of DTS-HD, called DTS HD Master Audio, can operate at higher bit rates (up to 18Mbps on HD DVD and 24Mbps on Blu-ray) for true lossless encoding of high-resolution multichannel audio. The “Master Audio” tag signifies lossless encoding. As with Dolby True HD, HD DVD players are not required to implement DTS-HD Master Audio; however, if a player encounters that format on a disc, it must at least deliver the DTS core audio stream (that is, good old standard DTS).

All HD DVD and Blu-ray Disc players are required to have Dolby Digital Plus and DTS-HD decoding. Unlike DVD, however, that required a Dolby Digital track on the disc, the new disc formats don’t require any specific format. That decision is left to the disc’s producers.