VCR Basics - Video Head Configurations

[Music] so before i get started showing all the different types of head configurations just a quick background these heads read the video tracks on a videotape as shown in the orange and blue on the screen the control track at the bottom is unrelated audio track at the top for linear audios unrelated and we are concerned with the video heads themselves there's two properties to the video heads there's the head width and the head gap the head gap on each opposing head is at an opposing angle or azimuth in the case of vhs plus six degrees minus six degrees um i'm not going to get into the details of this but it's basically to eliminate crosstalk between the two adjacent tracks but what we're concerned with is head width in this case and just as a quick background this diagram here the angle of the video tracks versus the tape itself is called the helix angle helix angle i'm showing here is completely wrong it's just for demonstration purposes it looks closer to this but the problem with this is i can't show a whole video track so this helix angle is not going to be shown helix angle is also affected by the tape speed itself so as you slow down or speed up the tape with different play and record speeds or using special effects fast forward rewind scan or even pause you change the angle so i'm not going to get into details with that yet but yeah just keep that in mind first up the most basic head configuration two video heads take a look at the head drum here you'll see there's one head and the other head here head a head b and you can tell it's two heads because you have three screws three screw holes or adjustment holes above each head don't mess with the adjustments that just just don't you'll never need to in your life but yeah this is a very basic configuration the minimum required to play back video and what the original vhs spec was built around downsides this doesn't take into account special effects fast forward or wind scan pause it also doesn't take into account different plane record speeds so for example if you have multiple record speeds you now need a head width that can support those multiple record speeds you can't have a head width too wide you know configured more for sp because then it's going to have trouble playing and recording the slower speeds that have a narrower track width need a narrower head so on most two head models that support multiple video record speeds you're going to have a narrower head width than would be ideal for say playing back and recording sp what that means this will play and record slp or ep just fine and it'll work with sp but the quality of the playback on sp won't be as good it won't be optimized for sp second problem special effects these heads like i said the angle when these heads are hitting the tape changes depending on the speed so when you have a narrow tape head and you're playing back sp and then you hit pause suddenly the angle changes now you have this narrow head that's not able to capture as much information as a fully wide head so you're already at disadvantage because your tape speed has changed now you're at a double disadvantage because your head is narrower so you're going to get a lot of noise on the picture same thing for with fast forward and rewind scan you're going to get a lot of noise on the picture now with slp or ep you're going to get a lot less noise because the head width is more tuned to the recording speed or the track width but it's still not going to be great you're still going to be getting flickering and jittering and that's because you are paused and you are constantly flickering between two different heads that play back two different fields of video and one of them is going to be hitting the tape or the track a little bit better than the other so it's not going to be great it'll be better but in both scenarios special effects won't be fantastic on this how do you support optimal quality for two playback speeds you add two more heads so that's what they did this is a model that has four video heads as you can see they're still at opposing eight angles 180 degrees from each other so there's two and there's two more so the way this vcr works is depending on what speed you're playing back it will use different heads to play back that video or different heads to record if you're recording the sp optimized heads will be wider and this varies from manufacture to manufacture what the actual width is same thing with the ep heads they can range from i think the older machines were like 20 to 31 microns in width and sp ranged from 38 all the way up to like 70 or 90 for for maybe one of the sp heads different heads sometimes like one would be a different width than the other for trying to optimize with special effects but the long and short of it is the sp heads are wider the ep heads are narrower this means that you get your best quality you can playing back sp while still being able to play back ep with the narrower heads this did improve special effects on sp as well because again your head is a proper width but only as good as the special effects were on say like a two head with ep they still weren't great your screen wasn't completely full of noise but it wasn't a hundred percent but this is a good step to being able to properly support two video speeds but what about special effects what if you want to get better special effects well they added one head to a two head configuration to add this special trick or special effects playback head if you take a look here you have one head on one side you have two on the other and if you notice these two heads are right in the same spot they're basically built into each other and this is what's known as a dual azimuth configuration meaning that on this side these two heads read the opposite azimuth to each other so one way to describe it is this is head a this is head b and this is set a prime a prime being 180 degrees away from it but recording and playing the same azimuth what this means is when you're say paused a and a prime are being used to display the video information so a will read the a will read one field and then a prime will read the same field on the video tape so you're not going to be jittering back and forth these are both going to work together to show you one field of video so you're not going to get that interlacing jitter and usually this trick head is a little bit wider to be able to get more information so you're going to get excellent pause excellent fast forward rewind scan on both speeds but this doesn't give you any benefit for playback you're still only playing back with two heads a and b so what if i want optimized playback and recording quality for both speeds and i want good special effects well combine the two give yourself five heads this is a five video head head drum and you can see you'll have your sp heads and your ep heads or slp heads and then your fifth head for trick playback now this one is in a 90 degree configuration whereas that other one i showed i think it was like 15 or 20 degrees off uh different manufacturers had them at different angles it really didn't matter for a forehead model for five heads when you get into the trick playback i believe these had to be 90 degrees out that's why they're in this this pattern but this gave you the best of both worlds this gave you good special effects and this also gave you optimized quality on both speeds but it's kind of expensive having five separate or i guess four separate heads one of which is a combination of two this is pretty expensive to manufacture there's got to be a cheaper way to do it what if i combined a three head and a forehead vcr together in a different way so instead of having five heads i have four heads but i have two in a dual azimuth configuration and two more in a dual azimuth configuration then side by side i set them up for the widths of sp and ep what this means is that i have four playback and record heads so i get optimized playback and record on both speeds but i also get trick heads and i get two trick heads so with a bit of logic inside the vcr it can go and pick and choose which head gives it the least amount of noise has the best signal and you end up with a forehead dual azimuth or 4da head these are the most common forehead vcr you will see out there once we got into the 90s pretty much all other configurations other than two head and forehead dual azimuth were dead so a non-dual azimuth forehead very uncommon three head five head also very uncommon this was sort of the final design that gave the best optimization it was the most cost effective it gave the best of both worlds and so yeah almost all forehead vcrs out there especially nowadays are you that you'll find are gonna be forehead dual azimuth like this now i just want to mention the hi-fi audio heads they exist on the same video head drum as the video heads and all the configurations that i've already shown were available in hifi my little graphics all showed the hi-fi head location but honestly they're pretty rare um the most common hifi models i've seen were either some higher end five head models or your forehead dual azimuth two head hifi existed very uncommon three head hifi existed very uncommon forehead non-dual azimuth also pretty uncommon but they did exist but here's an example of a forehead dual azimuth and it's got these little hi-fi heads on the side here the way hi-fi worked is because it was at a lower frequency it would essentially record deeper into the magnetic tape than the higher frequency video information so they used something called record under that would record the audio first then the video over top and the video wouldn't completely overwrite the audio that was already underneath that's a very very uh simplified explanation of it but the advantage is you get the same or similar bandwidth to video for audio so the audio is excellent and one other thing i want to mention sometimes a forehead plus high five ecr will be called six head it's not as common in north america but i see a lot of european models that would say six head and a lot of cheap manufacturers would say six head and what they meant was four video plus the two hi-fi i completely disagree with that as far as i'm concerned the head count should only be for video uh six head models do exist but they are not this one this is a forehead plus hi-fi model this is a six-head vcr a proper six-head vcr you have your video heads your dual azimuth four video heads you have your hi-fi and you have two additional heads here so what are these for well it's all down to head width again so if you look at the vhs spec the width of a track for ep is 19 micron so later in the 90s when technology and tape formulations and everything got better there was this new trend of 19 micron heads well what does that mean it means that your ep heads are very narrow narrower than the typical 25 to 30 micron the advantage is you get less noise because you can narrow you can get right narrow on the video track the downside is stuff that was recorded with the old wider ep heads wouldn't play as well on the newer 19 micron heads so for a short while in the mid 90s manufacturers sold six head vcrs that had two sets of ep heads your traditional ep heads and your 19 micron heads eventually they just went back to the 4da configuration that you had sp and then you had your 19 micron ep heads but six head vcrs for six video heads did exist and uh yeah kind of a gimmick but uh there you go one more thing i'd like to briefly mention is what's called a flying erase head and that is basically when an erase head is added to the video head drum itself you can see here there is the forehead dual azimuth there's your hi-fi and there's this additional head right here and that's what's called a flying erase head flying i guess because it's flying along like this with the video heads so why is that useful well it has to do with how a vcr records onto a tape and the position of all these pieces so the first piece that touches the tape as it passes through a little m configuration here is this erase head it's called the fully race head erases the entire width of the tape so the tape is now empty tape is traveling through this empty tape gets recorded on with the spinning head drum so the video information or hi-fi audio it will and hi-fi audio information if it's available is recorded helically so at an angle then it goes past this head here this is the linear audio head control track head and audio erase head so if you take a look there's a little head on the top of the silver thing that's your audio a little head on the bottom that's your control track uh head and if i can kind of get it shown here see that little shiny piece at the top of that black head that is your audio erase head why is there an audio erase head well the video head has just recorded across basically the entire tape it's just swiped right across it right so you don't have a nice fresh erased tape you have a bunch of crap on it and if you record over stuff that's already recorded you're not going to get the best quality you really want to properly erase the tape before applying any information it'll still work it just won't work as well and when it comes to analog linear audio you kind of want the best this erases that little track before you record onto it for the control track pulse it doesn't really matter it just vcr just has to be able to read it it's not like a audio quality thing so it doesn't really need to be erased again it can just go right over top of the information but again why is a flying eraser important well if i put a tape in here and i hit record there is tape that's goes from here all the way around and when you hit record it will start recording at an angle along this tape so there's a section of tape here that isn't erased that you're recording on top of now i don't know the technical reason why but this really seems to have a negative effect on the color when you're recording the color information over the old one it bleeds through and you get that sort of rainbow effect and that rainbow effect will peel down as this head drum records more and more onto it again at an angle that's why it's peeling down so what a flying erase head does it erases the information on the tape right before it's recorded and this is very useful for editing if you want to insert some video you don't want to have this weird angled mess of extra chroma information causing a bunch of color on the screen so a flying erase head really helps with being able to just hit record and it inserts the video information right there and while i'm at it i've been meaning to do this i haven't had this thing open in a while there be gone with you into the pile [Music] we

Channel: probnot's tech

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Length: 17min 56sec (1076 seconds)

Published: Tue Apr 27 2021