November 2001

The Technology of Surround Sound

OK, a show of hands: How many of you have written off multichannel music after having heard a not-so-impressive demo or two? Me too -- at first.

But I kept listening. I wonder how you or I would have felt had we heard the very first demonstration of CD? Could we have ever imagined the magnitude of improvement possible? And what about television? Would David Sarnoff or Peter Goldmark believe what they were seeing if they could witness the latest HDTV broadcast of a live sporting event?

OK, OK -- enough badgering. It should be obvious that I’m asking you to reconsider your current objections and use past technological advances to consider the future and its possibilities. Perhaps your grandparents never did buy that second TV because the first one they bought broke and they figured it would never get any better or more reliable. Heck, it might have been just a fad.

Your kids will probably listen to multichannel music when they grow up. Think about it. You could be hip, a man ahead of your time.

I’m not suggesting that you simply accept what is thrust upon you by the industry. On the contrary. As a music lover, I believe that we must be adamant now, so that what we have to listen to in the future fulfills its true promise. If the only folks listening to multichannel music are those who don't care about fidelity or the true intent of the artist, we are going to be in a lot of trouble. My local car-audio emporium is already advertising surround sound for the car. Do you really want to leave it to Detroit?

Delivery systems vs. formats vs. digital signal processing

Before we go any further, some basic terminology needs to be set forth and explained. There are several terms that are mistakenly used interchangeably, which confuses the issue when we discuss multichannel music and its forms.

Delivery system refers to the source component and its type. This could be an SACD player, a DVD-Audio player, a CD player, a multi-track digital recorder, a satellite receiver. It refers to the actual processing hardware type, and should not be confused with format. This gets tricky, for example, when we note that some SACDs can play on CD players -- without the benefits of the DSD recording technology, of course -- because those discs have a layer encoded like a CD. The software is a hybrid disc, but when played on a CD player, the delivery system is the CD player. When you play a regular CD on an SACD player, it is read just like any CD being played by a CD player. The only time an SACD or hybrid disc utilizes the SACD delivery system is when it is played on an SACD player that is reading it as an SACD.

Format as defined here is a recording’s coding/decoding system. It is true that you can’t always separate the delivery system from the format, such as the case with SACD and DSD (Direct Stream Digital), because both are a single product. Think more in terms of an SACD player as opposed to a multichannel DSD recording. A better example is Dolby Digital or DTS, because these formats can exist in multiple delivery systems. DTS is available via CD players or DVD-Video, for example. Dolby Digital can be found in DVD-V, as well as digital cable and satellite broadcasts. Formats can show up in any delivery system that can store them and release them properly.

To add even more to the endless terminology, we will define digital signal processing (DSP) as any type of manipulation of an audio signal, such as matrixed surround sound. For example: a hall simulation derived from a standard two-channel CD by means of a receiver's processing circuitry. Although some may scoff at this, the technology is improving here as well. The introduction of Dolby Pro Logic II is important because it can be used with existing two-channel CDs, creating a fairly convincing soundfield. Some hardware manufacturers have their own proprietary techniques for using DSP. Although most will admit that purpose-recorded discrete music is much purer from the audiophile perspective, DSP does have its place.

Speaker configurations

The primary formats for home theater, Dolby Digital and DTS, specify at least a 5.1 speaker configuration or some variant thereof (the addition of a rear-center channel, for example). Therefore, DTS-encoded CDs and DVDs will be compatible with this configuration. This is good news for those of you with DVD player-based home-theater systems who want to simply go out and buy some music designed to play back over your current system without changing or rearranging your speaker system.

There are variations to this, though. The six channels available in both DVD-A and multichannel SACD can be configured any way the recording engineer or artists choose. Variants include the use of side-effects speakers placed outside of the mains, which replace both the center channel and the LFE (subwoofer) channel. David Chesky, of Chesky Records, advocates this speaker configuration/recording technique. Tom Jung’s Sacred Feast SACD [DMP SACD 09] adds a height channel replacing the LFE channel. However, you can simply use five of the six channels and omit this if you aren’t equipped for it. What you are left with is five full-range channels, which essentially deletes the sixth channel altogether. These examples require a varying degree of flexibility on your part as the configurations could mean actually moving speakers, or in the case of the height channel, dedicating a speaker to this by permanently installing one on the ceiling. Not having one does not prohibit you from enjoying this type of disc, however.

You’ll note the manipulation of the sixth, or LFE channel, for differing purposes depending on the recording. Recording engineers differ on the relative value of this channel for music. As well, there has been a lack of bass-management functions for both early DVD-A and multichannel SACD. To the consumer, this translates to the inability to steer the bass from smaller speakers to a larger, more capable subwoofer. It was (and still is to some degree) recommended that larger, full-range speakers be used in all positions to properly produce all the recording has captured. Subsequent players, particularly multichannel SACD models by Sony, have basic bass-management functions built-in, although without the flexibility of many standalone processors used for home theater. It's very important to research your purchases so that you know you are capable of replaying the disc in a configuration that makes sense. If not, you may be relegated to a two-channel experience only.

Giant steps

At the end of the day, we have the opportunity to take two giant leaps forward and toward the goal of better music reproduction in the home. The promise of a higher-resolution format, and more importantly, multichannel recordings, will give us what’s next. Although it is possible to set up a system for all the possible configurations, it would be both inconvenient and cost-prohibitive for most consumers. We’re entering a time when a standard would be most helpful to those of us who simply want to get set up and start enjoying a new level of musical realism in the home. Since I have heard this reality, I’m chomping at the bit for it. We're not there yet, but we're tantalizingly close.

...Jeff Fritz
jeff@soundstage.com

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