Dolby Laboratories CP65 manual Adjustment of Surround Delay, Thumbwheel Switch, Msec Setting

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5-42

B-Chain Alignment Procedures

f. Adjustment of Surround Delay

The CP65 incorporates a delay line in the surround channel to ensure that sound from the rear of the theatre arrives at the listeners’ ears approximately 20 milliseconds after the arrival of sound from the front speakers.The delay is set into the Cat. No. 150 card via a thumbwheel switch by using the following formula:

1.The distance between a rear seat and the nearest surround loudspeaker, in feet, is estimated. If the metric system is used, convert the distance from meters to feet by multiplying by three (3).

2.The distance from this seat to the front loudspeakers is estimated, in feet. If the metric system is used, multiply the distance by three (3) to convert distance from meters to feet.

3.Subtract the distance in 1 above from the distance in 2 above.

4.Add 20 to the difference in 3. above to obtain the delay time, in milliseconds.

Determine the Cat. No. 150 card thumbwheel switch setting (delay line setting) from the table below.

Delay Time

Thumbwheel Switch

(msec)

Setting

30

1

40

2

50

3

60

4

70

5

80

6

90

7

100

8

110

9

120

10

130

11

140

12

150

13

For example:

The selected seat is 10 feet (3.3 meters) from the surround speakers.

The selected seat is 80 feet (26.7 meters) from the front speakers.

The delay is set for (80-10) + 20 = 90 milliseconds — switch position 7.

5-43

B-Chain Alignment Procedures

f. Adjustment of Surround Delay

You can verify that the delay setting is acceptable by listening to a familiar Dolby Stereo film which ideally contains both center channel dialogue and some discernable surround sound. The Dolby Cat. No. 251 “Jiffy” film serves excellently for this purpose. If a stereo film is not available, the delay time can be checked with a mono film if the film is played in format 04 Dolby stereo optical with surround. Before you set the delay time, set the individual level adjustments for each channel because the subjective effects of channel level and delay time interact somewhat. Make certain all speakers are ON for this test.

While the film is playing, walk around the theatre and carefully listen to the surround speakers when there is center channel dialogue. The dialogue should appear to be coming from the screen with no significant dialogue coming from the surround speakers.

If you hear discernable dialogue from the surround speakers, the delay time was probably set too long.

If you hear an objectionable amount of dialogue from the surround speakers, which persists regardless of the delay time setting, there is probably severe gain or azimuth error in the system. Recheck both the Dolby level and the A-chain alignment of the optical system.

In many films, the surround information is intended for subtle effects and may provide only a low-level ambience. If the surround level and delay time have been adjusted as previously described, the surround information will be at the level desired by the film director. Do not be tempted to increase the surround level because the effect desired by the film production team may be impaired or destroyed.

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Contents Model CP65 Cinema Processor Dolby Laboratories Inc Headquarters Table of Contents Section Reference Block Diagrams Introduction Page Section Equipment Required Smpte Buzz Track Stereo Optical Surround Level Cat. No Jiffy Test Film Cat. No 2 Listen . . . Film Cat. NoSection Initial SET-UP and Installation Voltage Acceptable Setting Voltage Range Fuse Type Next, check the jumpers in the following locations Cat. No , Power Supply Module Cat. No , B-Chain CardCat. No , Control Logic Card J2 NON-SYNCCP65 Backplane Standard CP65 or CP65ACP65-300 High Low Subwoofer subwoofer Output output These Modules are Necessary for Bypass Operation Slot Card Function Cat. No Two-channel NoiseReduction Module Channel DecoderContains a semi-regulated power supply with Voltage Setting Fuse Type InternationalIEC Notices HUM Problems Room lighting dimmer controls SCR-TYPEPage Section AN Overview of the Alignment Procedure Aligning the B-ChainPage Page Section Chain Alignment Preliminary Procedures Action IndicationLamp Voltage Optical Preamplifier Adjustments Chain Alignment Procedures Optical Preamplifier Adjustments 222 CAT. no Test Film Oscilloscope Traces Repeat CAT no Repeat 1 →Magnetic Preamplifier Adjustments Magnetic Alignment 100mV Section Chain Alignment Setting Room Equalization BypassLoudspeakers and Crossovers Amplifiers GeneralChain Alignment Procedures OffRepeat ActionChain Alignment Procedures Setting Room Equalization Do not adjust Paul Setting Room Equalization b. Adjusting L,C,R Gain 14 → 21 R 14 →Setting Mono Gain 79 dBCChain Alignment Procedures Subwoofer Alignment Cat. No 90 dBC 85 dBCFrom Step NoSelect format 04 Dolby Stereo A-Type Same AS 441Surround Equalization Alignment Cat. No Surround Equalization Alignment Cat. No Notes Cat. No 441Desired 88 dBC Bypass Adjustment of Surround Delay Thumbwheel SwitchMsec Setting Chain Alignment Procedures Adjustment of Bypass Gain Xx dBCFrom Xx dBC -3 dB Yy dBCAdjustment of Non-sync Gain Press the format 60 non sync switchAuto Freq Adjustment of Mono Gain and Equalization Notes Repeat page 5-20 StepChain Alignment Procedures Final Checks Press the format 04 Dolby Stereo A-type switchSection Reference Diagrams Cat. No Dual Noise Reduction Module Inputs Cat. No Optical Bass Extension and Surround Equalizer Card Cat. No B-Chain Facilities Card Cat. No Power Supply Card Cat. No Transformer Module Inputs Cat. No Control Logic Card Cat. No +24V +15V 15V +12B+15M Appendix a Checking Phasing of Speakers Appendix B Effect of Changes in Slit Height on Slit Losses Appendix C CP65M Mono Instructions OperationCat. No a Circuit Description Schematic Cat. No a Appendix D Backplane Connections List Terminal Block TB3Connector J18
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