Chapter 6

All About Videotape

Introduction

No video recording is possible without videotape. The technical quality of a finished production depends greatly on the quality of the videotape used. Old, worn or poor quality videotapecan produce a distorted picture or can even clogthe video heads, resulting in no recording at all.

It is most important to understand how thevideotape functions in the video recording process. As was mentioned inChapter 5,a recording head produces a magnetic field which stimulatesthe magnetically-sensitive material on the videotape in such a way as to record and store picture and sound information which can be played backlater.

Comparison with Film Recording

Film consists of various layers of chemicals onan acetate base. In contrast, videotape is a layeredconfiguration whose surface has a magnetic coating of needle-shaped iron-oxide or chromium-dioxide particles which lie in a length-wise direction on the tape (helical scan only). A binder material holds these particles in place and makesthem adhere to the polyester base. The magneticmaterial determines the tape's magnetic properties such as frequency response, sensitivity and SIGNAL-TO-NOISE RATIO.

Signal-to-noise ratio measures the amount ofpure picture or sound signal as compared to theamount of grain or "noise" (interference) in thepicture. The higher the ratio as rated in DECIBELS (db), the cleaner the picture. The surfaceof the tape (emulsion side),which is the side facingthe VTR heads, is dark gray and is highly polishedto minimize wear on the heads and to maximizetape-to-head contact. The back of the tape is usually flat black and coated with carbon which reduces static electricity caused by the friction ofthe tape against the tape guides. This type of tapeis often called CARBON-BACKED.

There are several kinds of tape on the market,The most common isthe IRON OXIDE type tape,in use for many years and now improved considerably. Newer type tapes such as CHROMIUM DIOXIDE and COBALT-DOPED type producegreater frequency response and have a longer lifethan the older iron oxide type. Eventually, magnetic tape itself will be superseded by a solid-staterandom access memory system that will take theform of a small magnetic card, cube or cylinder.

High-Energy or High-Density Tape

All 3/4-inch, Betamax, Beta-2 and other new 1/2-inch formats utilize only HIGH-DENSITY tape.This tape requires a higher erase and recordingcurrent than standard iron-oxide tape and shouldnot be used for recording on VTRs that are notdesigned for high-density tape. Certain 1/2-inchEIAJ color editors, specifically the Sony AV-8560and the Panasonic NV-3160, have a dual-functionswitch that allows them to usebothstandard 1/2-inch tape and high-density tape (Sony V-72).High-density tape should always be used whenpossible, especially in editing as the picture quality and image sharpness is considerably superior (about 3 db) to standard tape.

The ability of the tape store information isexpressed in density of particles or OERSTEDSOF COERCIVITY. Standard 1/2-inch EIAJ reel-toreel tape (Sony V-32 or V-30H) is rated at 300oersteds, whereas the Sony V-72 1/2-inch cobalt-doped high-density tape is rated at 530 oersteads, and Betamax tape is rated at 750 oersteds.

Videotape Characteristics

Unlike film, any piece of videotape will recordboth black-and-white and colorsignals. However,color isNOTa function of the videotape, ratherit depends on whether or not the camera, VTR orTV monitor is black-and-white or color.

Videotape determines picture quality. No matter how sophisticated the video hardware, theresulting picture quality is only as good as thevideotape used. Manufacturing videotape properly requires expensive equipment and extremelystrict quality control. Unfortunately, videotapetends to be expensive because the process of manufacturing is complex and critical and requirescostly petroleum as a major raw ingredient. Anhour of 3/4-inch videotape retails for $25-$35 with slightly lower costs for 30 and 20 minute tapes,

There are many brands of videotape on themarket, some very inexpensive, which are usuallyused tape from TV studios-2-inches wide that iscut up into 1/2-inch tapes. Often this tape clogs theVTR and leads to expensive breakdowns andvideo head replacement. Unless you test it first,you can't tell how bad the tape really is until afteryou have recorded some very important programson it. Then it begins to break down and looseparticles will clog the machine. Use of computer or instrumentation tapes also involves a definite risk to the VTR and program material. Most people who use these brand "X" videotapes regret it sooner or later,

The best rule to follow is to use only tape recommended by the VTR manufacturer. If this is impractical, Sony tape is the helical scan standardfor videotape by which all other brands are measured. Sony tape will work well on nearly anyhelical scan VTR. Other brands are MEMOREXand 3M. Even Sony manufactures bad batches of tape occasionally. If this happens, tape can be returned to the distributor and exchanged.

Extended-Play Tapes

Certain manufacturers offer EXTENDEDPLAY TAPES. Dupont has a 90-minute 3/4-inch standard size videocassette and a 30-minute KCS type (smaller size 3/4-inch) videocassette. Panasonichasa 90-minute''/2-inch EIAJ reel-to-reel tape and3M manufacturers the 30-minute extended playtape for use with the Panasonic and Hitachi1/2-inch EIAJ cartridge VTRs. The only way to gainthe additional recording and playback time is tomake the tape thinner—a factor which can increase the chances of the tape breaking, developing more dropouts, deteriorating faster and jamming the cartridge or cassette VTR.

CAUTION:Useof thinner tapes is not recommended for heavy use situations, such as mastering, still framing, editing or mass duplication of important programs intended forlargescale distribution.

How Videotape Works

Like film, videotape is the image storage medium. But unlike most film, videotape contains thecapacity to storebothpicture and sound. Bothfilm and videotape record individual pictures orframes of information. 16 mm motion picturefilm records 24 individual frames every secondwhile video records 30 frames a second.

These frames are visible on the film along withthe sprocket holes which control the rate at whichthe images are run through the camera or projector. The sound track is placed next to the pictureimages and synchronized to match them. Soundto-film sync often requires additional equipment

A nice feature of movie film is that you actuallycan see the individual pictures. With videotape,the frames are not visible to the eye, but they are present in a series of diagonal lines formed by the magnetic particles on the tape.

Videotape Dropouts

Videotape DROPOUTS occur when a piece of the tape's magnetic oxide or coating flakes off oris rough. This causes a "hole" or missing line ofinformation in the picture when viewed on themonitor during tape playback. Since dropouts area function of the tape and not the VTR, they arevisible only when the tape is played back.

These "holes" or missing lines of informationare created when the video heads fail to contactthe tape firmly and skip over it because of roughness, hills and valleys or actual missing flaked-offpieces of the oxide. When the tape particles flakeoff, the tape can never contain or store information at that point. Once a dropout occurs, it can'tbe corrected physically. Nearly all newer VTRs, especially the color models, feature electronicDROPOUT COMPENSATORS (DOC) or ONE-LINE DELAY circuits which electronically substitute or repeat the previous intact line of videoinformation, thus electronically "covering up"the dropout. The circuitry senses the dropoutwhile it occurs and replaces it with a good line ofinformation, thus eliminating the appearance ofthe dropout on the monitor.

Dropouts are bad enough in black-and-whitebut can become intolerable in color because thedropout is so much more apparent in color. Forthis reason, all color VTRs (except some earlymodel Sony AV-8600s) contain one-line delaysystems. Occasionally, dropouts will exceed theability of the one-line delay system to compensate, and some dropouts will sneak through.

One-Line Delay System Adjustment

The one-line-delay system may need adjustment when it fails to cover up dropouts adequately. On the Sony AV-8650 a marked control becomes accessible by removing the VTR from itscase. While watching the tape playback on themonitor, you can play the tape with the dropouts and adjust this control for maximum compensation.

Dropouts often occur at the beginning and theend of a reel of tape, and because of this, youshould never record important scenes on theseportions of the reel. Tape will accumulate dropouts with use, age and abuse. Sony videotape specifications indicate that up to 25 dro pouts-perminute can be expected throughout a reel of1/2-inchtape. If the dropouts really become constantand annoying the tape should be discarded orused for expendable programs. Loss of sync andpicture instability can occur when you have 2 or3 dropouts per second.

Videocassette Tape

The appeal of videotape recorders to homeusers and nontechnical persons always has beenlimited by the hassles of threading and handlingreels of videotape. Far greater use of the audiomedium immediately followed the introductionof audiocassettes and cartridges and the design ofself-threading self-contained audio systems. Thesame has been true with video systems. The videocassette system has made it possible for manymore people to deal confidently with videotapeand videotape recorders.

Although videocassette tapes have many positive features, they also have certain drawbacks.These features and problems are dealt with specifically inCHAPTER 11—All About Basic Videocassette Systems.In the meantime, we will proceed to examine how everything gets plugged together, and how you can make the right connections.

CARE OF VIDEOTAPE

• Do not smoke in or near or within several rooms of VTR equipment. Checkair flows

through building.

• Keep VTRs covered at all times when not in use to minimize dust accumulation.

• Keep VTRs as clean as possible.

-Use same size reels for supply and take up.

-Minimize hand contact with recording part of tape.

-Do not wrinkle or bend tape.

Do notexpose tape to dust, moisture, heat or extreme cold.

•Avoid high humidity.

•Always keep tape sealed in package when not in use.

•Never stack tapes on top of each other—store tapes vertically at room temperature.•Cut off any wrinkles and severely damaged tape ends.