Five Boys and the Man

5.1 Audio

I would call 5.1 audio as being the tidemark in the evolution of multichannel audio. It was during this time that the source signal became digital. The source signal now contained separate channels for all the speakers including the subwoofer. The frequency response of the rear channels were upgraded to full frequency without any limitations. Subwoofers received their own LFE or Low Frequency Effects channel that was designed to help you feel the music, literally. Pioneering this signal source was Dolby Digital.

Dolby Digital is commonplace now with Xbox and most DVDs supporting it. In the beginning, it was only available on Laserdiscs and was often called AC-3 audio. Some argue that AC-3 Dolby Digital is superior to DVD Dolby Digital because the Laserdisc used no compression on the front channels. Dolby Digital is a lossy compressed digital audio format. Some purists would argue that any compression is detrimental to the fidelity of the signal. What I think you should be interested in is the perceptibility of this fidelity. For the most part, the compression of Dolby Digital is good enough.

Enter the DTS

Not everyone agreed about that last point and DTS came out with their own 5.1 signal carrier. The setup is the same as Dolby Digital. The major differences are that DTS uses less aggressive compression and can be carried on a standard PCM data bus. This last point enabled DTS to be used on any machine with an optical PCM output. Old laserdisc players could support DTS, DTS could be recorded on standard redbook CD audio format. On paper, DTS looks more practical and technically superior with less compression, yet it is well overshadowed by Dolby in terms of market penetration. One of the main reasons for this is that DTS in being less compressed, takes more storage space, limiting the number of extras that can be crammed on a DVD. Some would argue that DTS hasn’t taken over because most purchasers of DVDs can’t hear a difference.

Hearing a difference is harder than it initially appears because the DTS and Dolby Digital tracks on the same DVD often have different mixes, so you are listening to not just different compression algorithms, but different mixes. That said, when going head to head with identical material, DTS does sound better.

DTS can also be found on music CDs and some car audio units. The packaging of DTS in PCM format enables this diversity.

This 5.1 format was very stable for many years, with a few companies making unique tweaks on the format. THX added their decorrelation on cinema re-equalization as well, and receiver makers all had their own DSPs that used the 5.1 data and extrapolated it to the 5.1 speakers or more.

New standards

More recently, standards have come out to take two channel sources into 5.1 channel outputs. Dolby Pro-Logic II and DTS Neo-6 are the most popular of these algorithms, with individual manufactures developing their own such as Circle Surround or Logic 7. These additions really give new life to your stereo signal.

For music only fans, 5.1 music is available by using DTS music cd’s, Super Audio CD’s, or DVD Audio. DTS music cd’s are recorded in PCM redbook and can be played on a variety of players that interface through a digital cable to your decoder. Super Audio CD and DVD Audio require specialized players and most can only output the six channels to your amp through an analog connection. The reason for this is that most receivers do not have the ability to decode these signals and the music industry doesn’t want people transferring such high fidelity sources digitally.

Higher resolution

Super Audio CD was Sony and Philips’ love child, and has the backing of major music labels. They also make hybrid discs that are readable by standard CD players, but at the standard CD resolution. Regular CD’s sample sound at a rate of 44.1khz at 16bits of resolution, Super Audio CD does it at 2.8224Mhz at 1 bit, nearly an increase of an order of magnitude. DVD Audio samples at 192khz at 24bits of resolution. Both these new format extend the recording frequency response to over 100khz compared to 20khz for standard CDs. While bats and dogs are sensitive to sounds above 20khz, people are not. The thought is, however, that interactions between these ultrasonic sounds can be audible. Whatever the explanation, SACD and DVD Audio do sound better than standard CDs, not just for their discrete multichannel format, but also for their improvements in resolution and imaging.