:onte

BY FRANK LOVECE

A bi-weekly suraey of technical de'aeloprnents in the hardware and.software sid.es of the home aideoind.ustry.ttFou*-t"AD

vcR" is one ofthose marketing terms,, like "rackand pinion steering," that soundsgreat even though most people haveno idea what it means. It's also animprecise tefm, since it refers onlyto a VCR's video "heads" and not itsaudio "heads."

Audio and video heads are tinyelectromagnets inside VCRs.They're the physical componentsthrough which audio and video sig-nals come in contact with blanktape-they "pick up" and "laydown" pi,cture and sound informa-Jionl

Most VCRs each eome with a pairof video heads. Some high-end mod-els come with three, four-or evenfive. Each video head is split in twoby a gap where the electromagneticenergy that channels audio/videosignals is focused. The size of thegap afiects picture quality for play-back effects (freeze-frame, sJow-motion, scan) at the various tapespeeds. (VHS-format VCRs general-ly offer three speeds, or "modes";Beta VORs generally bffer two; and8mm VCRs may have either one ortwo.

Since the average consumer maynever ask or care about head-gap,widths, the onl;' thing you reallyhave to know about them is thatthey do vary-and that the width isoften a compromise. Ideally, eachtape-speed should have a pair of vid-eo heads with gaps suited precicelyto iL Instead, gap widths are usual-ly an all-purpose average size.

Immediately you can see one ofthe advantages of having four videoheads-with two pairs of:heads, andtwo different gap widths, each pairis closer to the ideal for each speddthan a sinele averase width could

be. This translates to more variedplayback effects in more mbdeswith less visual noise.

You can also begin to see that vid-eo heads are a lot more complexthan the familiar audio heads foundin audiocassette recorders. Theamount of information needed to re-produce a TV picture is immense-even engineers find it a small mir-aele that home VCRs exist. Video-tape machines themselves wouldn'texist were it not for the develop-ment of fundamental improvementover the way audio signals were tra-ditional recorded, namely, helical-scan recording.

It works this way: as in audio cas-sette recorders, a VCR's audioheads are "fixed" or stationary; vid-eotape runs by it in a straightfor-ward, "linear" fashion.

Video heads, on the other hand,rotate on a cylindrical "head drum".at an extremely high rate of 30 revo-lutions per second. Together, thetwo video heads in use at any onetime lay signals on videotape 60times a second in slanted tracksacross the width.of the tape. Andthat's basically all that helical-scanreeording is. Another way of refer-ring to it is azimuth recording, aterm taken from its method of re-

(Cantinued on'nent page)

42'-,/d-t*r:di.

FAST FORWARD(Continued from preceding page).

cording adjacent tracks at differentangles for technical reasons..

Basic VCRs have not only a pairof helical-scan video heads, but alsoa fixed audio head which puts a sim-ple linear audio track on the edge ofthe tape. (This is also called the"longitudinal" or "edge" track.)The audio head generally is also re-sponsible for laying the "controltrack," which helps "guide" videosignals. All you really have to knowis that to correct control-track prob-Iems, use the VCR's tracking con-trol until you get the VCR serviced,

On VCRs with two video heads,the heads are located across fronieach other in the head drum, 180 de-grees apart. On VCRs with four vid-eo heads, the heads may be at com-pass points (90 degrees apart) or inpairs at opposite sides of the drum.A few units, primarily Hitachi-made, have five video heads in acompass-point configuration withan extra head just off one of thepoints. The Betamovie camcorderuses a single "dual-azimuth" videohead that can record tracks at bothnecessary angles.

Want more? Aside from up to fivevideo heads and an audio/control-track head, there's also a fixed au-dio/video erase head. As the nameimplies, this initial head in the tape ,

path automatically erases audio4nd ,,

video signals when you want to re- ;

cord over existing material. It's afixed head except in the case of in-dustrial and some Smm VCRs" j\whieh cases you have moving-so- -called "flying"-erase heads.

Finally, there's Beta and VHS Hi-Fi. As you're probably aware, BetaHi-Fi and VHS Hi-Fi VCRs recordsimple audio signals using the samemethod as for the complex videosignals, high-speed rotary heads. Inaddition to the standard audio edge-traek, hi.fi audio signals are actual-ly "multiplexed" in slanted tracksaeross the width of the tape, along-side the video tracks.

On Beta Hi-Fi VCRs, the existingvideo heads do double duty by alsorecording and playing back hi-fi au-dio. VHS Hi-Fi VCRs adoptan extrapair of audio heads mounted withinthe head drum.

Add them all up, and you can ac-tually have a VCR with nine heads:five video, two hi-fi audio, one linearaudio and one erase head. The term"four-head VCR" still won't goaway, but for those in the know,"four-video-head VCR" is a moreuseful phrase.