Circle Surround® 5-2-5™ Applications Notes No. 1
Circle Surround Playback Compatibility by Henry J. Root
INTRODUCTION
Four different issues will be explored as we look into the issue of Circle Surround playback
compatibility:
1] Playback of stereo recordings in Circle Surround
2] Playback of monophonic programming in Circle Surround.
3] Circle Surround playback of programming encoded with other algorithms.
4] Playback of programming encoded with other algorithms in Circle Surround.
Compatible, adj 1. capable of existing together in harmony; such as to agree; consist;
congruous, 2.
Denoting a System of television in which colour broadcasts can be received on
black-and-white television sets. 2
HISTORY
There are two basic types of matrix surround sound systems. As an outgrowth of one of the
quadraphonic Systems of the late 1960's, Peter Scheiber and David Hafler (in separate
work) turned the two speakers in front and two speaker behind box into a diamond. David
Hafler dematrixed stereo music passively. There wasn't much channel separation, but it was
musical.
Peter Scheiber flattened the front a little and created the idea for the home theatre speaker
arrangement. He employed active matrix 4-2-4 encoding and decoding and patented the
process. Dolby Laboratories licensed the Scheiber patents and called their technology
Dolby Stereo. The Circle Surround® 1 5-2-5 System has taken the classic matrix surround
process from its grounding in the early 70s and brought it into the late 90s while retaining
backward compatibility to all of the 4-2-4 matrix Systems.
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.
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: http://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.
1
Circle Surround is a registered trademark of Rocktron Corporation.
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