1 DOCUMENT RESUME EM 000 327 ED 022 369 By- Wiens, Jacob H. MULTIPLE GENERATIONS ON VIDEOTAPE RECORDERS. and School LibraryEducation. California State Dept. of Education,Sacramento. Bureau of Audio-Visual Spons Agency-Office of Education(DHEW), Washington, D.C. Repor t No- ESEA -5; NDEA -3 Pub Date 68 Note-43p. EDRS Price MF -S025 HC-S1.80 EVALUATION, EQUIPMENTMAINTENANCE, Descriptors-COSTS, EDUCATIONALEQUIPMENT, *EQUIPMENT DESIGN, *VIDEO TAPERECORDINGS EQUOvENT STAMARDS,*EXPERIMENTS, RESEARCH 6401, Sony EV200, Sony Identifiers-Ampex VR6000, AmpexVR7000, Ampex VR7500,Concord VTR600, Craig PV120U, Sony SV300, WollensalcVTR150 recorders were testedfor their dubbingcharacteristics Helical scan video tape two in order tomake selection dataavailable to mediapersonnel. The equipment, by the manufacturers.The test was recorders of each typetested, was submitted of a single tape, designed to producequality evaluationsfor three generations levels of probable use inthe school situation.The experiment thereby encompassing all playing the recording tested four conditions:making a recordingand playing it back; making a copy of therecording and playing itback; and back on a second machine; in the study making a recording ofthe copy and playing itback. This representation waveform monitor, whichhas meaning forthe appears in twoforms: on the standard For each engineer; and on apicture monitor,which has meaning tothe media specialist. conditions, still photographsof the waveformoscilloscope of the four experimental performance and for image and the picturemonitor image weremade to analyze the recorders studieddetermine reproduction in the report.Various design elements in of their value for various uses.The conclusion is thatthere are three groupings quality and price range.When the intended usehas been recorders based on picture from one of the determined, the appropriategrade of machine maythen be selected groups.(PIT) 0 0 U I 0? 0 ocsrir =op iFteE3or a 0 CALIFORNIA STATEDEPARTMENT OF EDUCATION SUPERINTENDENT OFPUBLIC INSTRUCTION MAX RAFFERTY 1968 SACRAMENTO U.S. DEPARTMENT Of HEALTH, EDUCATION & WELFARE OFFICE Of EDUCATION THIS DOCUMENT HAS BEEN REPRODUCED EXACTLY AS RECEIVED FROM THE PERSON OR ORGANIZATION ORIGINATING IT.POINTS Of VIEW OR OPINIONS STATED DO NOT NECESSARILY REPRESENT OFFICIAL OFFICE Of EDUCATION POSITION OR POLICY. MULTIPLE GENERATIONS ON VIDEOTAPE RECORDERS 0 Prepared by Jacob H. Wiens Director, College of the Air College of San Mateo For the Bureau of Audio-Visual and SchoolLibrary Education California State Department of Education This manuscript was prepared under Standard Agreement No. 3404 by Wiens Electronics Laboratories 130 Crest Road Woodside, California It was reproduced with NDEA, Title III, and ESEA, Title V funds. PREFACE the dubbing characteristics The purpose of thisstudy was to investigate personnel may have of helical scan video tapedevices so that media make more graphically presented dataavailable to allow them to The representa- realistic appraisals ofmachines underconsideration. which has meaning tion in this study is on astandard waveform monitor which has more meaning tothe to engineersand on a picture monitor reproduced electricalcharacteris- media specialist. In the former, the visual or pictorial tics are represented;and in the latter, a representation is presented. by the manufacturers The equipment examined wasvoluntarily submitted invited to supervise thetests and for testing.Their engineers were to assure thatthe equipment wasfunctioning properly. for by the StateDepartment of The tests on themachines were arranged National Defense Education Education and werefunded in part by the should be made for thework of the team Act. Special acknowledgments the tests under the of electronicsspecialists which conducted Audio-Visual and SchoolLibrary direction of Guy M.Helmke, Bureau ot of Dr. Jacob H. Wiens,Director of Education. The team was composed Chief Engineer, KCSM-TV; the College of theAir; Francis J. Morgan, from the College of and Walter C. Nichol,Technician, KCSM-TV; all this report do San Mateo, San Mateo,California. The conclusions of recommendations of anyState not necessarilyreflect the official agency Harry J. Skelly,Chief Donald E. Kitch Bureau of Audio-Visualand Acting Chief Education Division of Instruction School Library Preface Introduction 1 Helical Scan Tape Recorders 1 Video Quality Test 2 The Test Procedure 3 The Test Sony EV-200 6 Sony SV-300 9 Sony PV-120-U 11 Ampex VR-7500 13 Ampex VR-7000 17 Ampex VR-6000 20 Wollensak VTR-150 22 Concord VTR-600 25 Craig 6401 28 Equipment Reliability 31 Tape Guides 31 Cleanliness 32 Cleaning Solution 32 Tape Tension 33 Tape Interchangeability 33 Standard Tape Format 33 Tape Costs 34 Gre lings Among Tape Recorders 34 Video Tape Recorders Tested 36 Test Equipment Used 37 Multiple Generations on Video Tape Recorders Introduction Video tape recorders have now become an integral part of oureducation program. The video tape recorder makes it possible to record material for review and instruction, as well as.to provide the means for storing instructional material for subsequent playback. Ideally, the video tape recorder should be capable of playingback the recorded material without degradation. This means that the picture as viewed on a picture monitor on playback would be as good as the original picture. The state of the art has advanced to the point where it is physically possible with the highest quality equipment to produce a recorded picture that cannot be distinguished by the eye from the original picture. The cost of this equipment, however, is high and, the atten- tion of many school administrators is focused upon the less expensive and more portable helical scan type of video tape recorder. Moreover, in addition to making ehe initial video tape, educators see a need to make copies of tapes. Any deterioration of picture quality in the process of recording and playing back will have a negative effect on the final product. It is hoped that this test may serve as an aid in determining whichof the helical scan video tape recorders present capabilities which promise to fulfill the planned needs of educational programs. Helical Scan Tape Recorders The equipment investigated and studied in this report is limited to the helical scan type video tape recorder. In the helical scan machine, the signal is laid down on a slant across the video tapl. The industry is currently producing helical scan video tape recorders in the two- inch, one-inch, and half-inch format. The two-inch format machine tested in this series is the Sony PV-120-U. A large number of mechanical configurations are used to make contact between the video tape and the recording head. A simple configuration uses a 1800 tape-wrap and two recording heads so that one head is constantly in contact with the video tape. This configuration requires a head switching assembly thatcomplicates the mechanical adjustment. In another configuration, the tape wraps entirely around the drum of the head using a conical wrap. This is sometimes referred to as an alpha wrap because of its similarity to the Greek letteT a. The alpha- wrap machines generally employ asingle head. The most common tape configuration, the omega wrap, uses a wrap which makes a loop around the head very similar to the Greek letter "omega" fl. This type of machine usually uses a single head. encountered machines isthe difficulty fault in allhelical scan impossible A common track to thenext. It is virtually in switchingfrom one slant from ehe endof one with ehe headin passing to maintaintape contact is easily next line. This difficulty line to thebeginning of the in whichehe configuration inthe omega wrap observed fromthe tape in passingthrough of contactwith the tape head iscompletely out In the AmpexVR-7000 of the tapetraverse. the smallbottom segment lines aremissing approximately eightfull video series, forinstance, 57. with the tape, seeFigures 55 and due to lossof head contact with thevideo machine thehead loses contact Since in thehelical scan reproduced bythe of time, no syncpulses are tape for asmall segment time, themonitor or this timeinterval. During this of recorder for by virtueof the behavior to afree-running state receiver reverts When the syncpulses are again oscillator circuit. period of time the horizontal oscillator huntsfor a short transmitted, thehorizontal time is a the syncpulses. The recovery before againlocking with oscillator drivecircuit of thehorizontal function of thetime constant involved. and differswith thecircuitry of the local pulses and thesubsequent hunting The momentaryloss of sync the videopicture results in adisplacement of horizontal oscillator video picture, in the upperportion of the and sometimesin a "hook" depends uponthe dura- of thisdistortion see Figure53. The severity adjustment onthe video pulses, thetension tion of theabsence of sync tape, andehe electroniccircuitry. the videopicture is drop-out withrespect to The locationof the head to occur near drop-out in allmachines is made important. The head is justbefore pulses and themostfavorable location the vertical sync With the headdrop-out located of vertical syncpulses. oscillator has the the series the horizontal point in thetime sequence, information of the at this the firstpicture longest time tostabilize before next fieldis reproduced. phenomenon is animportant head drop-out The problempresented by the head-to-tape material. The loss of one inmaking copiesof the video time material shouldfall at the same contact onehe re-recorded