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Surround Sound Suffers From Poor Presentation

Among my various adventures and misadventures at the Audio Engineering Society's 119th Convention last fall, I attended several events that involved surround sound. As I pondered it all on the way home and began to prepare for a largish public surround-sound presentation, I realized I had some serious concerns about what I had seen and heard. I'd like to share them with you, as they may have some impact on the effectiveness and salability of our surround production efforts.

BIG ROOMS

There were perhaps a dozen lecture halls set up by AES at the Javits Center in New York for the delivery of papers, panels, workshops and tutorials. These halls were all equipped with the usual media paraphernalia that we have come to know and love, including public announcement, video and other presentation aids. The rooms were spacious, all with seating capacity for a couple of hundred souls with sore feet. We will not concern ourselves here with the significant and generic acoustic limitations, including air-handling noise, leakage from adjacent spaces, etc.

The PA systems generally included full surround 5.1 playback capability, so that one could bring in a DTS, DVD or SACD recording and, in theory, have it played back as part of a lecture demonstration.

This happened, of course, in several sessions, and I found the quality of the surround playback was sufficiently poor enough to be useless in many cases.

Part of this, I am beginning to realize, was simply due to room and audience size. In stereo, we have a median plane. Happily, a fair number of attendees, if they were so inclined, could listen while situated along the median plane. In surround, however, there is only a sweet spot (or zone), which can handle perhaps a dozen listeners.

What this means is that, in fact, 5.1 surround music cannot be reasonably presented to a large group of people without some special strategies devoted to deploying arrays of speakers, complete with dedicated delays, etc. There is no way to successfully demonstrate or illustrate issues of envelopment, complex phantom images or other bits of surround production craft. After thinking about it for a while, my guess is that it is difficult to do successful 5.1 surround presentations in a room larger than about 40-by-40 feet to a group of more than about 20 listeners. (I know that we seem to do fine with movie theaters, but surround channels there are handled differently, and there is a specific set of evolved production traditions relating to audio and specific for that space.)

What bothered me more than issues pertaining to room and audience size was the poor quality of the actual surround sound (not the content). The loudspeakers being used were typical generic sound reinforcement speakers on stands, spread around the room in approximately correct positions (within, say, 15 feet). Said speakers had poor high-frequency power response and no attempts appear to have been made to establish and denote a viable "sweet zone" for listeners. Furthermore, low-frequency level and spectrum management sounded way off, possibly nonexistent.

The result, to my somewhat practiced ears, was that those of us in the audience could not reasonably audition the surround sound examples. Levels were wrong, timbres were wrong, envelopment (or lack thereof) was wrong and spaciousness was wrong.

To exacerbate this, there were often questions about channel assignments, so we became unsure of what we were hearing. It became clear that the reinforcement system operators had only a limited grasp of what was going on, and that channel assignments may have been scrambled. Further, attempts to illustrate downmixes to stereo led to even more questions about channel assignments. One stereo example had sound coming from behind me and to the right, even though I was sitting midway back and on the right. Hmmm.

BROADCAST RADIO

I was particularly interested to attend the Surround Sound for Digital Radio event about various strategies used to get surround sound shoehorned into radio broadcasting, including Neural Audio, AAC Plus, and MPEG Surround. What was fascinating was that two significant problems emerged.

The first is that, due to data transmission constraints, all the schemes appear to use some sort of "composite" transmission, which involves folding the discrete surround down into two compressed channels for transmission during the encode process and then decoding back to 5-channel surround at the receiver. This is conceptually similar, of course, to the analog "matrixing" schemes by Dolby Pro Logic and Circle Surround. Unfortunately, such techniques usually make some big assumptions about the content of the various channels. This is a big step backward from discrete 6-channel transmission to a very much compressed 2-channel transmission that may not represent what the producer intended.

The second problem is due to us music mixers. We do separate stereo and surround mixes for separate release formats. Those separate mixes may be completely different arrangements, and may even be of different lengths. Naturally, we prefer that stereo broadcast should be of the stereo mix (not a downmixed surround mix).

We have abdicated our responsibility for stereo and mono compatibility, where one surround mix fits all broadcast formats. Meanwhile, the IBOC terrestrial broadcast system requires that the transmitted signal morph back and forth between the digital and the analog signal as needed. Well, with a separate "creative" stereo mix going out in analog stereo, that is not going to work!

The result of all this is not a pretty sound stage. From what little I could hear, the surround broadcast examples sounded terrible. By "terrible," I mean that I would not like my work to be presented this way, to a point where I would forbid it if I were given the option! Compression artifacts were gross, and there was little if any coherence to the overall mixes I heard, much less any compelling sensory quality or excitement.

Why should you TV types care? You've got Dolby E and Dolby Digital and you've got it all sussed out, right?

You should care because A) radio broadcast is going to be a major part of surround distribution in the near future, and if it sounds the way it did at AES, it is going to drive off a heap o' listeners, and B) not even well-meaning and technically qualified folks such as those in the Audio Engineering Society seem to be able to actually set up and viably demonstrate the medium reliably, due to its variability and complexity. As I've noted before on these pages, if we can't do it, Joey and Janie Six-Pack certainly aren't gonna be able to manage it either.

At it's best, surround sound is a phenomenal audio playback medium. It's hard (almost impossible, really) to go back to stereo once you've heard it in a fully developed setup. However, we are still a long way from there; we've still got a lot of improving to do.

Thanks for listening.