Videotape Program Production at

CBS Studio Center By WILLIAM G. CONNOLLY

The one-inch helical videotape recorder has been utilized by CBS to configure a film- plitude modulation and phasc modulation style (one VTR per camera) videotape production system at CBS Studio Center in do correlate well, particularly with PM Hollywood. Operating experience with these machines is discussed, with emphasis on noise, which is a measurc of color distor- observations of video, audio, and transport performance. I n addition, this paper tions. Subjectivcly, the results are better describes a unique system for synchronization of one-inch VTRs in post production that than that indicated by a simplc review of has allowed CBS to offer an alternative to traditional multi-camera videotape production signal-to-noise curves. Coherent picture methods. disturbances such as banding and first line error are usually more detrimcntal in Introduction that othcr recorders built to the SMPTE dubbing operations than signal-to-noise Type C standard will be capablc of equiv- loss. A nonsegmcntcd format is, of course, In February of 1975, CBS issued target frcc of those errors. specifications for the design of a videotape alent performance. The pcrformancc data were originally recorder with improved editing capabilities. Audio Performance Thc thrust of these specifications was for measured in mid-I976 on three pre-pro- duction prototypes. Machincs of later As can be secn in Tablc 11, frequency a recordcr with vastly improved transport response and signal-to-noise ratio approach characteristics, coupled with a tape format production runs have been compared and thc data proved to be typical of the 23 units that of studio-quality audio recorders. which would permit the display of viewable Harmonic distortion of 0.7% and wow and pictures at a varicty of speeds in both for- in service or currently being installed at CBS. flutter mcasured at 0.03% promise excel- ward and reverse. The intended application lent results. These results arc in large was for off-line cditing systems from which Video Performance measure due to a unique push-pull dual- a work copy would bc produced. The capstan design. camera originals would later bc conformed Typical video performancc is shown in Tablc I. All thc pcrformance data shown Thcrc arc three audio tracks in this for- through automatic assembly in an on-line mat, with Audio I and Audio 2 separated editing systcm. compare favorably with quadruplcx rc- corders, particularly in differential gain, by 0.8 mil (0.2 mm). These tracks can bc I t had bccome clear at that time that uscd to rccord sterco or independent audio computcr-assisted videotape cditing facil- phasc and moirt, but notc especially the improved interchange performancc. A signals. I n the latter case, crosstalk of -38 ities, such as thosc pioneered by CMX, had dB at 50 Hz and -50 dB at 100 Hz may become limited, not by software, but typical signal-to-noise ratio of 49.5 dB, coupled with an interchange loss in S N R seem unacceptable to the audio purist. through the inability of videotape recorders Howcvcr, the ASA “A” weighting curve to respond efficiently to commands without of only 0.2 dB, gives rise to excellent mul- tiple-generation performance. First-gen- comes to our aid at these frcqucncics. Lis- continual breakdown. Moreover, the cost tening tests confirmed the acceptability of of intcrfacing various VTR types and cration quadruplex performance is typi- cally 47 dB and interchange loss is 2.0 dB. the 0.8-mil separation; tcsting included models to computcrs had become an im- hard rock music passages which evidcntly pediment to economical dcsign. Clearly, This means that a tape recorded on one VTR and played back on another (the most have bccomc the acid test currently in favor VTRs with TTL-compatible command in the audio world. systcms were needed. usual kind of operation) would, typically, have an S N R of 45 dB for quad and 49.3 VTR manufacturers had also identified Transport Performance this problem. Less than six months later the dB for hclical. In other words, thc 1-in he- lical product is “up” more than one gen- Tape transport performance meets a first of scvcral laboratory prototypes was very high standard. Variable-speed search shown. The following year brought sevcral eration, compared with a quadruplex re- cording. is controlled by a dial with still framc at a more prototypes to light. More than centcrcd dctcnt. Clockwise rotation of the mccting many of thc criteria for an cditing Figurc 1 shows plots of noise perfor- mance versus number of generations for a dial moves the tape forward in increments systcm machine, howcvcr. they had an from still framc through 64 times play unforeseen advantage: the audio and video 1 -in hclical VTR. The uppermost curve shows wide-band speed, with the speed proportional to the signal performance challcnged that of ex- amount the dial is moved off ccntcr. isting 2-in quadruplex broadcast record- noisc measurements out to the twelfth generation. These tests wcrc made using Countcrclockwise motion performs the ers. same function in reverse. CBS chosc a nonsegmented or onc field three machines with a procedure which per scan video format from among those ensured that no recording was played back 1-in helicals offercd at that time. This on the machine on which it was made. format, later to be standardized as SMPTE (Time-base correctors were used for each Table I. BVH-1000 video performance. (Mea- Type C, has the inherent capability of of the 12 dubs.) Each generation, therefore, surements include BVT-1000 time-base correc- producing viewable pictures at many tape included an interchange loss and a dubbing tor.) speeds. Sincc that time a digital store has loss. Thc middle and lowcr curves show am- Frequency f0.3 d B from 30 Hz to 4.1 5 been designed to provide this capability responsc MHz; -3 d B at 4.5 MHz also with thc scgmented formats. plitude- and phase-modulation losses as measured on a Shibasoku (of Tokyo) 925C Signal-to-noise 49.5 dB unweighted CBS currently uscs the Sony BVH-1000 ratio in editing systcm designs and, necessarily, meter. The significance of these curves can Differential 3.0% thc data which follows describes that ma- only be adequately explained in a paper on gain chine. However, there is every indication that subjcct alone. Suffice it to say that Difl-erential 2.5O both the AM and PM noise curves are as phasc Prcsentcd on 3 February 1978 a t the 12th Annual smooth as the wide-band curve and that K-rating (2T 0.8% SMPTE Television Conference in Atlanta by William they also track that curve rather well. Our sin* pulsc) G . C onnolly. CBS Television Network. 51 W. 52 St., experiencc has shown that wide-band noise Moire (75% -43.0 d B New York, NY 10019. Copyright (0 1978 by theso- color bars) cicty of Motion Picturc and Television Engineers, Inc. measurements do not correlate well with the subjcctive evaluation of videotape sig- Interchange 0.2 dB Previously published in unedited form in the SMPTE loss (SNR) book One-Inch ffcliiwl Videotape Recording. nal degradation. On the other hand, am-

Volume 87 November 1978 SMPTE Journul 161

- 5 0 dB Table 11. BVH-1000 audio performance.

Frequency *0.6 dB from 50 Hz to 15 response kHz Signal-to-noisc 60 dB unweighted (ref.: ratio 3% THD at 400 Hz) 0 Harmonic 0.716 (ref.: 8 dB below I- distortion 3% THD at 1 kHz) 4 M Wow and 0.03% rms, NAB Y -40dB flutter unweighted Y Audio I / -38 dB at 50 Hz 0 Audio 2 -50dBat 100Hz z crosstalk -65 dB at 1 kHz 0 -57 dB at 15 c; kHz d< MODULATED NOISE Z 2 facilities, one a t CBS Television City in In Hollywood and the other at CBS Studio 51 PHASE MODULATED NOISE in New York. The Television City facility -30 dB is described in a separate paper by William C. Nicholls entitled “A New Edit Room Using One-Inch Helical VTRs” - see p. 764 in this issue of the Journal. 0 d B The Studio 5 1 installation is unique in 1 2 3 4 5 6 7 8 9 1 0 1 1 ’ one important sense. The system is dedi- GENERATION cated to a studio 30 blocks distant from Fig. I . BVH-1000m ultiple-generation performance. CBS Broadcast Center. Prior to the advent of lower-cost machines, the recorders would have been integrated into the Proportional control is actuated by the modc, vidco lock is achieved typically in 2 Broadcast Center complex for maximum samc dial through operation of a mode s. Three seconds is a safe preroll time. utilization, with local telephone-company button. Continuous clockwise rotation of Video lock-up time from the stop mode loops providing service to the off-premise the dial moves the tape forward in speeds requires about 13 s - most of which is studio. Now, however, the lower capital from still frame to one-fifth normal play consumed in bringing the scanner up to cost of the I-in VTRs has allowed four speed. The faster the dial is turned, the speed. Also, due in part to the use of ac machines to be dedicated to that studio faster the speed. Counterclockwise rota- servos throughout, the transition between alone. tion, of coursc, performs the samc function modes requiring high motor torque seems The third facility is different in many in rcvcrse. The best way to describe the sluggish. This is no doubt due, in large part, ways, principally because it is located a t a action of proportional control is that it is to conccrn on the part of the manufacturer film production facility - CBS Studio akin to grabbing the reels by hand and ro- to avoid tape damage. Center in North Hollywood. (The back- tating them, but with far greater con- Machine control is effected by means of ground leading to the design of this facility trol - and without the danger of tape a TTL-compatible interface internal to the is covered in a paper by Joseph A. Flaherty damage. recorder. A 64-bit word is used for each entitled “New Horizons in Television Initial reactions of editors using thew command and sent over a single bus in a Program Production, Post-Production and controls have been excellent. Finding the 200-kHz data stream. Machine status is Continuity” published in the September exact frame on which a camera cut was echoed over the same bus. An application 1977 SMPTE Journal.) made is quickly and easily done. of this system will be described later. The post-production editing system at Vidco display lock is, of course, a func- Studio Center is one portion of a special tion of both transport and time-base cor- Location of Facilities multi-camera videotape unit designed by rector for a given format. A color picture CBS has completed three videotape CBS to produce multi-camera film pro- is held quite satisfactorily in high-speed post-production editing installations since grams. In this application the electronic search at cight times play speed and a black June 1977. The three together use a total photography is done film-style, with a and white picture as fast as 40 times play of thirteen 1 -in helical recorders. videotape machine assigned to each cam- speed. Two installations, each with four ma- era. Since all the footage from each camera With the recorder placed in the standby chines, are in television studio production angle is recorded by the VTR associated

Fig. 3. Interior of CBS Studio Center trailer, showing production equip Fig. 2. CBS Studio Center trailer (exterior right side view). ment.

762 S M P T E Journal November 1978 Volume 87

Fig. 4. Post-Production Center within the CRS Studio Center trailer. Fig. 5. Close-up of the trailer Post-Production Center.

with it, no video control room or switchcr lefthand monitor shows the playback of the through capstan control commands that is required. The director remains on stage. record VTR. The editing control panel is force time-code differences to x r o . shooting complete scencs of sevcral min- on the left of the console, and a single set of The scenc is then edited in rcal time via utes in length in front of a live audience, VTR transport controls. including time- thc two-row switchcr to the left of the op- just as hc would have done using film codc displays, is shown on the extreme crator, as shown in Fig. 5 . canicras. right. The helical VTR synchronizer con- I f a n editing crror is madc at any time trols are centered betwecn them. during the sccne, the machines may be re- Multi-Camera “Film” System cued to a point just before the error, and The trailer unit is shown in Fig. 2. This cditing continucd from the last good cut. Helical VTR Synchronizer In vehiclc can bc movcd betwecn film sound fact, it is possible (with care) to rcpair even stages to servicc various productions as To make an intermediate cdit copy one bad cut in the middlc of a scenc. required. Thc production cquipmcnt is at through post-production editing, a mcans Onc thing is ccrtain: thc talent can be thc rear of the trailcr, as shown in Fig. 3. for kccping up to five helical VTRs in countcd upon to give exactly the samc Four complete channels are shown, each lock-step had to be devised. pcrformancc each time the scenc is re- consisting of a camcra and a videotape rc- The design of the VTR synchroniscr il- played! corder. The fifth V T K is installcd for later lustrates the versatility of a computer- I t was stated earlier that the intcrmcdi- usc in editing. compatible command structure. The Sony atc edit copy is csscntially the same as After some cxperimcntation, the pro- BVti- 1000 uses three digital control buses would bc produced from a pcrformancc duction company settlcd into three-camera and one analog control bus. One digital bus switchcd in a vidco control room. In fact, sccne covcragc, a well cstablished practice carries 200-kH7 clock pulses. The second it is better because no switching crrors nccd in film sit-coms. This technique places thc bus carries a serial 64-bit word with 32 bits be corrcctcd later. master, or wide-angle, camcra at center for command and 32 bits for status. The As with normal TV switchcd in a control stage, with anothcr canicra o n cach side third interleaves thc output of two internal room, final editing (including asscmbly of shooting the reverse angles. A fourth registcrs - one for SMPTE timc code and scencs, insertion of pick-ups, and titling) camcra is used infrequently for party the other for the mechanical tape counter. arc completed in an on-line editing facili- scenes or to carry the action through a Thc analog bus carries a continuously t Y . difficult move. variablc dc-voltage capstan ovcrride con- During shooting, the fifth VTR was used trol which is acted upon only i n thc pres- to doublc-record the master angle. Idcnti- ence of the capstan ovcrridc digital com- Conclusion cal SMPTE time codc is rcquircd o n all mand. The new I-in helical VTRs offer thc machines, and serves during editing a s the Typically, a scene would bc edited as system design cngineer a versatile new equivalent of a crystal black tapc with follows: the rnatcrial is first reviewed, component that is small and lightwcight prerecorded color black signal. This re- usually by playing the wide-angle VTR at and attractive in terms of powcr con- cording also provided protection for the the top of the scenc. Depressing the sumption, tapc consumption, and operating master camera angle - but, in the 25 cp- MARK button stores the %-point” frame cost. Picture and audio quality arc qua1 to, isodes recorded thus far, wc have not ex- code in a refercnce register. and in many ways better than, their ante- pericnced a record failurc. When it is time to post-edit the scene, cedents. The system just describcd would Aftcr production has bcen complcted, the CUE button is pushed, sending all not have been feasible without them. Pur- the next step in thc process is to producc an machines to the reference time codc. This ther, these new machincs, along with their intermediate cdit through post-production is donc by comparing each individual VTR portablc versions, are likcly to widen the editing. This rccording is esscntially the tinic-code digital bus with the reference usc of videotape for entertainment pro- samc videotape that would have resultcd if register and automatically issuing a scries grams previously produced on film, and to the sccnes had been switched in a video of commands forcing the difference to zero. broaden ENG applications to include control room during a livc television pro- When thc difference is zero, the “still documentaries. Perhaps even more signif- duction. framc” command is issued. icantly, thcy may cause the television plant The post-production editing booth is From this point all the machines respond engineer to question the large cxpenditures located in the rear of the trailer, :IS shown to a single set of transport controls as if he has been making in multi-level routing in Fig. 4. Thc lower four monitors show the they were one machine. When the PLAY switchers in large plants and reconsider the four-camera videotapes and the top center button is presscd, all machines start and are possibility of dedicating videotape re- monitor, thc edited output. The uppcr slewed into frame coincidcnce. This is donc corders to studios.

C‘orrnolly: Vidcofupi,P rogram Production 763