Analog Vtr

Training Material NHK-CTI 2007 JICA Engineering Course Aug.20.’07

Analog VTR

JAPAN BROADCASTING CORPORATION Broadcast Master Control & Engineering Division Broadcast Engineering Department

Shiho Morooka

Training Material NHK-CTI 2007 JICA Engineering Course

Analog VTR 1 History 2 Basic Mechanism 3 βcam

Training Material NHK-CTI 2007 JICA Engineering Course

1. History 1-1 Development of VTR 1-2 Typical types of VTRs used in NHK

Training Material NHK-CTI 2007 JICA Engineering Course

1-1 Development of VTR （ Composite ）

Hi Hi--Vision VTR Helical 1inch

2inch-4head (1956)

(1976)

D-2

D-3

D-5

(1987)

(1990)

(1993)

HD D-5 (1996)

D-1 (1986)

βcamSX

（ Component Component） ）

Mpeg-IMX

(1995)

βcam

Digital βcam

βcamSP

(1981)

(2000)

(1986)

HDCAM

(1993)

U matic

HDCAM SR

(1998)

(2003)

DVCAM

(1970)

(1996)

MⅡ Ⅱ (1986)

DVCPRO

DVCPRO50

(1995)

DVCPRO HD

(1998)

DVCPRO HD-LP

(2000)

DVC

Consumer--use Consumer

(1993)

β (1975)

VHS (1976)

8mm (1982)

EDβ (1987)

S-VHS

Digital VHS (1999)

W-VHS

(1993)

(1987)

Hi-8 (1988)

Digital ＶＴＲ

(2002)

Training Material NHK-CTI 2007 JICA Engineering Course

1-2 Typical types of VTRs used in NHK

D3VTR

HDD5VTR

βcamVTR

HDcamVTR

Training Material NHK-CTI 2007 JICA Engineering Course

2. Basic Mechanism 2 -1 2 -2 2 -3 2-4 2 -5 2 -6 2 -7

Magnetic Recording Head & Tape Helical Scan βcam VTR Rotating Drum’ Drum’s Head Trouble Tape Tracking

Training Material NHK-CTI 2007 JICA Engineering Course

2-1 Magnetic Recording Current and Magnetic Field ・ An electric current in a coil of wire produces a magnetic field. ・ Any change in the magnetic field around a coil of wire will cause a voltage to be induced in the coil.

Magnetic field

Electric current

coil of wire

Training Material NHK-CTI 2007 JICA Engineering Course

2-1 Magnetic Recording signal current

Recording The signal current through the core of the head generates a magnetic field. The magnetic field creates a remnant magnetization on the tape.

the core of the head magnetic field

tape Remnant magnetization

Reproducing After remnant magnetization on the recorded-tape pass into the core of the head , the core of the head induce a voltage(a current) that is proportional to the remnant magnetization’s strength.

signal current

the core of the head magnetic field

tape Remnant magnetization

Training Material NHK-CTI 2007 JICA Engineering Course

2-2 Head & Tape VTR Head Head Gap(Front Gap)

Azimuth Angle An Enlargement of Head Gap

Structure of a Typical Head Design

An Enlargement of a Head

Training Material NHK-CTI 2007 JICA Engineering Course

2-2 Head & Tape Magnetic Tape Magnetic Powder

Binder

Magnetic Layer Under Layer

Analog VTR Tape for Broadcasting

Digital VTR Tape for Broadcasting

Magnetic Powder on the tape surface

Back Coating

Structure of Magnetic Tape

Training Material NHK-CTI 2007 JICA Engineering Course

2-3 Helical Scan The Tape Speed Problem The audio signal requires a bandwidth of about 20Hz to 20 KHz. The video signal requires ………

about 30Hz～ ～4.2MHz.(wider than audio)

The method of recording the video signal is • Speeding up the tape. • Reducing the gap width .

Erase Head Record Head

But even with the minimum narrow a gap, a tape speed of 2500 ～3800cm/s was needed to record full bandwidth video! The solution of the tape speed problem is……

Moving the head past the tape (Helical-Scan)

Audio Player Mechanism

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2-3 Helical Scan The HelicalHelical-Scan Principle

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2-3 Helical Scan The HelicalHelical-Scan Principle DRUM ROTATION DRUM

AUDIO R/P HEAD PINCH ROLLER

T-REEL

S-REEL

ERASE HEAD GUIDE POST VIDEO R/P HEAD

GUIDE POST

CAPSTAN CTL R/P HEAD

Physical Relationship between Heads and Tape

Training Material NHK-CTI 2007 JICA Engineering Course

2-4 βcam VTR βcam VTR Audio Head

Drum

Supply Reel

Full Body

Take-Up Reel

Inside from Top

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2-4 βcam VTR βcam VTR

Audio/TC erase Head CTL Head Full Erase Head Audio Conf. Head Around Drum

Capstan

Around Audio Head

Training Material NHK-CTI 2007 JICA Engineering Course

2-4 βcam VTR βcam VTR

Inside from Top

Inside from Right-Side

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2-5 Rotating Drum’ Drum’s Head βcam VTR (Play&Rec) (Play&Rec)

(Play&Rec) (Play&Rec)

Disposition of Heads View (Upper)

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2-5 Rotating Drum’ Drum’s Head Tape Recording Pattern ＣＵＥ Track Audio Track２ ２ Audio Track１ １

AnalogＶＴＲ ＶＴＲ

←Direction Of Tape Travel ＣＴＬ Track TimeCode Track ＣＵＥ Track

DigitalＶＴＲ ＶＴＲ

←Direction Of Tape Travel ＣＴＬTrack ＣＴＬ TimeCode Track

Training Material NHK-CTI 2007 JICA Engineering Course

2-5 Rotating Drum’ Drum’s Head Azimuth Recording Guard Band Recording

Head Motion

Guard Band

↑Head Gap

Azimuth Recording

θ： ：Azimuth Angle

Some Cross-Talks from a adjacent track are reduced by Azimuth effect.

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2-6 Troubled Tape

Lost tracks

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2-6 Troubled Tape

Damaged tracks

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2-7 Tracking Tracking & RFRF-Signal Big（ （Normal) Big ＲＦレベル大 ヘッド Head

On Track オントラック ＲＦ Level

Shifted Track トラッキングずれ

ＲＦレベル低下

Off Track オフトラック

Reduced

ＲＦ Level Small ＲＦレベル小

ＲＦ-Signal ＲＦ Relationship between Tracking and RF-Signal

Training Material NHK-CTI 2007 JICA Engineering Course

2-7 Tracking AutoAuto -Tracking The video playback head is mounted on a bimorph, which is made up of two thin flexible strips of a piezo-ceramic material bonded together. The strips bend when a voltage is applied across them, and they are mounted so that this causes the head to move at right angles to the recorded track.

Auto-Tracking by Play Head

Training Material NHK-CTI 2007 JICA Engineering Course

3. βcam 3-1 Outline 3-2 Typical Type 3-3 βcam SP 3-4 Function of the Cassette Plug and Tab 3-5 Tape Path 3-6 Rotating Drum’ Drum’s Head 3-7 Audio Head 3-8 Tape Pattern 3-9 Component Recording System 3-10 CTDM System

Training Material NHK-CTI 2007 JICA Engineering Course

3. βcam 3-11 3-12 3-13 3-14 3-15

Dynamic Tracking Maintenance Digital Hours Meter Adjustment Error Messages

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3-1 Outline Betacam VTR








１/２inch tape in cassette Analog components recording ＣＴＤＭ system Guard band-Azimuth recording (Auto Tracking Play Head) ＳＯＮＹ ＢＶＷ‐ ＢＶＷ‐７５

Training Material NHK-CTI 2007 JICA Engineering Course

3-1 Outline(Notes1) In 1970's, ENG began to become the main stream in the news covering , but 3/4 inch UmaticVTR was lack of mobility because of not being separated the video-engineer from the cameraman . Then we looked forward to the appearance of the combined camera with VTR. In 1981 , Sony announced Beta Cam format installed VTR with camera which was based on consumer Beta-VTR with a small body and a good quality of the video picture . A recording-speed to the tape is the same as being used fundamentally with the consumer-VTR, and for obtaining a high quality of the video more than Umatic-VTR, it is separated a color signal(C) from the luminance signal(Y) , and is adopted the format of the separate track with two Heads . When a NTSC composite signal is changed into the base band of the color differential signal R-Y and B-Y , Each signal becomes 1.5MHz and 0.5MHz. Beta Cam format increase that both frequency to 1.5MHz for emphasizing color character. And after the compression ,each color-differencial-signal is considered that includes 3MHz because those signals of 1.5MHz are compressed in the time-axis in two times. In 1987 ,Beta Cam SP (Superior Performance) appeared that performance was enhanced and developed for the studio-use as well. (Beta Cam was developed for ENG-use at first.)

Training Material NHK-CTI 2007 JICA Engineering Course

3-1 Outline(Notes2) Recording and Play Back(Reproduce) time was expanded into about 90 minutes, and the improvement of the quality of video and sound was achieved by utilizing of the metal video tape with a compatibility of the conventional Beta Cam. The Large-size cassette-tape was developed with thickness 25mm ,Length 254mm and width 145mm for recording more than 90 minutes. There is size of 2.5 times in comparison with the standard cassette . The track pattern of the Beta Cam SP is the same as conventional Beta Cam . Emphasized FM career by 1.3MHz with a metal-tape , and the frequency of the Luminance signal became 4.5MHz (-3dB) and SN ratio became more than 51dB. A CN ratio improves about 6dB with the metal video tape toward the usual oxidized-iron tape. And the deterioration of the video-quality by dubbing is decreased by this improvement of the signal characteristic as well. The video-quality of the 3rd generation of SP is equivalent to 1st generation of the usual format. FM-audio was introduced with SP. Dynamic-Range is beyond 85dB. Dolby-C is used for the the fixed audio Head as before. FM audio-signal is recorded in the Low frequency of FM-modulated Chrominance-signal with frequency-multiplexed.

Training Material NHK-CTI 2007 JICA Engineering Course

3-2 Typical Type SP DT PlayBack ONLY

BVW-10

BVW-60

BVW-65

Recording PlayBack

BVW-40

BVW-70

BVW-75

Training Material NHK-CTI 2007 JICA Engineering Course

3-3 BetaCam SP- Superior Performance (Notes1) 1. High quality pictures using metal particle tape Thanks to the usage of metal particle tape and the newly developed video head, “Beta Cam SP” offers a much higher video quality, compared to the original “Beta Cam” format, by improving signal-to-noise(S/N) ratio, frequency response, linear waveform distortion and fine reproduction characteristic. Owing to this improvement, the video quality is highly enhanced and is maintained even after multiple dubbings. The high durability of the metal particle tape meets professional standards, especially for the broadcasting of commercials. 2. 4 Audio channels In addition to the two conventional channels of longitudinal (LNG) audio, two channels of frequency modulated audio (AFM) are recorded on the chrominance track (only when metal particle tape is used). The wide dynamic range of the AFM audio enable the unit to handle any unexpected surge of the recording signal level. The metal particle tape also gives the LNG audio excellent frequency response and low distortion. 3. Longer recording and playing time The “Beta Cam SP” format allows a maximum of 100 minutes for recording and playback by utilizing a large cassette. In addition, the small(conventional) size cassette tape(maximum 35-minute) can be used.

Training Material NHK-CTI 2007 JICA Engineering Course

3-3 BetaCam SP- Superior Performance (Notes2) 4. Compatibility with conventional “Beta Cam” VTRs The BVW-70(P) automatically distinguishes the type and size of cassette tape, and performs the recording and playback with the appropriate format. Oxide cassette tapes recorded on a conventional VTR can be played back on the BVW-70(P). Metal cassette tapes recorded on the BVW-70(P) can be played back on conventional “BetaCam” format VTRs which has been modified a little.

Characteristics of Video

Characteristics of Audio

Training Material NHK-CTI 2007 JICA Engineering Course

3-4 Function of the Cassette Plug and Tab Oxide/Metal tape OPEN ： Metal tape CLOSE：Oxide tape S cassette MISS REC (for Oxide tape)

S cassette MISS REC (for Metal tape)

Reel hub diameter OPEN ： large CLOSE：small Back of a video cassette Video tape thickness OPEN ： thick(20μm) CLOSE：thin(15μm)

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3-5 Tape Path Audio Head Audio Head

Drum

Drum

Supply Reel

Take-Up Reel

Inside from Top

Supply Reel

Take-Up Reel

Training Material NHK-CTI 2007 JICA Engineering Course

3-6 Rotating Drum’ Drum’s Head (Play&Rec) DT Head

(Play&Rec)

C Y CH1 (Play)

(Play) Y DT Head CH2 C (Play&Rec)

(Play&Rec)

Heads View (Upper)

Heads View (Side)

Training Material NHK-CTI 2007 JICA Engineering Course

3-6 Rotating Drum’ Drum’s Head (Notes) Head Cylinder rotates 30rps. Two Luminance signal Heads and two color signal Heads are stuck to each of the upper cylinder for ch1 and ch2 symmetrically, And two more Erasing Heads are stuck. And also from Type of BVW-60, confidential Heads developed for checking the condition during recording ,then Type of BVW-65 and BVW-75 utilize AutoTracking Head as confidential Heads. The luminance and color signal are completely separated and are recorded as two component signals on each recording track . The video-quality was remarkably improved without mutual interference of the luminance and the color ,because of excluding color-subcareer signal. Though a Luminance signal and a color signal are recorded separately , R-Y and B-Y signals time-compressed by 1/2 are recorded in 1 scan-line alternately. The two audio signals are recorded on the top edge of the tape ,and a control (CTL) signal and a Time Code are recorded on the bottom edge, and they are used for editing . The track width of the Luminance signal and the Chrominance signal are both 73µm, and the track width between Y and C signal is 80.5µm . A tape speed is 118.6mm /s of about 6 times of consumer-Bata.

Training Material NHK-CTI 2007 JICA Engineering Course

3-7 Audio Head

Audio/TC Head Audio Full Erase(BVW-75) Audio/TC Rec Haed

Audio Conf Head

Capstan Drum Audio Confidence Head Blade

CTL Head Full Erase Head

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3-8 Tape Pattern

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3-9 Component Recording System Component Recording System Tape Video in

(composite)

Decoder CTDM

Frequency Modulator

Y C

Y Rec Amp

Component in R-Y B-Y Y

DUB in Y C

Video out

(composite) (component) Y R-Y B-Y

TBC

Frequency Demodulator

CTDM ： Compressed Time Division Multiplex

RF Equalizer

Head Amp

TBC ： Time Base Corrector

C

Training Material NHK-CTI 2007 JICA Engineering Course

3-9 Component Recording System(Notes) As the characteristics of Beta Cam’s recording system, it is to record three signals of Luminance signal, R-Y and the B-Y signal separately. After adding synchronous signal , Luminance signal is frequency-modulated after Emphasis and then it is recorded. Also only one Luminance signal uses one track. On the other hand , for recording two signals of R-Y and B-Y in one track,two signals are compressed with the time-axis in each of 1/2. Then, it is multiplexed in a 1H (line) period, and recorded in one track. This multiplex method is being called CTDM(Compressed Time Division Multiplexed Chrominance Signals). There are two audio channels and one control track, one Time Code track . Moreover, FM audio is multiplexed on the Chrominance signal for the hi-fi audio ,and it is recorded in the Chrominance signal track in Beta Cam SP(not usual Beta Cam). It's a way to reproduce Luminance signal ,demodulation and de-emphasis. Since R-Y and B-Y signals were compressed by 1/2 in the recording , then those signals are needed to be expanded two times one more by CCD-Memory for getting two the original separate signals (R-Y and B-Y signals).

Training Material NHK-CTI 2007 JICA Engineering Course

3-10 CTDM System CTDM : Compressed Time Division Multiplex

Process of CTDM (For Recording)

Process of CTDM Decoded (For reproduction)

Two CCD analog line memories are used for each color differential signals, they write data in a line , and that data are read in a next line at a half time of writing. There are here respectively two sets, and they are written and read in every line alternately. R-Y and B-Y signals are compressed and are expanded again on the time-axis. Therefore R-Y and B-Y signals are late against Y signal for 2 lines , and those signals need time-adjust during Play Back .

Training Material NHK-CTI 2007 JICA Engineering Course

3-10 CTDM Signal CTDM : Compressed Time Division Multiplex Luminance Signal

CTDM Signal

Two color difference signal R-Y and B-Y are compressed with time-axis by 1/2 , and those are collected in 1 scan line. A synchronous signal called a Beta-Cam-sync is added to the Luminance signal and color signal. The Beta-Cam-sync is bigger than the usual syncsignal generally being used. FM career is high-frequncy so that moire may not occur again. It becomes possible by this that it gets the syncsignal information for high SN ratio at the time of the Play Back and then relations between the Luminance signal and the chrominance signal can be maintained in the high precision.

Training Material NHK-CTI 2007 JICA Engineering Course

3-11 Dynamic Tracking Moving of Head with tape track Gap Head

Azimuth recording

Check H-SYNC Timing !

Y

Y

C

C

mistracking ! Y

Y

C

C

Y

Y

C

C mistracking !

time lag

time lag

Training Material NHK-CTI 2007 JICA Engineering Course

3-12 Maintenance ・General maintenance once four months ・A regular manufacturer Overhaul usually once a year General maintenance １．The confirmation of the Head use time. ２．Cleaning of the video/audio Head and the tape path. ３．Play Back check (with reference tape.） ） ・The confirmation of a degree of chrominance astringency with the color bar. ・The confirmation of the frequency characteristics with the multi-Burst. ・The confirmation of the tracking. ・The confirmation of the audio level and, the quality of sound with 1kHz. ４．Recording and Play Back check. ・Select the color bar and 1kHz of the test signal for the input signal, and adjust the input level with that test signal. ・Record that signal and reproduce that signal. Then, confirm whether there is a wrong point in the video and audio. ・Record the signal with 1kHz and 0VU, and reproduce that signal. Confirm it with the audio level, S/N, the wow flatter, and so on. ５．The confirmation of the basic movement of VTR. The confirmation of the movement and control such as Play Back, Recording, Forward and Rewind.

Training Material NHK-CTI 2007 JICA Engineering Course

3-13 Digital Hours Meter Time indicated ： We have to increase the number by ten.

T1 T2 T3 CT T1： T1： OPERATION Total time for turning on electricity T2： T2： DRUM RUNNING Total time for a drum rotating with tape threading T3： T3： TAPE RUNNING Total time for a drum rotating besides tape touching a drum in FF, REW, PLAY, SEARCH, REC or EDIT modes. CT： CT：THREADING Total number of times of tape threading and unthreading

Training Material NHK-CTI 2007 JICA Engineering Course

3-14 Adjustment Color Bar

Check levels of luminance signal and chrominance signal.

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3-14 :Adjustment Bowtie Signal

Check synchronization of luminance signal and chrominance signal.

Timing is matched.

Luminance signal is delayed for chrominance signal.

Chrominance signal is delayed for luminance signal.

Training Material NHK-CTI 2007 JICA Engineering Course

3-15 Error Messages Errors ErrorError-1：REEL TROUBLETROUBLE-1 When tape slacking is detected during unthreading or tape breaking is detected during threading, tape protection operation is done and this message is displayed. ErrorError-2：REEL TROUBLETROUBLE-2 When tape breaking is detected in REC, SEARCH, FF and REW modes, tape protection operation is done and this message is displayed. ErrorError-10： 10：Humid Displayed when humid condensation is detected. ErrorError-20： 20：CASSETTE COMPARTMENT MOTOR LOCK When cassette up/down operation is not completed, tape protection is done and this message is displayed.