Surround Sound Formats Today
Despite the heavy emphasis on video over the past 15 years, the evolutions of home audio and video have actually taken nearly identical paths.
Looking back on the home A/V market in the mid 1990s the industry began a transition away from the VCR and its low-resolution video and Dolby Pro Logic audio technologies into the DVD optical disc format.
As everyone knows the DVD format offered consumers an improved picture with 480 lines of resolution and progressive deinterlacing options. It also offered a choice of audio formats that included standard PCM stereo, Pro Logic and discrete multichannel DTS and Dolby Digital.
As the decade of the 1990s drew to a close the video category moved onto high-definition (HD) video, while the audio market experimented with the higher resolution Super Audio CD (SACD) and DVD-Audio formats (DVD-A).
The A/V market has fully adopted HD in the form of the Blu-ray disc format, which has evolved into ultraHD 4K/2160p discs. Along with the HD 1080 picture quality of Blu-ray, the format also offers the lossless audio formats DTS-HD Master Audio and Dolby TrueHD. These formats matched the performance of their video counterparts by providing consumers uncompressed audio at levels up to 24-bit/192kHz for 5.1 and uncompressed audio for 7.1 systems.
Music and Electronics Industries Embrace Lossless Sound
Back before the Blu-ray format was established as a quality form of home entertainment, recording and mixing engineers and electronics manufacturers both quickly adopted the potential of lossless multichannel audio.
Now with consumers, recording engineers and CE manufacturers all supporting lossless audio, the technologies are almost taken for granted because they’ve been so widely accepted.
“Audio professionals have embraced DTS-HD Master Audio because it offers high-quality audio and is lossless. That means they don’t worry about what will happen to their recordings and final mixes, since DTS-HD MA delivers precisely what they created--bit for bit exact. Moving one step down the line, DTS tools are intuitive and easily accessible for professionals at any level,” says Fred Maher, audio testing & mixing/mastering specialist for DTS, Inc. “As far as consumer electronics manufacturers go, we estimate more than 100 million households or closer to 120 million worldwide have Blu-ray playback capability/DTS decoding inclusive of BD standalone, PS3 and PC BD. Additionally, all of the major manufacturers have implemented DTS-HD Master Audio technology in some of their AVR models and the PC industry has started to adopt the technology.”
On the pro side of the transition Maher explains that it took the engineering community some time to adapt to DTS-HD Master Audio’s full potential, but once those mixing professionals got acclimated to the technology it actually simplified their jobs. “DTS Digital Surround is our legacy codec [it is a lossless format]... the one that put us on the map. Some engineers used to monitor their mixes in real time, through DTS’s encode/decode hardware to make sure that what they were hearing was what the end user/listener would hear,” he says. “The new technology actually simplifies the process for those professionals as they no longer need to go through the additional step and expense of listening to the output with encode/decode hardware. Instead [they] can just listen.”
Sound Perspective from the Pros
Maher says that generally when looking at the differences between the lossy and lossless formats, the lower the bitrate is, the higher the potential there will be for a loss of quality.
“The most common issues related to lossy codecs are a loss of high end, a loss of transients or ‘punchiness,’ unstable imaging and so on,” he points out. “Can consumers hear it … yes, however most consumers don’t have the time or the means to do listening tests. Given the opportunity, I believe that consumers can tell the difference between lossy and lossless audio. Sometimes, consumers do hear it, but don’t realize that better options exist and try to compensate by turning up the volume.”
In a recording studio/engineering environment Maher says the greater capabilities of DTS-HD Master Audio and Blu-ray provide mixing engineers the freedom to place instruments, vocals and ambient effects where they want to provide listeners with a more immersive experience. Back during the turn of the new millennium when the DVD-A and SACD formats were first introduced, Maher says there was some market confusion with the differences between the formats and the lack of information concerning compatibility with various disc players. Today he points out there is no market confusion because Blu-ray players support the Blu-ray, DVD, CD and other legacy formats.
Maher admits the transition from multichannel to stereo does change the approach a mixing engineer will use, but engineers are experienced enough to maximize the quality of both two-channel and multichannel mixes.
“In the world of stereo you have to work very hard to carve out space for each and every instrument in a mix. In the case of rock or pop music, you have electric guitars, vocals and drums all fighting for power and clarity in what is essentially the same frequency range. You would achieve this by using lots of compression and EQ in an attempt to give each instrument its voice,” he explains. “Mixing in surround allows you to pull apart the knot with placement. I find myself using less compensatory EQ and compression, thereby increasing dynamic range and overall quality.”
Quantifying Lossy and Lossless Sound
Remembering the intricate details of today’s digital audio formats can overwhelm even the most dedicated audiophile. Maher notes the major points of each format can be explained in this manner:
- DTS Digital Surround refers to the original Coherent Acoustics specification that was first demonstrated in 1995. This specification allows 5.1 channels of audio to be encoded from 384kbps to 1.5Mbps. The two rates most popular were those on DVD: 754kbps and 1.509Mbps. DTS CDs also used this format, coding at a rate of 1.2348Mbps. This codec is the classic lossy type. Lossy codecs employ techniques to discard information, with perceptually less important or irrelevant information being discarded first.
- Lossless codecs produce an output that is mathematically identical to the input, but they require more data. While there is quality variability across different lossy codec families, at a basic level with these codecs the higher the bit rate the higher the quality, and on DVD, DTS with a potential rate of 1.5Mbps was the highest quality audio that was possible.
- DTS ES and DTS 96/24 were the first format extensions to be added to the core specification. These additions allow an additional discrete channel or the possibility of higher sampling rates. Both of these formats are fitted within the 1.5Mbps rate and both can be put on DVD making it the only codec capable of discrete 6.1 or 96kHz sampling on this format. DTS-HD takes the extension idea to the next level to allow higher bit rates, higher sampling rates, more channels and the possibility of lossless coding.
- DTS-HD MA allows lossless coding with higher sampling rates and more channels, but will have a variable data rate as this is the nature of a lossless codec. DTS-HD HR allows higher fixed data rates than the core along with higher sampling rates and more channels. On Blu-ray DTS-HD supports up to 7.1 channels but the codec itself is capable of much more.
- All DTS codecs support 24-bit resolution. The maximum data rate for DTS-HD MA on Blu-ray is 24.5Mbps and in this format the MA data stream always includes a core DTS Coherent Acoustics stream to make it backward compatible.
- The DTS-HD codec outside of Blu-ray can go to much higher rates and the channels can increase well beyond 7.1 although no commercial formats use this capability yet
About the Author
Robert Archer, Senior Editor, CE Pro
Bob is an audio enthusiast who has written about consumer electronics for various publications within Massachusetts before joining the staff of CE Pro in 2000. Bob is THX Level I certified, and he's also taken classes from the Imaging Science Foundation (ISF) and Home Acoustics Alliance (HAA). In addition, he's studied guitar and music theory at Sarrin Music Studios in Wakefield, Mass.