The World's Longest Continuous Musical Composition?

There are a variety of ways to empty a large bucket of water: The entire contents can be quickly dumped in a dramatic rush, or a small hole can be punched in the bottom, allowing a smaller but continual flow over an extended period of time. Digital data can be seen as the water in the DVD "bucket," with 24/192 multi-channel sound being the equivalent of a big audio splash.

Composer Robert Rich has decided to use the 4.7GBytes of storage allowed by the DVD format to create the equivalent of a steady seven-hour audio flow, instead. Possibly the longest continuous musical composition ever released on any format, Rich's latest ambient work, Somnium, represents a landmark in the history of recorded music.

The music for Somnium was a result of Rich's desire to release a studio version of his notorious all-night "Sleep Concerts," which have been performed live around the world for the last several years. He recorded the music for the new disc over a six-year period, starting with field recordings using the 16-bit, 48KHz format. As Rich describes it, "I would have preferred a 24-bit recording, but in this case I was limited both by the recording medium and the carrying medium. DVD simply cannot hold seven hours of 24-bit audio without compression, and the artifacts of AC3 compression are worse than the sound of 16-bit encoding.

"A wide dynamic range was not required with this recording, since it needs to keep an even enough volume to stay audible at very low overall levels. On the other hand, high resolution and imaging detail are essential to re-create the soundstage and wide ambience. I mixed the music so that it can hover at the threshold of one's attention during the night, without calling attention to itself. I wanted the sonic texture to be interesting enough to reward close attention. These goals sound contrary, but I found that they could be resolved by mixing the music while monitoring at normal listening levels, then mastering it while monitoring at very low volumes to make sure that the dynamics remained even. At low volumes, midrange frequencies will appear to predominate in a mix, so careful mixing and judicious EQ help to preserve the desired tonal balance when quiet. The mix has a more extreme 'smiley curve' than would have been appropriate for louder listening levels."

For field recordings, Rich used a Benchmark portable mic preamp, with a Sony TCD-D7 DAT machine and a selection of microphones including a Crown SASS-P binaural mic, a spaced pair of omni Neumann KM130s, and a near-coincident cardoid AKG 451. Rich says that he would use the Crown in high risk situations, such as the time he hung it over a cliff in Big Sur to capture some sloshing waves in a cove 30 feet below. "My main fear was that the weight of the microphone and cables would pull the preamp and DAT over the edge with it, although I probably should have been worrying more about my own safety, as half of my torso was leaning out over the cliff to keep the microphone from hitting the rocks as I lowered it down onto a shelf above the waves."

One of the more interesting recordings for Somnium took place in a lab at Scripps Oceanographic Institute, where an acquaintance of Rich's was studying a species of tropical fish that creates audio frequency electrical oscillations from its skin. "We placed about 16 fish in a bucket with three differential electrodes (positive, negative, and reference) plugged into a battery-powered Grass medical preamp designed for EEG. With the output of the preamp plugged directly into the portable DAT, we recorded a cloud of slowly shifting drones. Each fish emits a unique frequency as a sort of territorial marker, and as the fish lazily circulate around the bucket, individual tones become louder or softer in a very nonhuman slow-motion symphony."

Rich says that the DVD authoring process itself held numerous unpleasant surprises. "Nobody had tried putting such a long continuous track on a disk before. We learned that neither the authoring software nor the DVD itself could handle a single file larger than about 2GBytes, even though the medium could hold 4.7 Gig. Furthermore, DVD players require a certain amount of file size overhead that limits the practical maximum to about 4.3 Gig."

Other complications included finding ways to enable easy navigation for such a long recording. "If you wish to navigate or fast forward through the audio you need to add a frame of video to each frame of audio, which basically cuts in half your maximum audio file duration," says Rich. "In other words, after carefully editing the music so that it would fill the maximum duration that a DVD could hold, I learned it wouldn't fit.

"The authoring house gave me two choices: either AC3 encode the audio or omit the navigation. They sent me a sample with the mildest 2:1 AC3 encoding, but the compression destroyed the high-frequency spatial detail, and it made the midrange sound congested and lumpy. I decided to sacrifice the navigation so I could use straight PCM files. The audio still wouldn't quite fit because of the extra file overhead, so I selected a region in the middle of the piece that survived the AC3 encoding better than the rest, and we compressed that middle region. In any case, we needed to separate the audio into three regions because of the 2 Gig file size limitation. Unfortunately, many DVD players will briefly mute their audio playback when they encounter the two file boundaries in the middle of the piece, so we had to select two very quiet moments in an otherwise continuous piece of music so that the mutes would not be too noticeable."

More information about Somnium, along with Rich's list of listening tips, can be found at the composer's website at www.amoeba.com.

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