Surrounded by gray, tangled up in blue
By Brian Dipert, Technical Editor -- EDN, January 9, 2003
My last EDN editorial proposed that, whether in engineering or in the broader subject of life, little to nothing is completely right or completely wrong, completely true or completely false. I've thought a lot about the "gray zone" in recent months, first while at the Audio Engineering Society Conference in Los Angeles last fall and subsequently while researching this issue's cover story on high-resolution audio. If you read it, you will, I hope, infer my opinion that the biggest chance for success for any of the new audio formats comes from their surround-sound characteristics—not from their high sample rates or large sample sizes. And, from the title of this editorial, you might also correctly interpret that I'm looking forward to listening to surround-sound remasters of the Bob Dylan archives!
Many audio purists completely reject the idea of surround sound and, for that matter, digital audio of any sort, in favor of their beloved LPs. Audiophiles open to the idea of surround sound often insist that the record labels completely remix the DTS audio CDs, DVD-Audio discs and SACDs (Super Audio Compact Discs) from the original multitrack recordings. But in the spirit of the gray zone, is this situation really just an all-or-nothing proposition? Or do intermediary approaches also deserve consideration? What if, for example, the original tracks no longer exist or they've degraded (due to age, perhaps accelerated by an imperfect storage environment) so badly that baking won't even temporarily restore them, and the oxide would fall off the tape if you tried to play it? In this case, the producer in charge of the remastering project will have to derive a surround-sound variant using only the monophonic or two-channel master. And, even if the original tracks are available, is a painstakingly slow, expensive, fully manual remix necessary, or could a computer-assisted approach more quickly and cost-effectively deliver comparable-quality results?
"Time to market" isn't just an engineering term, after all. Consider, for example, SRS Labs' Circle Surround Repurposing Tool, which transforms conventional audio into a surround mix with as many as 6.1 channels. For several years, I had a Sherwood Labs Circle Surround decoder that also supported DTS in my car, and I therefore speak from experience when I tell you that it did an amazing job of transforming mono- and two-channel audio CDs into an immersive surround presentation—far more realistic than a conventional dual left- and right-channel arrangement. This situation was true even though my car had no center speaker, and the decoder, therefore, also had to create a phantom center image. Simply stated, Circle Surround works by extracting and exaggerating left-versus-right-channel differences and shifting them toward the rear channels, redirecting information common to the left and right channels to a center channel, and employing a lowpass filter to the source audio for subsequent redirection to a subwoofer channel. The company declines to reveal the theory behind its mono-to-multichannel-transformation algorithms, but filter-band allocation is a common technique for accomplishing this objective. SRS Labs' algorithms don't necessarily create a surround mix that puts you in the middle of the band, but its rear-channel-echo and reverb effects generate an often equally acceptable perception that you're in the audience listening to the band, a perception that is exactly your objective for a live recording.
What if you really want to have Miles Davis' trumpet blasting away from behind the listener's right ear, Stevie Ray Vaughan's guitar behind and to the left, David Lee Roth's vocals heading to a spot directly between the eyes, or John Bonham's drum set swirling around the listener at 60 rpm? Mixlab has created an algorithm that not only extracts phase information, but also comprehends the various instruments in the mix and, at any point in time, whether they're playing a primary or supporting role. Mixlab then suggests where the recording engineer might want to place each extracted instrument track within a 200×200-point matrix surrounding the listener. Sounds like science fiction, until you discover that Trey Anastasio, the talented and perfectionist lead guitarist and vocalist in Phish, relied on Mixlab to create the DVD-audio of his recent solo album, a DVD-audio disc that sounds incredible.
There's a strong temptation to perpetually keep doing things the way you have always done them and to give up on engineering challenges that perpetual-motion methods can't solve. Keeping your eyes and ears open for the latest technological developments, though, and always being open to incorporating those developments in your bag of tricks, will keep your engineering career fresh and elevate you to hero status among your bosses and peers. Last time, I encouraged you to nimbly go with the flow and revel in the excitement of the unknown. I look forward to hearing your success stories.
Contact me at bdipert@edn.com.
