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Lexicon CP-1 Theory Of Operation
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Lexicon CP-1 Theory Of Operation

Lexicon CP-1 Theory Of Operation

Multi-channel music & cinema systems theory and design
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Multi-Channel
Music & Cinema
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Summary of Contents for Lexicon CP-1

  • Page 1 Multi-Channel Music & Cinema Systems Theory Design...
  • Page 2 Lexicon, Inc. Copyright ©1999 Lexicon. Inc. All Rights Reserved. Lexicon Patent: U.S. no. 4, 862, 502; other patents pending on the DC-1, DC-2 and MC-1. Lexicon, Inc.• 3 Oak Park • Bedford MA • 01730-1441 USA • Tel: 781-280-0300 • Fax: 781- 280-0490 CompuServe: GO LEXICON or 71154,1331@compuserve.com •...
  • Page 3 Multi-Channel Music & Cinema Systems Theory Design...
  • Page 4 Theory and Design Introduction All of the Lexicon home theater surround sound processors have a common goal: to draw you, the listener, more deeply into a musical performance or a film. For music, we use true stereo digital processing to recreate the original recording space or to create a new one of your choosing.
  • Page 5 The requirements for processing sound for home theater are somewhat different than those for music and our surround programs meet all of these requirements. Lexicon invented the technology that permits the most accurate reproduction of film sound in the same system that is used for music listening, and our software-based processors are optimized for each of these unique tasks.
  • Page 6 Low Frequency Effects channel (LFE). Lexicon processors use six of their eight discrete 24-bit D/A converters to decode these 5.1 channel encoded signals. In addition to standard decoding for both Dolby Digital and DTS soundtracks, we also include our proprietary Logic 7 matrix technology to extend the 5.1 stan-...
  • Page 7 Schroeder made binaural recordings in many halls. These recordings, played back through earphones, gave excellent reproduction of spatial qualities. Unfortunately, the stereo image tended to appear entirely inside the head, spoiling the accuracy of such recordings for some listeners. Lexicon...

  • Page 8: Theory And Design

    This technique, generically known as interaural crosstalk cancellation, was found to work well even without the anechoic chamber, and music pre- sented this way can be quite enjoyable. Lexicon incorporated this technique in many products as “Panorama”. Dwane Cooper coined the name “transaural reproduction”...
  • Page 9 Achieving all of these conditions is the guiding principle behind the Lexicon processors. Lexicon...
  • Page 10 When this is done the room becomes quieter and clearer, but not in any way like the original hall. Lexicon processors resolve this deficiency by supplying appropriate signals to loudspeakers at the sides of the listener. Our processors give the listener...
  • Page 11 Thus, the optimal system uses a Small center speaker setting — whether the speaker is capable of full range operation or not. Ideally, the center speaker should be set to 120Hz crossover. Lexicon...
  • Page 12 Multi-Channel Music & Cinema Systems Theory and Design Ambience Extraction The Panorama and Surround effects extract the original acoustic cues from the recording and present them to the listener from the correct directions. We call this ambience extraction. The Panorama effect can do this even with only two loudspeakers.
  • Page 13 Loudspeakers placed on either side of the listening position are the most effective and foolproof way to produce added Spatial Impression. Since it is not always possible to have side loudspeakers, Lexicon processors use crosstalk elimination to simulate them when they can’t physically be there.
  • Page 14 This works extremely well when the room is well damped and the listener’s head is correctly positioned. The first order devices described earlier required the listener to sit on the center line between the loudspeakers, and to arrange the angle between the speakers to correspond to the modeled delay.
  • Page 15 Left minus Right signal which can be sent to the side and rear loudspeakers. The delay is adjustable, as is the treble rolloff. For a listener in the ideal position, Panorama, with surround (side or rear) speakers, gives a nearly ideal re-creation of the original recording area. Lexicon...
  • Page 16 Panorama is also used as an element in the ambience and reverb simulation effects, where it can synthesize side loudspeakers which are not present in the installation. In these effects, the stereo inputs to the processor are fed directly to the front loudspeakers, with the digital outputs mixed in accord- ing to the setting of the processor's Effect Level control.
  • Page 17 The ambience simulation is done in stereo. Instead of feeding a monaural signal derived from the combined left and right channel inputs, Lexicon processors have two input points corresponding to instruments placed on the left or right side of the stage. From these, the loudness and delay of the reflections for the side and rear loudspeakers are calculated.
  • Page 18 The effectiveness of the ambience simulation is heavily dependent on the source material and the playback room. If the playback room is large and reverberant, its reflections may dominate those generated by the processor. Carpet, drapes and furniture can all be used to break up or absorb undesir- able reflections, making it easier to hear the processor’s output.
  • Page 19 Delay and reverb in the rear can occasionally be helpful but the ear is not particularly good at distinguishing between front and rear sounds and, as with the ambience effects, it is at the sides that reverb information is most needed. Lexicon...
  • Page 20 Lexicon processors are able to optimize the listening experience of any material precisely because they provide such a wide range of processing options.
  • Page 21 In the preset version of TV Matrix these parameters are set for pleasing results with a wide variety of program- ming, but they can be changed to produce a versatile mode for film sound — and some music as well. Lexicon...
  • Page 22 With Lexicon processing, additional speakers located near the sides of the listeners can add to the playback spaciousness. In the ambience and reverb...
  • Page 23 A High Pass parameter allows you to remove bass from side and rear speakers which might not be able to handle it. Center Level and Subwoofer Level controls are also provided. This effect is primarily useful for large audiences, or background music when entertaining. Lexicon...
  • Page 24 Multi-Channel Music & Cinema Systems Theory and Design Film Surround The goal of the film surround effects is to maximize viewer involvement and to faithfully reproduce the director’s intentions for the soundtrack in your own listening environment. Before explaining the way each of the film surround effects (Mono Logic, Pro Logic, THX Cinema, TV Matrix, and Logic 7) accomplish this goal, it is important to understand something about the way film soundtracks are made and presented in the theater.
  • Page 25 Multi-Channel Music & Cinema Systems Theory and Design Research at Lexicon has taken the possiblities of THX decoding to a further level with the introduction of true 7 channel decoding using a stereo surround process. This option is available via the Surround Effect param- eter in THX Cinema, and is further refined in the Logic 7 effect.
  • Page 26 The problem of mono-to-stereo conversion is an old one. One time-honored solution is to break the incoming signal into frequency bands, sending some to one channel and the rest to the other. When the filters are complementary (when the sum of the two output channels equals the original input channel) this solution can give stereo spread without ruining the tonal balance.
  • Page 27 This is a form of directional steering. Properly done, steering prevents the dialog from appearing in the other channels and enhances its plausibility. Lexicon...
  • Page 28 Some non-Pro Logic decoders reduce these side-channel sibilants by narrowing the spread of the front channels in the presence of dialog; this compromise is unnecessary in Lexicon processors. Multi-Channel Music & Cinema Systems Theory and Design...
  • Page 29 Lexicon decoders are unusual in a number of ways. First of all, our processors are entirely digital. (Most surround decoders advertise that they are digital because there is a digital delay line for the surround channel but the matrix and the logic decoding are done in analog.) Because our proces-...
  • Page 30 This is important because it is the side speakers which are most capable of delivering fully spacious and strong bass to the listening area. 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 31 The LFE channel delivers deep bass information for special effects and music soundtracks, but is not always used. Recordings made without the LFE channel are referred to as "5.0" soundtracks. Lexicon...
  • Page 32 Lucasfilm now offers two levels of THX certification. THX Ultra is the highest level of THX certification, and all Lexicon controllers meet these stringent requirements. All references here are to the THX Ultra standard. As a complete discussion of the theory of THX design is beyond the scope of this booklet, we refer you to LucasArts for detailed information on all aspects of the Home THX Cinema system.
  • Page 33 Some people, however, find that these natural changes in timbre are undesirable in a film. Timbre-Matching provides equalization to the surround channels, reducing the perceived change in character of sounds which are panned from the screen into the surrounds. Lexicon...
  • Page 34 Lexicon 5.1 Enhancements crossover, and adaptive de-correlation enhancements of 5.1 THX with Lexicon’s Logic 7 matrix technology. 5.1 Logic 7 and DTS Logic 7 differen- tiate between the side and rear speakers with a combination of delay and directional steering. For soundtracks with music or effects such as wind noise or applause, this creates a more spacious and enveloping soundfield and has a large effective listening area.

  • Page 35: Speaker Placement

    The Center speaker should be located directly beneath or above the screen (shielded.) Turning a speaker which is designed to be used vertically on its side will significantly alter the soundwave patterns it is intended to pro- duce. Lexicon...
  • Page 36 Multi-Channel Music & Cinema Systems Theory and Design 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 37: 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 38: Room Reflections

    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 39 Structural resonance (pictures and windows rattling. etc.) can be caused even by desireable bass frequencies. If the bass response of your system is at the desired levels, these rattles can be eliminated by putting felt on picture frames, or around window cracks. Lexicon...
  • Page 40 The listener should not be able to pinpoint the source of surround effects, therefore output from the surround speakers should not be aimed directly at the listening area. This is easily accomplished by raising the surround speakers. Although surround speakers require some reflected sound to be effective, these reflections should be diffusive —...
  • Page 41 12. Griesinger, D., “Multichannel matrix surround decoders for two eared listeners”, Preprint from the Los Angeles Conference of the AES, Nov. 1996. 13. Griesinger, D., “Spaciousness and envelopment in musical acoustics”, Preprint from the Los Angeles Conference of the AES, Nov. 1996 Lexicon...
  • Page 42 Lexicon, Inc. 3 Oak Park, Bedford MA 01730-1441 USA Telephone: 781-280-0300 Fax: 781-280-0490 Lexicon Part #070-13233 Printed in the United States of America...

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