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about surround technology |
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about surround technology |
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Circle Surround® 5-2-5TM Applications Notes No.1
Circle Surround Playback STEREOPHONIC RECORDINGS REPRODUCTION If we apply the above definition to surround sound playback, we can say that a recording played back on a surround sound system is compatible with that system if all of the music recorded is heard by the listener. That is not to say that the music is heard in the same way it was by the audience at a Concert- if the recording was of a concert. It is to say that all of the music is represented in the playback. lf that is true then we can say the recording and the Circle Surround playback are compatible. That is not saying each of several different matrix systems would sound the same. If a non-encoded two-channel stereo recording were reproduced on a two-channel stereo playback system with high quality, full bandwidth speakers and with amplifiers of sufficient power, the music would sound a certain way. If that same recording were reproduced on a Circle Surround 5-2-5 System, it would sound different. There would be three frontal speakers to reproduce the Left, Center and Right channels, and there would be Left and Right Surround information dematrixed from the original two-channel recording. ...since the [C.S] matrix is completely stereo-compatible and indeed is said to enhance ordinary playback, it s entirely possible to sell the recordings as ordinary two-channel software, which is exactly what has happened in many cases. 3 The steering of the surrounds in the Music Mode was quite seamless, and with suitable source material, a very believable, and all-encompassing, soundstage was produced. 4 The number one design criterion in the development of the Circle Surround system was and is compatibility with stereo and with programming encoded with other (4-2-4) systems. lf the same recording ware reproduced through a ProLogic®5 decoder, it would sound different from the Circle Surround reproduction. (Dolby®) Matrix decoders, by their very nature, are not music friendly. The presence of vocal material pushes the matrix steering towards center-channel, and if your understand how the matrix decoder works, this means that left and right go mono. So while one may hear music effects move around us, the predominant musical listening experience through a matrix decoder is vocal in center and everything else in boring old mono on left and right. 6 Recording engineers should also be concerned with what is actually heard on playback and monitor their recordings in surround. Most engineers and producers don't do this, and they don't know how their recording will reproduce in this rapidly expanding technology nor where certain instruments may show up in the mix. MONOPHONIC RECORDING REPRODUCTION lf either of the above mentioned surround systems would be used for the playback of a monophonic program, the signal would be reproduced only from the center speaker. In very basic terms, the center channel is L+R, and L+R = Mono. The signal will come only from the center speaker. [back top...] CIRCLE SURROUND REPRODUCTION OF OTHER MATRIX RECORDINGS A number of matrix surround sound systems are on the market around the world that claim to have stereo surround channels. These will not be investigated here. Most manufacturers of such systems have white papers explaining the theory and operation of their own system. lf you are interested in delving into the theories and math involved, get in contact directly with the company whose system you are interested in. The Circle Surround 5-2-5 White Paper is on our website: [visit www.rsptech.com] The Circle Surround 5-2-5 Decoder has both a Music Mode and a Video Mode. The Music Mode was perfected first, and it has no steering or time delay. The panning and instrument locations created in the stereo mix are retained across the three frontal channels. The L-R difference information received location clues from the Left and Right channels for the Left and Right Surround channels. A delay is not required due to the total cancellation of the front signals from the surrounds. The Hass Effect is not needed as a crutch to force the listeners attention to the front. In the Video Mode the 5-2-5 matrix will offer stereo imaging even with a dominant center channel signal, such as strong dialog. This is very important since a large portion of any video/cinema production will have strong center dialog. The 5-2-5 system will offer greater separation for hard left or right surround to the front channels-better total channel separation. Programming encoded in the Dolby 4-2-4 matrix format and reproduced in Circle Surround will provide a greater left and right surround dominance. In some scenes a dominant surround pan will produce a dramatic left or right surround impact as in the movies Casper and True Lies where C.S. reproduced pans follow very closely the pans heard from the soundtracks on the DTS® 7 and AC-3® laserdiscs. When the 5.1 channel mixes are converted to 4-2-4, subtle cues are left in the matrix recording; these are detected by C.S. decoder which increases to steering sensitivity when there is dominant surround information and places the effect in the proper surround channel. The RSP (Circle Surround, ed.) Video Mode stands up very well and in some ways may have been subjectively better - particularly in the way it managed to maintain a wide frontal soundstage to the music and effects under dialog. . . . it is very creditable indeed and appeared to be entirely compatible. It effectively demonstrated the system s ability to place sounds precisely, anywhere in a 360° degree circle with complete imaging between any two speaker pairs including the left and right rears! ...With this level of spatial accuracy and freedom from coloration available from a matrix device, it brings into question the need for discrete multi-channel systems, especially those that require substantial data reduction. ...I think that the Circle Surround 5-2-5 sets new standards for accuracy in surround sound reproduction. 4-2-4 DECODING OF CIRCLE SURROUND ENCODED PROGRAMMING Programs encoded using the Circle Surround 5-2-5 matrix will playback compatibly on any of the matrix decoders available today. Obviously, the full bandwidth stereo surround signals encoded using the 5-2-5 format will not be enjoyed when using a 4-2-4 decoder with it's restricted bandwidth monophonic surround channel. The image collapse of the front soundstage pointed out by Michael Karagosian will still occur since it is a deficiency of the musically unfriendly 4-2-4 matrix algorithm and its always dominant center channel. While the double d matrix has set a standard, of sorts, in the over twenty years since it's commercial release, it is not, nor was it ever, intended for music listening. Several companies are offering other iterations of the basic Scheiber matrix that are not compatible. Careful listening is required. [back top...] 2 The American College Dictionary p1959 Random House, Inc. 3 A new Kind of Channel Surfing by Daniel Sweeney in Home Theatre, March, 1997. 4 RSP Technologies Circle Surround System by Hugh Robjohns, BBC Lecturer at Center for Broadcast Skills in Audio Media October, 1996 5 Dolby, AC-3 and Prologic are registered trademarks of Dolby Licensing Corporation. 6 Michael Karagosian, President, Cinema Group Ltd. In Pro Sound News, 16 March, 1997 7 DTS is a registered trademark of DTS Technology. 8 Circle Surround 5-2-5 an equipment review by Richard Hardeaty in Wide Screen Review, issue 20 [back top...] CIRCLESURROUND® 5-2-5TM APPLIKATION NOTES NO.2 DVD 5.1 Channel Playback using a Circle Surround 5-2-5 Decoder by Henry J.Root From the Behind the Scenes section in the Fall, 1997, issue of Stereophile Guide to Home Theatre®, Technical Editor Thomas J. Norton cleared away a lot of unanswered questions and misinformation that has been fostered in other publications in the following excerpt in which he admonishes us to Read the Fine Print: DVD and AC-3. "Early adopters of the new DVD format are about to discover-if they haven't already - that not all DVD titles contain discrete 5.1 channel Dolby Digital® soundtracks. Instead, some discs have good old-fashioned matrixed Dolby Surround mixes, which must be decoded by Dolby ProLogic (or Circle Surround®, ed.) circuitry for users wanting surround-sound playback. A few titles will even be monophonic. "What's that?" You thought all DVDs sold in North America had soundtracks encoded using Dolby's AC-3 data-compression algorithm? Well, you're right-they do. We've become so accustomed to thinking Dolby Digital (AC-3) as a discrete 5.1 channel format that we forget AC-3 may be used to encode any number of channels (with or without matrix surround information). Or even one. "Why would anyone use Dolby Digital (AC-3) data compression to put plain-Jane, two-channel matrixed Dolby Surround, or even mono, on a DVD? Because ordinary PCM digital - the non-compressed audio format you get with CDs and the conventional digital audio tracks on laserdiscs - would use approximately 15 percent of the available data space on a DVD alone-never mind multiple languages. And that's too much. Two-channel, uncompressed PCM audio tracks could be used on DVD for shorter programs such as music videos, but it's highly unlikely that you II see anything but data-compressed audio tracks - Dolby Digital and perhaps DTS® in the U.S. and MPEG in Europe-on movie DVDs where data space is critical. So we now have two AC-3 encoded tracks carrying matrixed Dolby Surround information (ignoring, the time being, the mono option). To play these tracks back, they must first be AC-3 decoded, then routed through a ProLogic (matrix, ed.) decoder to derive the matrix surround. For most users, this will not be a problem; all DVD players can decode two channels of AC-3 and perform the D/A conversion needed to produce the required left and right channel (LT/RT, ed.) analog outputs. Hook up these outputs to any ProLogic (or other matrix, ed.) processor and you're in business for surround (or stereo or mono) DVD playback. To play back DVDs having full 5.1 channel Dolby Digital tracks, you use a separate digital feed from the DVD player to the Dolby Digital processor. "Using the DVD players analog outputs for everything except 5.1 channel Dolby Digital will, however, restrict the quality of ProLogic (matrix, ed.) Or mono replay to that permitted by the DVD players on board, two-channel AC-3 decoder and D/A converters. Some high-end surround processors (such as Denon AVP-8000 and the Theta Casablanca) avoid this limitation by accepting the DVD players digital output for all types of DVD soundtracks. These processors automatically (or via a user-control switch) accommodate whatever format is camed by the Dolby Digital data-stream, be it discrete 5.1, matrixed Dolby Surround, or mono. "Though we've just begun our serious evaluation of the DVD format, the first batch of titles we received from Warner® is an interesting mix of the above possibilities. If you look at the fine print on the bottom rear of a DVD box, you II see what amounts to a thinly disguised code in probably the smallest legible typeface Wrner could find." Dolby Surround 5.1 = discrete surround Dolby Surround Stereo = matrix surround Dolby Digital = mono [All DVDs can be decoded through a Circle Surround decoder. Ed.] One word of reassurance for those without 5.1 channel Dolby Digital replay equipment: aside from any two-channel Dolby Surround mixes that may be recorded on DVD and are handles as discussed above, all current players can also internally process the 5.1 channel tracks, when present, to reduce them to two-channel (LT/RT) Dolby Surround (matrix, ed.) mix. This mix is then decoded (it s still in AC-3 form), converted to analog, and routed to the player s analog outputs. These two analog output channels may then be fed to your matrix surround processor and converted for replay in the same manner as any matrixed material. A number of listening tests have been performed comparing the Circle Surround 5-2-5 matrix decoder (in Video Mode) against the 5.1 channel discrete digital decoders. The worst result was a draw using a DVD during a shoot-em-up segment of Eraser. All other segments of movies compared, using both DVDs and laserdiscs, the Circle Surround 5-2-5 decoder was the clear preference. There was no contest involving music sources. The Circle Surround 5-2-5 Music Mode did maintain the same frontal imaging contained in two-channel stereo recording, but the listeners heard a hard center channel (without the image collapsing into the mono) and the full bandwidth, stereo surround channels reproducing the non-coherent ambience contained in the music. Using encoded music, it is possible to hear true stereo from the surround Left and Right channels. Both modes produced a sonic environment that enveloped the listeners with sound that even made converts of hardcore stereophiles. The lack of image wandering caused by the dedicated dominant center channel of all 4-2-4 systems was a real attention grabber. Even though some listeners couldn't verbalize what they heard, they all agreed on the superiority of the Circle Surround 5-2-5 technology. Richard Hardesty in review of the Circle Surround technology in Wide Screen Review wrote, with this level of spatial accuracy and freedom from coloration available from a matrix device, it brings into question the need for discrete multi-channel systems, especially those that require substantial data reduction. . . It effectively demonstrated the system s ability to place sound precisely, anywhere in a 380° degree circle with complete imaging between any two-speaker pairs including the left and right rears. [back top...] |
