SMPTE Type C Helical-Scan Recording Format By DAVID K. FIBUSH

About two years ago there was little prospect that a 1-in helical-scan videotape recorded marily to eliminate the need to review all on one manufacturer’s machine could ever be played back on another manufacturer’s aspects of the format each time a change VTR. In a single year, however, this situation has changed and the S M P T E Standards is made. Typically, the format documents Committee has approved the basic format documents for high-quality I-in helical-scan include a document showing record loca- VTRs capable of interchanging tapes. Topics covered in detail in the paper include: the tions on the tape, a mechanical configura- process of developing a standard, with a list of the relevant ANSI and S M P T E tion document, and a number of electrical documents; helical video format parameters, with definitions and criteria for their parameter documcnts for video, audio, selection; location of tape tracks; video and sync records, with sources and magnitudes control track, ctc. Many pcoplc are famil- of various time-base errors; limitation of vertical-interval dropout; the requirement for iar with the record location drawing as this six heads; the contraints of video track straightness and longitudinal track dimensions; information is widely publicized to show audio and control-track recording; and video signal processing. I t is expected that the the users the available channels and some new SMPTE Type C format will provide a practical solution to the users’ requirements of the features of the VTR. This drawing for tape interchange. for the Type C format is shown in Fig. 1 and contains information that is part of C98.19. Each Type C document is listed by Introduction ferent manufacturers. However, early in ANSI number or SMPTE Rccommcndcd In an amazingly short period of time, 1978 preliminary interchange tapes were Practice number and title later in this scc- SMPTE committees have reached agrcc- exchanged with excellent rcsults. tion. Reference to format documents will ment on a proposed tapc recording format Development of a Standard be by these numbers. for high-quality 1- in helical-scan videotapc Duc to the electromechanical nature of recorders. Starting in January 1977 with Writing a standard proceeds in a num- ber of well defined steps. First, a Working VTRs, it is necessary to specify certain tape a “white paper” submitted to the SMPTE transport and video head scanning system by ABC and CBS, and ending with ap- Group is formed to work out the technical details and draft the various documents paramcters in ordcr to guarantcc good tapc proval by the SMPTE Standards Com- interchange. Ideally, accurate record lo- mittee, the basic format documents for that define, in this caw, a tapc format. The draft is next modificd and approved by the cations on tapc could be specified to clim- 525-linc NTSC systems have becn com- inate the need for specification of VTR pleted in less than one calendar year. parent engineeringcomrnittee (donc for thc Type C format by thc SMPTE Committee mechanical paramcters. However, due to With major improvements in quality and limitations on measurement riccuracy and on Video Recording and Reproduction the resulting expanded use of I-in helical the mechanical properties of tape, this VTRs, it was clear that a common format Technology on 7 December 1977). After the SMPTE Standards Committee ap- approach is not fcasiblc. The mechanical was needed if the users’ demands for tape pararncters and some basic system con- proves the documents (as they did, in this interchange were to bc satisfied. Through cepts are contained in C98.19. organizations such as the SMPTE. tech- case, also in December 1977), it becomes listed below arc thc Typc C format nical experts can work together to produce possible for the first time to distribute the documents that were complete by thc cnd a format standard of sufficient merit to proposed format documents to all intcr- of 1977. These were published in the serve major portions of the nccds of ested partics. This is done formally in the S M P T E Journal of March 1978 and arc cquipment users and manufacturers. This SMPTE Journal. whcrc comments are presently available from SMPTE Head- is exactly what is happening with the Type solicited.* After a reasonable timc for quarters. C format, whcrc major users were intcr- comment, the SMPTE Board of Governors ANSI C‘9R.IX: Draft American Na- ested in the features of formats charac- votes to approve or disapprove the format tional Standard Basic System and Trans- teristic of VTR equipment of various documents as SMPTE Recommended port Geometry Paramctcrs for Onc-Inch manufacturers. An SMPTE Working Practices or - for those considered lcast Group of technical experts sponsored by a likely to changc - to send them on to the Type C Helical-Scan Video Tape Re- corders. wide variety of VTR users and manufac- American National Standards Institute for turers worked out the technical details of possible approval as ANSI Standards. ANSI C‘98.19: Draft American Na- tional Standard Dimensions and Locations a format utilizing thc best features of scv- Where appropriate, approved documcnts of Records on One-Inch Typc C Hclical- era1 VTR manufacturers’ formats. The are sent to the IEC or IS0 as U S . docu- Scan Video Tape Recordings. new Type C format promises to be impor- ments to be considered for international ANSI C‘Y8.20: Draft American Na- tant to the interchange of vidcotapc pro- standardization. tional Standard Frequency Responsc and grams in the next ten ycars. Already, sev- At each step in the path towards stan- eral manufacturers are planning to build dardization, all negative tcchnical or edi- Refercncc Level of Audio Records for VTRs to the new format, and acceptance torial comments are Considered and, whcrc One-Inch Type C tlclical-Scan Video by users is tremendous. appropriate, alterations are made to the Tapc Rccorders. Approval of the Type C format as for- documents. Standards and Recommcndcd S M P T E RP 85: Proposed SMPTE mal Standards and Rccomrnended Prac- Practices arc automatically reviewed every Recommended Practice Specifications tices by the Amcrican National Standards five years, but important changes may be Tracking Control Rccord for One-Inch Typc C Helical-Scan Video Tapc Rc- Institute and SMPTE respectively is pro- incorporated as soon as they are identified. ceeding in a timely manner. As of the end As cxperience is gained with any new for- cordi ngs. of 1977, no programs had yet been inter- mat, it is quite possible that amendmcnts S M P T E RP 86: Proposed SMPTE changed between machines built by dif- will be needed in thc carly years of its use. Recomnicndcd Practice Video Reference This was true with the quadruplcx format, Carrier Prequcncics and Pre-emphasis Prc\cnlcd on 3 February 1 Y 7 X a t thc 12th Annual in which minor changes are bcing made Characteristics for One-Inch Type C He- SMPTE Television Conference in Allanla by David K. cvcn today. lical-Scan Video Tape Recordings. Fibusti. Ampcx Corp.. 401 Hroadwny. Redwood City. A number of separate documcnts are SMPTE Working Groups are presently CA 94063. Copyright GI by the Society of Motion Picture and Television Engineers. Inc. Previously used to define a videotapc format, pri- developing draft standards and rccom- publishcd in uncdited form in the SMPTE book Onc- mended practiccs for tape, reels, test ma- Iiwh Helical Video Recording. * See pp. I62 168 in the March I Y 7 X Jourtral terials and time-code recording.

-TAPE MOTION -TAPE MOTION AUDIO 2-0.8 0.8 AUDIO I 0.8 DROPOUT 0.4 17 t

V I D E O RISE 24.4 'i' 7 3 .? TAPE TRAVEL DURINQ O N E FIELD

~ ~~ ____ - TAPE REFERENCE EDGE J" 0.1 NOTE ALL LDIMENSIONS I N MILLIMETERS Fig. 3. Video track parameters. (NOT TO SCALE) Fig. 1. Record locations and dimensions for Type C format videotape. Drawing is not to scale; linear dimensions are in millimeters; and values are H O R I Z O N T A L SYNC nominal, to nearest 0.1 mm. P U L S E RECORD

UPPER DRUM

VIDEO TIP

LOWER DRUM TAPE REFERENCE EDGE TAPE ENTRANCE/ (QUIDED EDGE) GUIDE Fig. 2. Configuration of Type C scanner. Fig. 4. Sync pulse line-up.

Helical Video Format Parameters the tape with the tape under normal ten- the sync pulse alignment error be very close A complete description of the video sion. to zero to insure minimum phase jump in portion of a helical-scan tape format in- Effective drum diameter (D):A value H-sync pulse timing between tracks during volves many interrelated geometric pa- of drum diameter used in format calcula- still-frame operation. This restriction rameters. These parameters and other tions to take into account tip projection and provides the best possible slow-motion important itcms are dcfined below. air film (if any). The effective value is picture without special accessories and Scanner: A mechanical assembly con- typically equal to or greater than the actual eases design of special slow-motion ac- taining a drum, rotating pole tips, and value by 0.004%. cessories which are required for further tape-guiding elements. Writing speed (oh): The relative video improvement in performance. These spe- Drum: A cylindrical column around pole tip-to-tape speed. cial accessories, working in conjunction which tape is at lcast partially wrapped in Sync pulse alignment error (L,$):T he with an appropriately designed time-base order to form the head-to-tape intcrface of distance along a video track between a corrector, can provide an output signal a videotape recording system. video sync pulse record and the perpen- which meets FCC broadcast standards. Upper drum: That part of the drum dicular projection of a video sync record on The sync pulse line-up requirement is which does not contact the reference edge an adjacent track (see Fig. 4). shown in Fig. 4. Note that due to the odd of the tape (see Fig. 2). The upper drum is Track pitch ( P ) : The centerline-to- number of lines in a frame thecritical dis- sometimes designed to rotate in synchro- centerline distance betwcen two adjacent tance is an integer number plus one-half a nism with the video pole tips. tracks, measured perpendicularly to the line (2.5 is used for 525-line and 3.5 for Lower drum: That part of the drum tracks. 625-line systems). which contacts the reference edge of the Track width (W):T he width of the re- Because of the sync pulse line-up con- tape and usually contains guiding ele- corded track. straint, the desirability of simple geometric ments. Tape travel for onefield (Lf):T he dis- formulas, and the existence of established Vertical interval dropout: That part of tance the tape travels during the time of television scanning rates, the continuous- a television field not recorded by the video one television field. field format designer has a limited choice pole tip due to the tape being wrapped Continuous-field recording in the Type of parameters compared to a segmented- around the drum less than 360'. C format is accomplished by wrapping the scan system designer. Consider, for ex- Video rise (V,,):T he tape width occu- videotape nearly all the way around the ample, the following list of important video pied by a video track formed by wrapping drum, as shown in Fig. 2. For each com- parameters: tape n degrees around the drum. V360.i n- plete revolution of the video tip all active I . Sync pulse line-up number dicating a full 360° wrap, is needed in some television lines in one field are recorded in 2. Video rise calculations, whereas V346 is the actual addition to part of the vertical sync inter- 3. Writing speed video rise seen on the tape record for a val. The vertical interval dropout occurs 4. Drum diameter 10-TV-line vertical interval dropout or due to the fact that there is only 346' of 5. Tapespeed 252.5-tine video track (see Fig. 3). tape wrap around the drum to allow for 6. Track pitch Head travel (Lh): The distancc the pole tape threading and placement of the en- 7. Track angle tip travels in one complete drum rotation trance and exit guides. 8. Helix angle (corresponds to V360). Figure 3 shows the geometric relation The sync pulse line-up number is perhaps Track length (L,):L ength of the actual between track length, track angle, helix more fundamental than the others because recorded track with the tape under normal angle, tape speed, video rise and the vertical it provides a quantifying constraint on tension (corresponds to V346). interval dropout. A major constraint in other parameters such as track angle. Se- Track angle (&): The angle of the video calculating the values of thc various gco- lection of any two other parameters in ad- record with respect to the reference edge of metric parameters is the requirement that dition to this one will determine the rcst,

756 S M P T E Journal Nooemher 1978 Volume 87

and it is important that thc choice of the Table 1. Causes and magnitudes of time-base errors. three be prudent so that systems optimi- v to s s to v zation of all the parameters will be Source Interchange switch switch achicvcd. of error error range (w) (w) Typically the thrcc parameters chosen by the format dcsigner will be video rise as Drum diamctcr f0.012 m m 2.1 0.2 limited by simultaneous uses of the tape for Helix angle fo.0ooso audio and other signals; writing speed, for Sync lead location f0.004” 0.4 0.4 Thermal expansion f l I O C I .4 0. I this strongly affects video quality and tape (incl. self-compensating effects) consumption; and, as noted above, the sync Hygroscopic expansion &20%R .H. 6.1 0.6 pulse linc-up number. This determines tape Tape stretch f 0 . 2 newtons I .6 0.2 speed and, hence, tape consumption. The sync pulse line-up number can only be in- teger-and-one-half values; thercforc, its vertical interval dropout is optionally re- errors bccomc important to signal-system selection is critical to overall format per- corded as the sync record by a scparate and time-base-corrector designers. The formance. rotating video tip. sync-to-video switch causes a smaller error Values for the Typc C format were The control track is locatcd between the than thc vidco-to-sync switch because the chosen for convcnience to make tape speed video and sync records. Small guard bands vcrtical sync interval represents a 30’ dis- and track angle come out as relativcly are used on each side of the control track placement around the drum, while the simple numbers. Nominal values for the because it is easy to maintain magnetic and video interval represents a 330’ displace- Typc C format arc: electronic separation between the low- ment. Typical time-base-error causes and Tape speed 244.00 mm/s frequency saturatcd control track and the magnitudes are listed in Table I. Track anglc 2’34’00” high-frequency FM video information. A These step errors are for the “worst Sync pulse line-up 2.5 lincs third audio track is locatcd near the refer- case” interchange with a moderate envi- Vidco rise (346’) 18.525 mm ence edge of thc tape; it is of the same size ronmental range and maximum tolerance Writing speed 25.596 m/s as the first two and thus pcrmits similar of format parameters. In a typical casc of Effcctive drum 134.634 mm quality to be obtaincd. When time code is tape interchange, each source of error will diameter used, it is rccorded on the audio-3 track. tend to be smaller and there will be some Hclix angle 2’ 35 ‘29” cancellation between error sources. A Track pitch 0. I823 mm Video and Sync Records typical value for video-to-sync switch is 2.5 Track width 0.130 mm When the optional sync channel is re- p s and for sync-to-video switch, 0.3 ps. Some of these values do not appear in corded, the Type C format becomes a It is worth noting that even a “worst the draft format documents ANSI C98.18 “segmented-scan’’ format. However, since casc” total time-base step error represents and C98.19 bccause, typically, standards the switch points are well within the verti- only a very small change in record-to-play are written to contain only necessary in- cal interval, the active part of each field is track alignment or “interchange.” As an formation (in thc Type C format, that recorded in a continuous manner allowing example, a 10-ps video-to-sync switch error which is necessary to insure interchange of significant multi-speed features. As in any corresponds to a 10% track-to-track tapes). Such things as writing speed and segmented-scan system, there are inter- alignment error which, when properly track pitch become calculated values which change time-base errors associated with centered, is a 0.5-dBm odulation of the R F will be exactly the same on all VTRs if the switching between scanned tracks. These cnvclopc. publishcd standards are met. time-base errors cause no significant problem since they can occur during un- Vertical Interval Dropout Type C Tape Usage used times of the vertical interval. How- The location and size of the vertical in- As can be seen in Fig. 1, there are six ever, as more video signal “real estate” is terval dropout are an important part of the separate recordings that can be includcd on used (e.g., lines 13, 14. and 1 9 , t hese step Type C format, because correct selection a Type C format tape. There are two audio ’ tracks at the top edge of the tape with suf- R E C O R D TRACK 7 ficient separation to bc used as independent channels. A major portion of the tape is used by the video record which contains all active lines plus enough vertical sync in- formation for VTR operation. Information lost in thc main video channel due to the

FIELD I OR 3 - V l T S I E LEV AT I0 N DROPOUTS ALIGNED‘\ TOLERANCE 0.06 I II i i 1 II I I 1 1 I , {VIDEO TRACK n NOMINAL 10 H VIDEO TRACK nti DROPOUT

END OF I START OF VIDEO VIDEO 3I I :

NOTE: A L L DIMENSIONS 0.06 IN MILLIMETERS (SHOWN AT ONE EXTREME OF RANGE) Fig. 6. Vertical interval dropout growth due to interchange Fig. 5. Vertical interval dropout timing. elevation tolerance.

Fihush: Type C Recording Formal 757

TIP ROTATION NOMINAL TRACK EDGE 7 \r

PLAYBACK (CONFIDENCE )

STRAIGHTNESS LIMITS

NOTE: ALL DIMENSIONS SYNC VIDEO , I N MILLIMETERS Fig. 7. Video and sync tip locations. Fig. 8. Video track straightness. of these values is necessary both to permit conditions could not be assured in practical Video Track Straightness VTR operation without the optional sync interchange situations. Good tape interchange on any VTR is channel and to allow a time-basc corrector Why Six Heads? strongly dependent on track straightness. to produce signals meeting FCC broadcast This is particularly true when the track is standards during slow-motion or still-frame Actually, a compatible Typc C format 41 1 mm long as in the Type C format. operation. Figure 5 shows a timing di- tape can be recorded and played on a VTR Track straightness is dependent on many agram of the vertical interval dropout with only one operational rotating video tip. factors: entrance and exit guide placement; based on the tolerances given in C9X.18 Unfortunately, as a tip starts and ends method of tape guiding around the drum; and C98.19. The shaded areas represent contact with the tapc, it creates longitudi- tapc tension build-up around the drum; dropout growth that can occur on inter- nal disturbances in the tape that travel tape slitting characteristics; and others. change playback due to other format tol- around the drum. These tip disturbances, The specification for track straightness in erances. A contributor to interchange in turn, create time-base errors which have the Type C format requires that the edge dropout growth is the amount of track- a tendency to cancel on playback if the of the video track be contained within two to-tape-edge error allowed by C98.19. This record and playback machines have tips in parallel straight lines 0.030 mm apart. As error is eliminated in terms of playback the same location on the drum. Without can be seen in Fig. 8, this specification in- signal quality by adjusting the tracking as this cancellation, it is difficult for a time- sures that adjacent track edges are sepa- shown in Fig. 6, with a resulting increase base corrector to eliminate the “velocity” rated by at least 0.022 mm under “worst in playback vertical interval dropout of 53 effects and visible picture defects result. I n case” interchange conditions. ps or nearly one television line. order to reduce this problem, the Type C In terms of format documents, the video During operation at speeds slower than format requires that nonoperational tips be track (record) straightness is specified in play speed, the vertical interval dropout placed in “unused” locations with toler- ANSI C98.19 since this is measured on the grows by as much as 2.5 horizontal lines, ances for minimizing velocity errors. recorded tape, while recommended VTR with the maximum occurring when the The locations of the six tips around the mechanical parameters are specified in tape is stopped. This 2.5H is exactly the drum are shown in Fig. 7. For complete C98.18. There are a number of design sync pulse line-up value, since tape motion location information with tolerances. see methods using slightly different mechani- is not contributing to relative tip-to-tape ANSI C98.18. Four allowed format fea- cal parameter values which would result in travel. Location of the 2.5H depends on tures lead to the logical conclusion that six good video track straightness and angle, tapc longitudinal position with respect to heads are required. The four are: ( I ) re- and thus permit reliable tape interchange. the drum and will cycle from start-of-video cording of sync in addition to video; (2) For that reason, section 6.0 of C98.18 was to end-of-video at slow tape speeds. A insert edits using flying erase; (3) confi- written as one recommended method of “worst case” placement of the 2 . 5 H in- dence playback during record; and (4) obtaining the desired results. Interchange crease is shown in Fig. 5. separate record/play heads to allow tip of tapes made on VTRs from different design optimization. Starting with one manufacturers is the final test. Exchange From a mechanical standpoint, it is dc- record/play video tip, add a record/play sirable to keep the vertical interval dropout of tapes is being supervised by the Heli- sync tip plus two erase tips for a subtotal of cal-Recording Subcommittee of the as large as possible for ease of threading four. Video Confidence playback during SMPTE Committee on Video Recording and reliability in terms of guide pin-to-pin record is considered an extremely impor- and pin-to-drum spacing. The nominal and Reproduction Technology. Eight tant feature by many users, so add one companies representing manufacturers and Typc C vertical interval dropout is 10 more tip. Finally, since there are now sep- users are involved in the preliminary ex- horizontal lines from start of line 5 to the arate record and play tips for the video change of interchange tapes. Results to start of line 15 in fields 1 or 1 1 1 , with ap- channel, performance improvements are date are excellent, with one exchange of propriatc similar locations in fields I I or possible if each tip design is optimized for tapes in March and a second in August IV. its purpose. To utilize this advantage, it is 1978. Line 15 was selected for the start-of- necessary to rotate the drum phase by 120’ video in order to insure that the video on playback with respect to record. In order channel can be used for rccovcry of the to play back the sync channel, it is neces- Longitudinal Track Dimensions vertical interval test signal (VITS) i n all sary to add a playback (confidence) head Record/play gaps of heads for all lon- playback interchange conditions. Line 5 in the sync channel, and this last gives a gitudinal tracks are placed 102.0 f 0.4 mm was selected for the end-of-video in order total of six tips. It should be emphasized downstream of the start-of-video (reference to insure that one or more equalizing pulses that any number of these tips, up to five, ANSI C98.19). Because the control track would be available to act as vertical sync can be replaced by high-reliability, low- head is included in this group, longitudinal during slow/stop motion when the optional cost, nonoperational tips depending on the adjustment of the head stack is normally sync channel is not available. With any features desired in a fully compatible Type used in order to achieve the relatively tight larger nominal dropout size these limiting C format VTK. “lip-sync’’ tolerance. A result is that when

758 SMPTB Jourrrul N o ~ c ~ l h eIYr7 X V o l r i t w 87

time codc is recorded on the audio-3 Tahle 11. Build-up of tolerances from the reference edge of the tape to the audio-l channel. channcl, the “worst case” intcrchangc timing error of time codc/video on play- Mnxinium tolerance back will be 3.3 ms, or about one-fifth of a Source of tolcrancc range (mm) field. Calculation of “worst casc’’ timing Location of tapc guidc with respect to rcfercncc surface 0.050 errors for five widely uscd formats givcs the Length of tape guide with rcspcct to nominal tapc width 0.05 I Minimum width of tape with rcspcct to nominal tapc width 0.025 - following rcsults Type A I-in helical, I.ocation of recording hcad with respect to rcfcrcncc surface 0.070 13.0 ms; Type B I -in helical, 4. I ms; Typc (one of four lcads in the stack) C 1 -in helical, 3.3 ms; 2-in quadruplcx at Width of recording hcad + 0.050 I5 in/s, 6.7 ms; 2-in quadruplex at 7‘/2 in/s, Total tolerance to top of I st audio track: 0.246 13.3 nis. None of thesc timing errors arc standard for original recordings inasmuch as thc Figure 9 shows the resulting “worst Frequency rcsponse is controllcd by American National Standard Time and casc” interchange ovcrlap of audio- I tracks specifying the ratio of short-circuit tape Control Code (ANSI C98.12) rcquires a which rcprcscnts a maximum 2.9-dB lcvcl flux level to frcqucncy, with a low-fre- timing accuracy of two horizontal lincs, or variation. Typical intcrchangc will, of qucncy boost 3-dB point at 50 Hz and a 0.13 ms. I n many systems applications, course, be much bcttcr than these fig- high-frequency roll-off 3-dB point at 10610 video synchronized regcncration of off-tape ures. Hz. Thcsc 3-dB points correspond to time code is uscd to eliminatc this error. playback equalization of 3 180 ps and 15 Dimensioning of each longitudinal track ps. cdgc is with rcspcct to the rcfcrcnce edgc Audio Recording Audio-I was chosen to be the sccond of the tapc. This allows a freedom of dcsign track from the edgc of the tape bccausc approach in terms of adjustment or prcci- The Type C format for audio rccording there it is best protected from edge dam- sion machining mcthods. Valucs were (ANSI C98.20) is very similar to the cor- age; this is important because it is uscd for chosen to allow reasonablc, and thercforc responding documcnts for other VTR for- the primary program audio channel. Stereo economical, tolcrances on all parts af- mats. All recordings on the three audio audio is recorded with the sum channcl on fccting track location. Two important tracks will be niadc by the anhystcrcsis audio-l and the diffcrcncc channel on factors considered wcre, first, that there are (bias) method unless cxccptions arc defincd audio-2. Phasing of the recordings on four heads that must meet tolerances si- by other SMPTE Recommended Practices audio-I and audio-2 tracks is such that, if multaneously and, sccond, that tape should or ANSI Standards. reproduccd with a head widc cnough to not be forced against the referencc cdge. A refcrcnce level of 100 nWb/m has cover both tracks, the flux levels would be Thc reliability of forced edgc guiding is been chosen to match the recording char- additive. As noted, when time and control highly dcpendent on the mechanical acteristics of 1 -in helical-scan tape avail- code is uscd, it is recorded on the audio-3 propqties of tapc and should not be rc- able in 1977. Thc reference lcvcl (corre- track. quircd by the format for the low guide- sponding to 0 vu) is choscn so that a record wrap-angle longitudinal hcad arca. level 8 dB above the refercncc lcvcl will Build-up of tolcrances in a typical tapc producc lcss than 3% distortion without the Control Track Recording transport, uscd to dcterminc thc upper edgc use of prcdistortion techniyucs. Predis- of the first audio channel, might be as listcd tortion is allowed but is not part of the Typc The control track rccord consists of a in Table I I . C format. series of saturated flux levels alternating in

NOMINAL 0.8 WORST CASE 0.575 -TAPE MOTION HEAD GAP \ CENTERLINE I T I T T I 231725 I \ cr+ I NOMINAL VALUES MINIMUM VALUES MAXIMUM VALUES L - S - 4 (REF V16.22/4)

FIELD I VIDEO TIP

NOTE: ALL DIMENSIONS TAPE REFERENCE EDGE C T S*N IN- IN MILLIMETERS I Fig. 9. Audio-l track dimensions.

FRAME A (EVEN) FRAME B (ODD) 1- 1-

B J 4 * 0 8 M S

S L N I I -L] L O 4 t O 6 M S I RISE AND FALL TIMES NOT TO SCALE 0 015 2 0.01 U S Fig. 10. Tracking control waveform and timing. Fig. 11. Control track flux polarity.

Fihush: Type C liecording Fornrar 759

VIDEO BURST RECORD I CURRENT TO roll-off spccified as a one-time-constant PREEMPHASIS MODULATOR low-pass filter with -3-dB point at 6 SYNC HEADS MHz. Fig. 12. Video signal processing. Conclusion polarity at a field rate as shown in Fig. 10. Video Recording Experts from all segments of the VTR An extra pair of transitions is added on Signal processing of the recorded video industry, as members of the SMPTE alternate frames to aid in color frame of the Type C format is similar to the Working Group on Continuous-Field identification. Since the recording is satu- high-band of quadruplex recordings, ex- One-Inch Helical-Scan Magnetic Re- rated, it can be rccorded at a level that will cept that burst amplitude is increased by 6 cording, have, in less than one year, com- erase previous recordings, thus climinating dB on record and reduced to normal on pleted work on the Type C I-in helical-scan the need for an erase head. playback. A block diagram of thc signal videotape recording format. Selection of Alternatc frame pulses which are always processing system specified by SMPTE RP the Type C format characteristics and present in the control track recording may 86 is shown in Fig. 12. Any other signal parameters was governed by the users’ be optionally used to identify specific color processing system that produces the same specifications of information to be recorded frames. This use of the altcrnate frame result is considered to meet the intent of the and by interchange requirements. Al- pulses is optional for some practical sys- format; for example, the order of burst though this is a new format, the experience tems reasons. Proposed EIA Standard amplification and preemphasis could bc gained by more than fifteen years of suc- RS-10714 specifies the timing relation of interchanged. cessful continuous-field helical-scan re- burst to horizontal sync so that color Amplification of the burst with respect cording with various similar formats, frames may be identified on signals meet- to its normal levcl provides a 6-dB S N R coupled with sound engineering practice by ing the standard. The first problem is that improvement of the reproduced burst, manufacturers, will undoubtedly prove the many signals will not meet thc EIA Stan- which improves the accuracy of time-base selection of the SMPTE Type C format to dard, SO that color frame identification correction. Amplitude and phase of the be a practical solution to the users’ de- becomes risky at best. Another problem burst are maintained to an accuracy of mands for tape interchange. occurs because many insert edits do not f O . l dB and * I 0 in the burst amplifier. need to be color framed, but if they are not Similar accuracies are expected on play- Discussion color framed, an edited tape would not back. Ken Hori (WGBH-TV):T he half-head obey an identification rule throughout the Preemphasis and modulation are iden- vertical interval head is an option for this tape. Nonetheless, when the alternate tical to the quadruplex high-band with the format. Yet the half-head track must rec- frame pulses are used for color frame following parameters: time constant t l = ord vertical sync information if the head is identification, in some editing systems it 240 ns; time constant 1 2 = 600 ns; peak equipped in the machine. It seems too will be advantageous to have a convention white frequency = 10.0 f 0.05 MHz; and binding on us for future expansion if this such as that defined by Fig. 10 and in the blanking frequency = 7.9 f 0.05 MHz. real estate with full-bandwidth recording proposed Type C format SMPTE R P 85. In order to obtain a particular ratio of capability is restricted to recording vertical Transitions of the control track signal rccorded flux level to frequency, current sync only and is not available for computer occur during the middle of each field since drive supplied to the video and sync heads control data, for example. I wonder if we this minimizes sensitivity to timing errors, is modified by the record amplifier. The may regret this decision in the future. and precise alignment of a transition need desired result is that the recorded chroma Mr. Fibush: SMPTE Recommended not match any particular part of the verti- sidebands have their amplitude, relative to Practices and ANSI Standards may be cal interval. Polarity of the transitions does the carrier, increased by about 2 dB (which revised at any time so we have not ruled out not necessarily have to be specified, as provides an equivalent increase in signal- other uses in the future. The SMPTE phase-insensitive detection circuits can be to-noise ratio). The record-amplifier fre- Working Groups felt that such optional designed; however, it seems best to do so in quency response required to obtain this uses would cause operational confusion at case of future requirements. Polarity of the result depends on the type of tip material this time. recorded flux is shown in Fig. 11. South used for the record head. If metal heads Bert H. Dam (Bell & Howell): Will the poles of magnetic domains are downstream made of sendust material (a silicon-alu- VPR-I replace the disk machines in ath- (shown to the left in Fig. 1 I ) of thc north minum-iron alloy) are used (as in many letic-event stop- and slow-motion appli- poles during the vertical interval identi- 2-in quadruplex recorders), a constant- cations? fying fields I and 111. Therefore, the current-vs-frequency drive produces the Mr. Fibush: The VPR- 1 has many of the north-to-south transition which occurs desired flux, due to high-frequency losses features of a slow-motion disk machine but during fields I I and IV will be adjacent in thc tip material. Since most Type C re- not the reverse motion capability. Flexi- south magnetic poles, that is, the transition corders are expected to use tips made of bility of operation and storage capacity area will attract the south-seeking pole of ferrite material, the recommended record may encourage its use in many applica- a bar magnet. amplifier response has a high-frequency tions.

760 S M P T E Journal Nooember 1978 Volume R7