Dolby Laboratories CP45 User Manual

MODEL CP45 CINEMA PROCESSOR

Users' Manual

USERS' MANUAL

FOR

MODEL CP45 CINEMA PROCESSOR

Dolby Laboratories Inc

U.S.A. 100 Potrero Avenue, San Francisco, CA 94103

Tel: 415-558-0200; Fax: 415-863-1373

U.K. Wootton Bassett, Wiltshire SN4 8QJ, England

Tel: 01793-842100; Fax: 01793-842101

Dolby is a registered trademark of Dolby Laboratories Licensing Corporation.

ISSUE 1

S95/10750

Dolby Part No. 91388

TABLE OF CONTENTS

INTRODUCTION

SECTION 1

OPERATING INSTRUCTIONS ............................................................................................ 1-1

A. NORMAL OPERATION

1. Initial Power-Up..................................................................................................1-1

2. Format Selection..................................................................................................1-1

3. Local (Front-Panel) Fader..................................................................................1-3

4. Remote Faders .....................................................................................................1-3

5. Mute Function......................................................................................................1-3

B. OPERATION WITH AUTOMATION SYSTEM ....................................................... 1-4

C. BYPASS OPERATION................................................................................................... 1-4

SECTION 2

MAINTENANCE AND ADJUSTMENTS........................................................................... 2-1

A. SOUNDHEAD MAINTENANCE............................................................................... 2-1

B. PRINT CLEANLINESS .................................................................................................. 2-2

C. DOLBY LEVEL ADJUSTMENT................................................................................... 2-2

SECTION 3

TROUBLESHOOTING ............................................................................................................ 3-1

A. DURING THE SHOW

1. If Film Sound Is Lost ..........................................................................................3-1

2. If One Channel Fails or is Distorted ................................................................3-2

3. If Switching to Bypass Does Not Restore Sound ..........................................3-2

4. Excessive or Inappropriate Sound from the Surround Speakers .............3-3

B. BETWEEN SHOWS ........................................................................................................ 3-3

C. WHEN THE THEATRE IS CLOSED .......................................................................... 3-4

D. TROUBLESHOOTING CHART .................................................................................. 3-6

APPENDIX A HOW TO TELL A STEREO OPTICAL PRINT

FROM A MONO PRINT ........................................................................................................A-1

APPENDIX B

DOLBY TEST AND DEMONSTRATION FILMS........................................................... B-1

1. Cat. No.69T: Dolby Tone ................................................................................ B-1

2. Cat. No.251: Jiffy Test Film ............................................................................ B-1

3. Cat. No.351 Stereo Demonstration Film: “listen . . .” ............................... B-3

4. Other Test Films ................................................................................................. B-3

APPENDIX C

CP45 MODULE DESCRIPTIONS........................................................................................ C-1

APPENDIX D

ABOUT DOLBY FILM SOUND FORMATS .....................................................................D-1

1. How Dolby Noise Reduction Works ..............................................................D-1

2. About Dolby SR..................................................................................................D-1

3. Why the Dolby Level Adjustment Is Important..........................................D-3

4. The Consumer Dolby Noise Reduction Systems .........................................D-3

APPENDIX E HOW FOUR CHANNELS ARE DERIVED FROM

DOLBY STEREO OPTICAL PRINTS...................................................................................E-1

APPENDIX F

OPTICAL BASS EXTENSION ...............................................................................................F-1

APPENDIX G CINEMA SOUND AND THE EVOLUTION

OF DOLBY FILM SOUND.....................................................................................................G-1

INTRODUCTION

WHY A CINEMA PROCESSOR?

Originally, stereo sound on motion picture film was possible only by means of magnetic striping, which was introduced in the 1950s. Although capable of very good sound, this was such a costly approach that by the 1970s relatively few films were being released with stereo soundtracks.

Then in 1975 Dolby Laboratories introduced the stereo optical soundtrack originally known as Dolby Stereo. It provided the multichannel sound associated with magnetic soundtracks in a much more practical format.

Getting high-quality stereo sound from an optical soundtrack required the application of several new processes. It was necessary, for example, to electronically “fold” four sound channels into just two physical tracks on the film, and then “unfold” (decode) them on playback in the theatre. Dolby noise reduction, a form of signal processing that greatly expands the limited dynamic range of optical soundtracks, was also used, and requires its own special playback processing circuitry.

Thus the cinema processor was introduced as a new element in theatre sound systems. In addition to properly decoding Dolby encoded soundtracks, Dolby processors such as the CP45 also provide equalization circuits that optimize the frequency range of the projector’s optical soundhead and the theatre loudspeakers. The diagrams below show the role cinema processor plays in bringing your audiences thrilling, multichannel Dolby sound.

About The Dolby CP45

Once installed, the Dolby CP45 Cinema Processor becomes the heart of your theatre sound system. All sound sources are connected to the CP45, which processes their signals appropriately and feeds them to the power amplifiers.

The Dolby Model CP45 provides the high performance for which all processors manufactured by Dolby Laboratories are known in a new cost-effective, integrated design. Its many features include a stereo optical preamp with precise slit-loss correction, processing for both Dolby A-type and Dolby SR soundtracks, an advanced 2:4-channel decoder, and multi-band screen speaker equalization. These advanced circuits ensure accurate reproduction of all films with Dolby analog soundtracks, and permit the theatre to use the widelyrespected name “Dolby” on the marquee and in advertising to identify presentations of Dolby releases.

Additional standard features of the CP45 are a built-in fader with remote facilities, simple push-button soundtrack format selection, and comprehensive fail-safe features that include a built-in bypass system. The unit also interfaces readily with theatre automation systems.

The CP45 supports the following sound formats:

Format Number

Mono 01 Dolby A-type (stereo) 04 Dolby SR (stereo) 05 Non sync 1 60 Non sync 2 / Aux 61 Microphone 64

About This Manual

This Users’ Manual has been prepared specifically to help projectionists get the most from the Model CP45 and the theatre sound system once it has been installed and aligned. (Installation and alignment instructions are supplied to the local distributor or installation company). We suggest that you keep this manual readily available.

The manual is organized as follows:

• Section 1, Operating Instructions, covers the basic control functions and operation of the CP45.

• Section 2, Maintenance and Adjustments, contains tips for maintaining the CP45 and the theatre sound system.

iii

• Section 3, Troubleshooting, will help you track down problems in the sound system without test equipment. It consists of a troubleshooting chart and procedures to follow during a show, between shows, and after closing.

• The Appendices contain valuable background information which will help you to get the most out of the Model CP45 and your theatre sound system.

For the sake of clarity, boldface type is used for all specific references to the CP45 controls and their labels, such as Bypass, and front-panel Fader. In addition, indicator lights on the CP45 are referred to in the text as LEDs (lightemitting diodes).

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SECTION 1

OPERATING INSTRUCTIONS

A. NORMAL OPERATION

1. Initial Power-Up

Each time the CP45 is connected to power, it automatically sets itself to the format it was in when power was removed unless the power has been removed for more than a week. Under these circumstances the wake-up state is:

• Format 01 Mono

• Front-panel (Local) fader activated

• Proj 1 or Proj 2 LED illuminated, indicating the externally- selected projector that is active (Proj 1 can be set to be selected automatically if no external selection has been made although it is usual for the individual projectors to be selected for bypass mode flexibility).

2. Format Selection

Select the desired film soundtrack format or your non-sync source by pressing the appropriate button. The LED in the button illuminates to confirm that the format was selected. The formats are as follows:

• 01 Mono: for all optical prints of any vintage with conventional mono optical (“Academy”) soundtracks.

• 04 Dolby A-type: for Dolby Stereo releases, except those marked SR or Digital.

• 05 Dolby SR: for releases marked as having a Dolby SR soundtrack. (If your CP45 is not equipped with the SR circuit needed to play SR copies, 04 Dolby A-type can be selected.)

• 60 Non-sync 1: for your music tape or CD player.

• 61 Aux/Non-sync 2: this format may be programmed in a number of different ways depending on the optional equipment fitted and the installation. Possible options include:

Magnetic soundtracks from projectors or followers with appropriate magnetic preamplifiers.

Extra sound sources (consult your service engineer for details).

1-2

Figure 1. CP45 Front Panel Control

SignalSignal

SystemSystem

FormatFormatFaderFader

faderfader activeactive

NormalNormal

BypassBypass

LeftLeft

RightRight

CenterCenter

Sub WooferSub Woofer

SurroundSurround

MicMic

MonoMono

1010

Projector 2Projector 2

Projector 1Projector 1

Non-sync 1Non-sync 1

Aux/Non-sync 2Aux/Non-sync 2

Dolby Stereo A-typeDolby Stereo A-type

Dolby Stereo SRDolby Stereo SR

6161

6060

6464

0505

0101

0404

FADER ACTIVE INDICATOR

Shows if the front panel fader has been selected.

FRONT PANEL FADER

Controls the auditorium level when selected. The control should be set at or near 7 for normal operation.

PROJ 1/PROJ 2 INDICATORS

Show which projector has been selected.

Normal fader setting.

FORMAT 01

For mono optical soundtracks.

FORMAT 04

For Dolby Stereo soundtracks except those marked SR or SR•D.

FORMAT 05

For Dolby Stereo SR soundtracks.

FORMAT 60

For non-sync, background music from a cassette deck or CD player.

FORMAT 61

For extra sound sources.

BYPASS INDICATOR

Flashes if the CP45 is in

bypass mode.

The CP45 will automatically switch to

bypass if the internal power supply fails.

SIGNAL PRESENCE INDICATORS

These will light if a signal is present on the indicated channel.

BYPASS/NORMAL SWITCH

For manually switching to

bypass if there is a problem. Switches to a separate power supply.

FADER ACTIVE BUTTON

Switches the fader control back to local (this fader) if remote faders are installed.

FORMAT 64

Selects the microphone for public announcements. If the CP45 is in bypass mode, push and hold

this

button to make an announcement.

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• 64 Mic: for public address announcements in the theatre.

The film soundtrack format numbers used on the CP45 front panel often appear on the film can and leader. If these numbers are not supplied and you are not sure if a print is mono or stereo optical, see Appendix A for a means to distinguish mono from stereo optical soundtracks.

If you are playing an early Dolby Stereo release and it is marked as format 03 “Dolby Stereo without surround,” select format 04 Dolby A- type.

3. Front Panel (Local) Fader

The fader on the front panel of the CP45 controls the volume level in the theatre in all operating modes. After the CP45 has been correctly installed, setting the fader to 7 will play a Dolby film at the level at which it was mixed.

Although a minor adjustment in playback level might be required under unusual circumstances, you should avoid significant deviations from the correct level (7) established by the installer. If the playback level is set too low, dialogue will be hard to understand; too high a level will give rise to complaints from the audience and under extreme circumstances can damage the theatre’s sound system.

4. Remote Faders

In addition to the front panel (local) fader the CP45 can also be controlled by an external remote fader.

If a remote fader has been installed, it is activated by pressing the select button on the remote. The local front panel fader LED will go off to indicate that the remote fader has been activated. To regain local control, press the “fader active” button located below the front panel fader. The button will have no effect if there are no remote faders.

5. Mute Function

When you press the mute button on the remote unit (if installed), the volume will automatically fade all the way down. When you press the button again, the volume will automatically rise to the level set by the fader which is in control of the level (local or remote fader).

The Mute button is useful if the film breaks or runs out with the projector active since it supresses the very loud signal that occurs when a leader or tail passes through the sound gate.

If the CP45 is not conveniently close to the projector and there is a remote fader at the projector, use the following procedure to start the show:

1-4

• Fade out the intermission music with the local front panel fader.

• Move to the remote location and see that the fader there is at 7.

• Select the film format.

• Start the projector.

• After the film leader has passed through the gate, select the remote fader and trim the level slowly if necessary.

Following the above procedure should prevent the audience from hearing annoying thumps and leader crackle at the beginning of the show.

B. OPERATION WITH AUTOMATION SYSTEMS

If the CP45 in your theatre is connected to automation equipment, the format buttons and their associated LEDs may be duplicated elsewhere. In most cases, the front panel controls of the CP45 can usually be used to override commands from the automation system; however, as automation equipment differs from installation to installation, check with the installer of your system if you have any questions about its operation and whether you can easily override automation commands.

C. BYPASS OPERATION

The CP45 has an independent power supply for emergency operation. If the main power supply or processor circuitry fails, the unit will automatically switch to bypass operation, allowing the show to continue with limited sound processing functions. Bypass operation is signalled by the flashing of the bypass LED on the front panel.

In the case of other problems, such as distortion or the loss of a channel, the bypass mode can be selected manually by means of a switch located on the front panel. However, there are other components in the theatre sound system that could also fail. Be sure to refer to Section3, Troubleshooting, any time there is a problem.

The following occurs when the CP45 is switched into the bypass mode:

• The front-panel remains operational but remote faders will not work.

• Although you can select formats to help with faultfinding, the commands from the front panel are ignored by the unit. The optical preamp output of the selected projector and (if so programmed at installation) the Non-sync and/or Aux inputs all remain operational simultaneously. If you are not playing film,

1-5

be sure that the projector is not selected. If you are playing an optical film print, be sure that there are no signals present from any of the other sound sources.

• Even when a stereo print is playing, a summed mono signal is fed

to all the screen speakers. Thus, you can switch to the bypass mode to keep the show going if one of the power amplifiers or speakers fail.

• The Dolby A-type noise reduction circuitry, Spectral Recording processors, 2:4-channel decoder, screen speaker equalizers, surround equalizers, and subwoofer circuits are out of the signal path.

• The front panel mic switch acts as a "push to talk" key rather than a "push on, push off" switch. If there are emergency announcements to make, the film and background music should be turned off so that the audience can hear the announcement above the other sources of sound.

If the unit has entered bypass mode due to a failure in the main power supply or the main power source, then the front panel LEDs will be off except the projector select and bypass LEDs. The unit performs in exactly the same way as if the bypass switch were selected as described above.

In the event of bypass operation, be sure to follow the troubleshooting procedures and call your trained service engineer, if necessary, as soon as possible.

NOTE

The CP45 will not operate even in the bypass mode if there is a fault in the mains supply to the bypass transformer and may not operate if there is a fault in either the Cat. No. 514 optical preamp card, the bypass circuitry section of the Cat. No. 510 on which it is mounted, or the bypass power transformer itself. It is strongly recommended that a spare of both of the cards and the transformer block be kept on hand for substitution in emergencies. If the theatre is equipped with film platters and the unused projector input on the rear of the CP45 is accessible, the projector solar cell leads can be moved from P1 to P2 in order to try using the second optical preamp circuit, however this input may not be set up correctly so care will be needed with the volume control.

1-6

WARNING

The CP45 was adjusted initially by a specially-trained engineer so that your theatre would have the same standard playback characteristics as the dubbing theatres in which all Dolby encoded films are mixed. This results in the most accurate reproduction possible. Never attempt to

adjust any controls within the CP45 except those specified in this manual.

All other controls are for use by a trained engineer when the CP45 is first installed or repaired. Adjusting these controls requires the use of special test equipment. Misadjusting these controls can have an adverse effect on the sound in your theatre and will require a service call to restore proper operation. The first thing to do when you have a problem is to consult Section 3 Troubleshooting, and not randomly adjust these specialized controls.

In addition, do not adjust any of the controls on the other audio equipment in your theatre sound system such as power amplifiers, which have been preset by the installer. For example, misadjusting the power amplifier gain controls can cause channel imbalance and/or too much power amplifier noise. Those controls have been set by the installer for correct channel balance and so that the playback level in the theatre is correct with the fader set to 7. If a satisfactory level can only be achieved with the fader set to some other level, the gain controls on the power amplifiers have been touched and have now to be recalibrated by a service engineer.

2-1

SECTION 2

MAINTENANCE AND ADJUSTMENTS

The installation of the Dolby CP45 in your theatre indicates a commitment to providing a high-quality presentation to your audiences. However, the presence of even the very best equipment does not in itself guarantee the best results. A number of routine maintenance and adjustment procedures, requiring no special test equipment or technical knowledge, are necessary to realize the full potential of the sound system on a dayto-day basis. These procedures can also prevent costly show cancellations and service calls.

A Dolby Cat. No. 69T test film is required for proper maintenance of your sound system. We also recommend that you keep on hand the Dolby Cat. No.251 Jiffy Test Film and run it regularly to check the theatre sound system thoroughly (see Appendix B).

A. SOUNDHEAD MAINTENANCE

No single maintenance procedure is more vital to good sound in the theatre than regular cleaning of the projector soundhead optics. Use lint-free cotton swabs and isopropyl alcohol to clean the optical barrel lens surfaces, but, under no circumstances touch or attempt to clean the solar cell. The solar cell and its adjustment are extremely delicate. We strongly recommend that you use compressed air, available in convenient pressure cans, to blow dirt and debris away from the cell. But be absolutely certain that the nozzle cannot ever touch the cell.

Figure 1 Cleaning the Soundhead Optics

2-2

Figure 2 Never touch the solar cell

B. PRINT CLEANLINESS

A high fidelity Dolby Stereo theatre system is like a high-quality home stereo system: it can sound only as good as the program material played through it. A good theatre system will reproduce pops, crackles, and other unwanted noises from worn and dirty film prints.

If you receive a poor print from your distributor, there is little you can do except, if possible, arrange for its replacement. But while a print is in your theatre, you should treat it with respect and care to be sure your audiences receive the best in both sound and picture. Of greatest importance, the print should be kept as clean as possible—when the film is played, when the print is stored between shows, and when a platter reel is made up (if your theatre is so equipped). In particular, when individual reels are unwound to make up a platter reel, do not let the film touch the floor or come in contact with other sources of dust and dirt.

C. DOLBY LEVEL ADJUSTMENT

Proper decoding of soundtracks encoded with Dolby A-type or SR processors requires careful level matching between each channel of each soundhead and the CP45 (see Appendix D for a discussion of Dolby noise reduction and why Dolby Level is important). When the CP45 is first installed, the installer makes this adjustment for you. However, it is always necessary to adjust Dolby Level whenever an exciter lamp is replaced. We also recommend that you routinely check Dolby Level but only adjust it to compensate for the normal aging of the exciter lamp if necessary. Always clean the optics first.

Checking and adjusting Dolby Level requires a loop of Dolby Cat. No. 69T test film that is available from your theatre equipment supplier. You will also need the alignment tool supplied with the CP45 or a small screwdriver.

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