Lexicon CP-3 Plus Supplementary Manual
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Lexicon CP-3 Plus Supplementary Manual

Lexicon CP-3 Plus Supplementary Manual

Digital surround processor theory and design
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  • Page 1 PLUS CP-3 Theory Design...
  • Page 2 Copyright ©1991, 1995 Lexicon. Inc. All Rights Reserved. Lexicon Patent: U.S. no. 4, 862, 502; other patents pending on the CP-3. Lexicon, Inc.• 3 Oak Park • Bedford, MA 01730 USA • Tel 781-280-0390 • Fax 781-280-0490 Lexicon Part #070-08806 Rev 2 Lexicon...
  • Page 3 Lexicon The CP-3 PLUS Digital Surround Processor Expanded Remote Standard Remote Front Panel Rear Panel...

  • Page 4: Theory And Design

    Unfortunately, our listening rooms do not approximate the acoustics of a good concert hall, an intimate jazz club, or a magnificent cathedral — our ears tell us where we really are. The Lexicon CP-3 overcome this fundamental limitation to two-speaker reproduction and bring us closer to the ultimate goal of transporting ourselves to the original musical event.
  • Page 5 The requirements for processing sound for home theater are quite different than those for music. Lexicon invented the technology that permits the most accurate reproduction of film sound in the same system that is used for music listening, and the software-based CP-3 these unique tasks.
  • Page 6 PLUS CP-3 Digital Surround Processor Concert Hall Acoustics For decades the study of concert-hall acoustics relied on certain basic measurements to characterize halls, the main one being the time it takes a sound to drop in level (decay) by 60 decibels. This is called the reverberation time or RT and is approximately the same as the time it takes a hand clap to subside to inaudibility.
  • Page 7 (with curtains or sound-absorbent panels). When this is done the room becomes quieter and clearer but not in any way like the original hall. The Lexicon CP-3 PLUS resolves this deficiency by supplying appropriate signals to loudspeakers at the sides of the listener or by modifying signals...
  • Page 8 PLUS CP-3 Digital Surround Processor at the sides. Both methods depend on having the added sound come from a different direction than the original music, and each method has some advantages. With either method of generating SI there is an additional choice the CP-3 PLUS allows the user to make: the sideways energy cues of the...
  • Page 9 Furthermore, the listener’s head is not well represented by a simple delay line. Both the delay and the amplitude of the opposite-ear sound vary in complicated ways with fre- quency. Lexicon PLUS uses crosstalk...
  • Page 10 CP-3 PLUS Digital Surround Processor Lexicon’s implementation, called the Panorama mode, was designed using measured data on sound diffraction around the head to shape the frequency spectrum of the canceling signal. This signal is then itself canceled by a second signal, and so on, so that both the crosstalk and the signal that is canceling it are eliminated.
  • Page 11 Panorama Wide. Negative values of the Low Frequency Width parameter can bring the low frequencies back in line with the higher frequencies and make the playback with Panorama more effective. The Binaural setting of Lexicon PLUS . First, there are the three...
  • Page 12 The reflections were determined by computer ray-tracing using architectural data, augmented by Lexicon’s decades of experience with digital concert-hall simulation. The Ambience simulation is done in stereo. Instead of feeding a monaural...
  • Page 13 Liveness parameter), for long decay times it is better to use Reverb. The Large Hall ambiences are not intended to be used on material which is more appropriate to a smaller ambience, such as a small hall or a club. Lexicon PLUS using the Ambience mode: Try the...
  • Page 14 CP-3 PLUS Digital Surround Processor Highly percussive material is almost always better in the Small mode which is quite successful in livening and expanding popular music. If you have no side loudspeakers, both Ambience and Reverb contain versions of the Panorama mode that will simulate them within a narrow area between the speakers.
  • Page 15 THX CINEMA combines Dolby Pro Logic decoding and the spectral en- hancements of the LucasArts Home THX Cinema system to recreate film sound in your home the way it was heard in the final production stages. In the CP-3 a further enhancement, Stereo Surround, is also available. PLUS Lexicon...
  • Page 16 PLUS CP-3 Theory and Design PLUS CP-3 Digital Surround Processor Television sound playback presents a challenge simply because of the wide Television variety of recording and processing techniques used in program produc- tion and transmission. Programs and commercials are recorded in mono, stereo, and surround sound, then subjected to compressors, erratic stereo synthesizers, sleepy production interns, and other electronic tortures.

  • Page 17: Music Surround

    When music is played, any loud instrument or sound effect is reproduced from the front speakers, not distractingly located off to the side. Lexicon PLUS is designed to optimally play...

  • Page 18: Full Range

    PLUS CP-3 Theory and Design PLUS CP-3 Digital Surround Processor Rear speakers in Music Surround (as in the other Surround modes) are driven by the THX enhanced surround signal. The front left and right outputs are attenuated by the volume and balance controls, but are other- wise unaltered by the processor.
  • Page 19 — whether you select classic monaural movies or the latest releases with all of their special effects — simply by changing modes. Lexicon incorporates it into the THX mode.

  • Page 20: Mono Logic

    CP-3 PLUS Digital Surround Processor Mono Logic is a surround conversion mode for monaural film sound tracks. A quick look through any video rental selection will prove the usefulness of such a mode; a large percentage of titles are mono. The problem of mono-to-stereo conversion is an old one.

  • Page 21: Pro Logic

    However, the left and right signals still contain dialog too, so the dialog is spread out among the three front speakers. Similarly, the Dolby Surround decoder takes all out-of-phase signals and sends them to the surround speakers, while leaving the original out-of-phase components in the left and right front speakers. Lexicon...
  • Page 22 PLUS CP-3 Digital Surround Processor The basic Dolby Surround decoder has high channel separation between left and right decoded audio, and between center and surround. The separation between left or right and center, or between left or right and surround, however, is only a few dB. The simple Dolby Surround decoder does pretty well with music (although sometimes the center channel is too loud) but, because any sound will be reproduced in at least three loudspeak- ers, effects are smeared and often unconvincing .
  • Page 23 Once one has heard some good examples of stereo surround channels the mono surround channel of Dolby Surround is no longer satisfying. As most of the information in the surrounds is ambient information and Lexicon PLUS PLUS PLUS...
  • Page 24 Pro Logic decoder, so full compatibility is maintained. The action of the decoder has been extensively tested both at Lexicon and at Lucasfilm to ensure the intent of the film director is accurately reproduced.
  • Page 25 The Subwoofer Crossover feature enables the subwoofer speaker to repro- duce only frequencies in the low bass range, leaving the front, center, sides, and rears to reproduce frequencies above 80 Hz. This facilitates optimum placement for imaging and smoothness, protects smaller speakers, and uses amplifiers more efficiently. Lexicon...
  • Page 26 PLUS CP-3 Theory and Design PLUS CP-3 Digital Surround Processor Re-Equalization is provided as a control to compensate for the fact that the soundtracks in films sound "bright" when listened to in a home environ- ment. This results from a combination of the way we perceive sound in large halls vs.

  • Page 27: Speaker Placement

    The Center speaker should be located directly beneath or above the screen (shielded.) — Turning on its side a speaker which is designed to be used vertically will significantly alter the sound wave patterns it is intended to produce. Lexicon...
  • Page 28 PLUS CP-3 Theory and Design PLUS CP-3 Digital Surround Processor Right, Left and Center speakers should be positioned at equal heights and at equal distances from the front wall. Depending on their height, they should be tilted to aim vertically at the listening area — they should not necessarily be angled in from the side walls toward this area.

  • Page 29: The Listening Room

    This can often be done by adjusting speaker placement, by altering room furnishings or by some combination of both, but to do this effectively, we must look briefly at the kinds of interference you may encounter. Following are some basic problems and suggested solutions. Lexicon...

  • Page 30: Room Reflections

    CP-3 PLUS Digital Surround Processor Room reflections cause blurring of the image of a localized front sound- stage. Sounds which are ideally perceived as coming from the screen, reach the listener from other directions, spoiling the illusion. These unwanted reflections can be eliminated by placing absorbent or diffusive material at the point of reflection.

  • Page 31: Structural Resonance

    Although surround speakers require some reflected sound to be effective, these reflections should be diffusive — providing randomized reflections in many directions. Bookcases and other irregular surfaces provide this sort of diffusion, as do some commercially-available acoustic panels. Lexicon...
  • Page 32 PLUS CP-3 Digital Surround Processor Creating a Custom Concert Hall Seat PLUS The CP-3 allows you to create virtually any acoustic space you desire. It is extremely simple to walk through the parameters of a program, vary them to your liking, name the space, and store it. For this example, let's do a fairly radical redesign —...
  • Page 33 13. Bradley, J.S., “Contemporary Approaches to Evaluating Auditorium Acoustics”, Proc. of the AES 8th International Conference, 1990, pp. 59-69. 14. Griesinger, D., “Beyond Dolby Surround — a seven-channel decoder for two-channel music and standard surround films”, Audio Eng. Soc. Con- vention N.Y., Oct., 1991. Lexicon...
  • Page 34 Lexicon Lexicon, Inc. 3 Oak Park Bedford, MA 01730 USA Tel 781-280-0390 Fax 781-280-0490 Lexicon Part #070-08806 Rev 2 Printed in the United States of America...

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