The next step in surround sound
My first “beyond 5.1″ experience was in January 2000 at the Alexis Park Hotel in Las Vegas. My colleague from the USC Immersive Audio Lab, Tomlinson Holman, was in the small room next door explaining why more channels are needed. This was followed by a demonstration of the world’s first 10.2 system to a few members of the press.
The world of sound had come a long way from the introduction of the first stereo LP in 1957. But in fact, with 10.2 we were moving back in time. It was in the late 30s that researchers at Bell Labs had looked into the question of how many loudspeakers are needed to reproduce a seamless, realistic sound scene. The answer at the time was discouraging: it turned out to be an infinite number–not exactly a high SAF (spouse approval factor) idea. Two channel stereo, however, was the only way to deliver sound to the consumer and it was limited by the LP groove that had two sides. Certainly better than mono, it didn’t come close to delivering an immersive experience.
The audio industry made great progress since 1957 and in the 1990’s we saw the introduction of 5.1 channel surround sound. Combined with the emergence of the DVD as the delivery medium, 5.1 surround became widely accepted in consumer homes because it created better sound immersion to match our growing video displays.
But since the 90s, the industry misdirected its focus to more esoteric endeavors: high sampling rates and higher bit depths for digital audio. While technically superior than the early digital formats found on CD in the early 80s, these developments did little to provide the consumer with a better experience. Human hearing limits for frequency range and dynamic range had already been met with 48 kHz sampling rates and 24 bit word lengths. Going to higher sampling rates simply filled up the discs with more data and required higher processing power to decode, but provided no audible improvement to the listener.
There have been attempts to push surround sound to more channels, but they were unfortunately not guided by proper acoustical, perceptual, or even logical approaches. 7.1 systems emerged by adding two more surrounds speakers in the location that makes the absolute smallest difference to the listener: directly behind them. Research in psychoacoustics tells us that human listeners are best at localization in the front hemisphere, cued by what we can see. Having more channels behind the listener than in front wastes resources and doesn’t go very far in providing a more immersive and enveloping soundstage.
To make an audible improvement in surround sound requires more Channels in the right locations. That’s what Tom was demonstrating at the Alexis Park during the 2000 CES. But not just any channels. They have to be placed in locations carefully crafted to produce the required cues that give us the impression of a wide, seamless, and enveloping soundstage.
Nine years later we are ready to go beyond 5.1 channels. Our company, Audyssey Labs just announced our latest technology, Audyssey DSX (Dynamic Surround Expansion). Drawing on our research in room acoustics and psychoacoustics we hope to extend an important dimension of sound…space.
Tags: DSX, surround sound
