Surround From Two Channels

Feb 1, 2011 9:00 AM, By Kevin Becka



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Taking the stereo image beyond its obvious boundaries has been in the engineer’s toolbox since the discovery of mechanically induced flanging in the ’60s and the introduction of hardware effects like the phase shifter and Eventide’s Harmonizer in the ’70s. Later, in the ’90s, QSound and Bedini entered the market with their 3-D sound-processing algorithms and the Bedini Audio Spectral Enhancer (BASE), which promised an enhanced listener experience for music and gaming.

In the current age where computers are fast, and portable devices for entertainment and gaming and communication are plentiful and cheap, the questions have changed. Can I create credible 5.1 effects from two speakers for critical listening in the home, at the studio or on headphones? What’s more, can I deliver real-time, high-quality surround to portable stereo devices like a laptop, pad, headphones, gaming console, smartphone and auto? As you’ll read below, the answers are all yes: The surround-from-stereo game is afoot.

Because of the popularity of portable formats and the recent upsurge in 3-D TV and movies, the stereo-to-multichannel toolset has grown exponentially. Being that manufacturers are designing these tools for different users (pros and consumers), listening venues and output platforms, the approaches are numerous. For instance, some methods are playback device–agnostic: Encoding is done entirely at the front end for listening on any device, no matter if they’re headphones or speakers large or small. Other methods call for DSP at the back end, meaning you need a specific chip-level encoder/decoder in your playback device, whether it’s portable or not. These are often input-agnostic, meaning any source can be upmixed on the spot into 5.1, whether stereo from iTunes, YouTube, MP3 or any other 2-channel source. Other systems call for encoding, then playback decoding to a specific device such as a headworn system. Some of these are not transferable outside the specific gear and are even sometimes specific to a single user. As you can see, the prospect of delivering surround from two speakers is getting pretty thick.

There’s no argument that Dolby and DTS have brought 5.1 audio for post, broadcast, music and gaming to literally millions of users across a broad range of devices. On the encoding side, Dolby’s professional product set includes DP563 Dolby Surround and Pro Logic II Encoder, which encodes discrete 4- or 5-channel surround mixes into Left total/Right total (Lt/Rt) stereo to be delivered over two channels on stationary and portable devices. In addition, Dolby Pro Logic IIx allows upmixing from stereo or surround 5.1/7.1 to 7.1 Height or 9.1 with the addition of front-height channels.

Dolby also has a range of products found mostly on consumer notebooks priced between $400 and $800. The latest chip-level software for this market is Dolby PC Entertainment V. 4, just released at CES in Las Vegas, which promises to deliver a cinematic surround experience on portable devices. Kevin Brennan, senior product marketing manager, PC Segment, explains how the Dolby codec works: “If the content is 5.1, it leaves the content alone and does all the other processing we do on that version. If it’s stereo content, it upmixes it to 5.1 and does the additional processing to the upmixed version.” The additional processing to which Brennan refers to improves the intelligibility of dialog, levels the volume and adds some equalization. Some of these parameters are user-adjustable. “We’ve spent a lot of time and effort providing a UI set that allows the user to quickly enable, disable and configure the software,” explains Brennan. “It is important to have some level of configurability because not all content is created equally.”

What about latency for picture or games? Brennan answers, “The technology uses the Intel High-Definition Audio System, which is a standard that Microsoft, Intel and Dolby created. Any audio stream opened within the PC gets processed through the same audio path. In terms of latency between video and audio, it doesn’t arise; it’s compensated for within the PC.”

DTS offers a range of products for surround upmixing, starting with the Neural Upmix plug-in (reviewed in Mix October 2010). “It was originally used in our real-time broadcast products, and we developed it into a plug-in after we discovered that it sounded fantastic,” says DTS pro audio manager Tom McAndrew. Neural Upmix is a Pro Tools and VST plug-in that gives you 5.1 from two channels or 7.1 from 5.1. The discrete multichannel output is then encoded for Blu-ray or broadcast. The process promises zero artifacts if it’s downmixed. “That’s been sort of a dirty secret of some competing upmixing products,” McAndrew explains. “When you play the mix back in a consumer environment where it has to be downmixed back to two channels, it can create some phase and volume funk. This product does not do that.”

For consumer devices, DTS offers DTS Neo and Neural modes for A/V receivers and DTS Premium Suites for PCs. The suite offers a host of features including surround virtualization, bass boost, and volume leveling and normalizing, all within the suite’s sub-processors. For instance, DTS Surround Sensation UltraPC boasts an excellent surround listening experience from two speakers or headphones, whether the original content is stereo or multichannel. DTS Connect combines DTS Neo: PC and DTS Interactive for surround upmixing and digital connection of the PC to the home theater system via a high-quality digital audio connection.

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