5/28/2018

Digitizing Analog VHS tapes - to AVI or to DVD


Among "digitizers".. people who want to transfer or convert their VHS tapes to PC files or DVD media there are two camps.

First are the professionals who know every detail about quality and quantity and do it as a business.

Second are the casual users of VHS tapes, who have not used them in years or infrequently and now find they want to perform this quickly and as a means to finally get rid of the tapes.

Among the first category are websites and forums that are mostly going quiet these days, occasionally helping one another to care for the equipment they are using to make these conversions, and answering few questions from "newbies" to the profession or hobbyist who happen to just be starting.

First its important to understand the last VCR was made in 2016 and the tapes are also no longer being made. Every year the tapes get older and degrade and these forgotten memories move closer to oblivion.

Of the remaining VCRs most are not well maintained or cared for and decay from misuse.. or become damaged from being plugged into fluxuating power lines and lightening strikes. If they don't end up being recycled or tossed in the dump.. they are given away.. and a very few end up on eBay or Amazon or Craigslist as "used".

Among the second category users generally start out with a combo VHS to DVD or some USB dongle to perform the "captures" and are sorely disappointed with their results.. they turn to the web and find the "prosumer or professional forums" and discover a new world of choice and information that tends to overwhelm.

There is also almost a "stages of grief" that sets in from the gradual understanding that what they were attempting has many levels of quality and generally the professionals tell them they've been doing everything the wrong way.. so they get their standards wound up and upgraded to "pure" and "archival quality".. seeking legenday and near mythical "unobtainium" in the role of VCRs with digitial noise filters and line and frame "Time Base Correctors"..

Eventually if they don't quit.. or run out of money and hope.. they discover the easier "MPEG2" path.. a lower bit rate and quality that for some is "good enough" and subscribes to a lower spec than "absolute perfection".

In or around 2003 to 2008 there was a fleeting moment in time when $500 to $1500 DVD recorders were "Staged" to replace the VCR as a means of copying broadcast television to DVD discs.

These could also be used to "capture" the VHS tapes being played back to DVD discs.

Unfortunately with success also comes the realization that the DVD could not hold as much per disc.. so people sought to edit out "commercials" or beginning and end credits for seasons of shows. Doing this by DVD recorder alone with no intermediary was "impossibly difficult".. enter the combo.. Hard Disk (HDD) and (DVD) recorder.. which could "Capture" even the longest tapes to its internal hard drive and let the user selectively edit and rearrange material and burn "title lists" to a single disc or break up the list and burn groupings of "title lists" to sequences of DVDs one after the other.

Great in theory and practice with a little experience.

But then all of the major makers of DVD recorders and HDD/DVD recorders disappeared one day.. and the remaining recorders aged and the DVD burners begain to wear out.

So people then looked towards settling for capturing DVD quality to PC files.. but the capture equipment usually (with a few exceptions) would not allow copying the large MPEG2 files used to create DVD discs to a PC.

Which then brings us to the Home Theater PC.. a complicated mix of presentation and workstation editing capability. Generally these are not designed with editing and archiving in mind and support is near non-existent. The standards unlike DVD or MPEG2 for DVD, rove all over the file type landscape and confuse to no end.. mastering or "authoring" a DVD from files captured to a HTPC is a soul crushing exercise.

A single maker of an HDD/DVD recorder lasted until 2017 "magnavox" and then mysteriously did not deliver a set of three new recorders in the last half of that year.. stranding many archivist with no way to finish their conversions.. or soldier on.

5/27/2018

fit-PC2i Atom 510 - Centos 6.9 i386

The fit-PC2i was a low power dedicated server module from Israel with many customizable options, mostly intended for do it yourself custom firewalls running a version of 32 bit linux or Windows 7

It comes from around the years 2008-2010

Many linux distros no longer support something so low power, or exotic.

However Centos 6.9 i386 will install on this device.

The IODD portable combo USB - CD/DVD rom drive emulator and simultaneous USB hard drive is a great way to boot quickly and switch between many ISO images. A special directory on the IODD is labeled ( _iso ) and in this directory .ISO images are placed.. a combo jogwheel and selection button on the side of the drive case allows scrolling between images inside this directory and "mounting them".. the selection is saved to a Fujitsu based microcontroller in the drive case and immediately this is presented as a USB attached CD/DVD rom drive with the selected image mounted as if it were an Optical disc.. no burning, no "actual" optical media needed.

Upon reboot the last selected disc image is automatically presented as a bootable device option. the drive case also simultaneously appears as a seperate USB hard drive, which is very convenient for offloading or onboarding files to and from an operating system that can mount the virtual attached optical drive and virtually attached usb hard drive.

The fit-PC2i has a half height microSD slot for flash media or four USB ports, two Type A and two microUSB ports.. and a drive slot for a SATA drive.

Unfortunately the support site recommended Ubuntu Desktop 8.04 as a boot option.. but this had a "Bug" in that if a SATA drive were installed, it would not be seen by the boot installer kernel.. frustrating to say the least.. the Centos 6.9 kernel correctly "sees" the SATA drive, and using advanced options during partitioning.. even allows checking off drives to use, or unchecking off drives to not use when installing the linux operating system on the device hard drive.

This is a metal case, passively cooled device.. so it generally gets "hot" and a USB powered external fan like the "AC Infinity" line up with inline speed control and rubber shock absorbers makes a very low cost and effective cooling solution.. and is very quiet.

The dual LAN ports make this Ice Cream sandwich sized server a fairly flexible platform.

Toshiba xs54, xs55 - Net Dub (copy) to PC

A random websearch turned up a 2008 blog article in Japanese regarding the xs37 (a model sold only in Japan) with a "Navi from Net" feature called Net Dub.

Net Dubbing is a term for Network Copying or "Duplicating.. hence Doubling.. or Dubbing" a rcording to another xs37 or other recorder.

As a hand held remote "workstation" for mastering and creating DVD recordings..  shuttling recordings before editing from one workstation to the other was taken into account as a desirable feature. The recordings are "not" transcoded but are at the same resolution as they were in when originally recorded.

PCs don't normally participate in Net Dubbing.. however they can with a simple protocol daemon that listens for a Netbios broadcast requesting XS recorders identify themselves with their Anonymous FTP server paths.

A simple systray windows application was created and released as Freeware. I modified the text labels for English and the result was a Virtual RD-XS recorder service for the PC.

Starting this allows you to set a download path for recordings "pushed" to the PC from the Net Dub interface on the XS recorder. The title or name for a recording on the XS recorder is used as its destination filename on the PC. An extra txt file is created with any metadata associated with the recording.

4/28/2018

Toshiba HDD/DVD Recorders

After some research and purchases on eBay, I now have one of all the major RD-XS hard disk equipped DVD recorders.

The flirtation with replacing VHS tape based recoders with DVD optical disc based recorders had problems. The optical media usually consisted of a choice between cheap write once media or more expensive read/write media. As with tape based recordings commericals and other material was recorded at the same time, however where tapes could be recorded in 2 to 8 hours per cassette, the degree of quality that suffered when recording non-standard low bit rates on optical disc was much worse. So it became even [more] desirable to perform some type of editing before burning the recording to disc.

Enter the hard disk drive familar from personal computers. Some DVD recorders included an 80 GB to 500 GB hard disk drive, which was nominally used as the default for capturing the off air broadcast. Various electronic program guides or timer based recordings could be used to automatically select programs or series of programs from a season of one or more shows and store them on the hard drive. From the hard drive one could then watch the programs and recycle the  hard disk space without burning to optical disc or [edit] out commericals and beginning and ending titles to save space and use the saved space for more episodes or to keep the bit rate higher for a better quality recording to disc.

This was the TiVO concept evolved from a DVD recorder into something like a Personal Video recorder without a normal monthly or yearly subscription to the program guide made popular by the TiVO business model.

At the turn of the Video era when NTSC analog signals were stopped and replaced by ATSC over the air, the requirement for a new ATSC tuner drove the price of the combined HDD/DVD recorder so high that many companies exited the market.

Until that time however there were a few companies that offered increasingly better and better off air recordings to hard disk drive that also digitized or encoded the analog content into MPEG file format.

Among these were the Toshiba branded "RD" for "RD Life" series of "XS" HDD/DVD recorders.

warning: These recorders are very dependent on their Remote Controls for buttons, the front of the consoles do Not have a complete set of control buttons. These recorders are not usable without their original OEM remotes, programmable and universal remotes are inadequate as replacements due to the complex documentation that refers to the OEM remotes.. it is not possible for a user to perform the complex mental translations necessary to use a universal or programmable remote with the OEM documentation in any reasonable fashion. Do not try it. Further each model has a Unique OEM remote model.. they are not usually compatible between generations or step-up models. If matching a second hand OEM remote to a model without its original OEM remote be very careful to note the OEM remote model.. they absolutely must match.

Simply.. do not buy a Toshiba RD-XS without its "original" OEM remote.. and make sure it is included as part of the terms of sale.. or return it.. its not worth the trouble.

It is [Very] common to find the remote [Not] included as a term of sale, or substituted with a generic.. or the terms will say "as..is" and "no returns accepted".. the remotes sell for quite a bit more seperately from the recorders by themselves and are often prized [above] the actual recorders themselves because the recorders are useless without them.

Basically Toshiba made many many different models for the Japan and outside the US and North American markets, only a few were brought to the Canadian and US markets and not necessarily the same models.

They arrived in three waves:

XS-32, XS-52
XS-34, XS-54
XS-35, XS-55

The second digit representing the "generation" of the recorder.

The first digit repesenting the "feature" level of the recorder.. also called a "Step-Up" level.

Within each generation the same DVD burner was used, all used an ATAPI packet based command language to burn discs.

The 50's included "progressive upscaling HDMI output" for playback only.

The XS-32 and XS-52 were known to have a problem with their handling of the IRE set-up or "Black-Level" definition in the US markets resulting in DVD discs burning on those recorders looking correct when played back only on those recorders but appearing washed out or black level elevated to "grey level" and "white-level" blown-out resulting in a loss of contrast or dynamic range.

While this could be corrected in software, the loss of dynamic range could not without preconditioning on the input signal to the recorder.. a device to effect this change was never manufacturered.. and a software fix accepting the inevitable loss of dynamic range in exchange for a normal playback of discs on all recorders was never made available. Only DVD burner drive firmware updates were ever made available to consumers via their website or later only by firmware discs only available from the manufacturer through the mail.. after the firmware was removed from the website.

Several "revisions" of the motherboard and motherboard firmware for the XS-32 and XS-52 were observed in the "wild" by consumers, but no means of deploying "updated" motherboard firmware was ever found.. the newer firmware judging by the firmware versions between motherboard "revisions" was "as-is" from the factory and considered immutable.

These were considered quite advanced "workstations" approaching the flexibility one could have mastering or authoring disc creation on a personal computer with specialized software and world wide had a great reputation.

While external proc-amps could be used in the US to attempt to correct the input capture problem with Black Levels.. quite a bit of tweaking was necessary since it also involved stretching the video signal over the dynamic range while avoiding clipping of blacks and whites and compensating the loss of chroma gain and skewing in the tint.. at best it was a complicated bargain.

The XS-34 and XS-54 would see firmware updates "specifically" to compensate for the Black Level problems in the previous generation in the US and Canada and while having a lackluster physical case appearance are considered the most desirable by collectors. They had very durable Panasonic style DVD burners with long life when serviced to remove dirt and grime on a regular basis and were on the whole quite economical. In some ways they were considered the apex of the product line. However the UK version XS-34SB and the European XS-34SG (were Not) capable of NTSC capture.

This was quite different from Panasonic and Pioneer recorders which could decode and capture NTSC signals in their UK/European world models. The XS-34 UK and European models often appear somewhat similar to the XS-34 US model but are (Not) desirable in the US or Canadian markets even if the tuner is of no issue.

In particular the UK model does not appear to have SCART connectors on the back and can be mistaken for a US model.. since the XS-34 (US model) can be quiet rare and hard to find it is a common mistake to acquire an XS-34SB or even an XS-34SG model (that does have SCART connectors on the back) thinking it "might" record NTSC signals.. it will not.. and further it cannot output an NTSC playback signal either.

The XS-35 and XS-55 were the last of the Toshiba HDD/DVD recorders imported into the United States and the XS-55 was not imported into the Canadian market. While better in appearance they were still somewhat lackluster. They did contain many features that would never appear in any other HDD/DVD recorder. The XS-55 would continue to support "Net Dubbing" even between it and the previous version in which networked on a LAN they could copy recordings between the machines without first burning to disc.

2/08/2018

Retro-fitting DVRs with a usb port

DVRs began as a way of digitizing analog video signals from aerial broadcasts, they evolved to digitize VHS signals from tapes and personal camcorders to optical disc media. Because commerical movies were released on the same optical and aerial mediums, right owners weighed in and impressed upon the designs, varying methods of protecting copyright.

Consumer video products have long since moved on from Standard Definition (SD) video products, but the older analog signals captured on personal tape based recorder products remains. Regardless of the rights management issues which have withered away and made digitiziation more difficult.. the lack of a method to even extract the MPEG2 stream from a video to optical DVD burn has consigned many DVRs to landfills or abandonment.

Many brands of video recorder have at one time or another used commodity optical disc "DVD-R" burners, which almost universally rely upon the ATA Programming Interface (ATAPI) to conduct a recording session over an IDE (PATA) or SATA bus. These are not new designs, and are well documented. The signaling cables are standardized.. and although there was flirtation with removing the microcontroller unit managing the IDE bus from the drive motherboard and placing it closer to the DVR main motherboard.. integrating it or placing it on a daughter card.. in later years.. often the signal paths remained accessible down closer to the mainboard.

That means with exceptions.. many designs had a common internal IDE signal bus, with a max speed of 25 MHz for UltraDMA100 and often ran much slower.

In fact the CD and DVD xSpeed standards would often run only at the speed of that negotiated for a particular DVD-R burner drive and for the most part remains x8 or lower for stability and due to the speeds available to cost constrained microprocessor equipment up to about 2006.. although the equipment might run into the $100s or $1000s of dollars.. the tech was simply much slower than today.

Enter the 8051 and CY8C5 generation of dedicated real-time microprocessors driven by the phone industry and other evolutionary pressures. They are much cheaper and faster than earlier 2006 cost constrained microprocessors in the DVRs. Its possible a modern mcu could be used to emulate a device on the existing IDE bus by "learning" the signal conversation and then extract the MPEG2 stream destined for the optical media as a stream of ATA packet commands transfering data, then directing that over a USB 2.0 bus to an external computer, iSCSI device, USB drive or a USB DVD-R burner of a modern design from a third party.

The small size and near complete SoC implementation on prototype boards from Cypress Semiconductor for $10 in single quantities makes it almost an excercise in software only.. with a few custom cabling requirements.. and choices over wireless or sometype of re-housed external port exposure through a faceplate.

Re-implmenting a near 30 year old IDE bus in a real time mcu using C code is no small task, but it doesn't seem insurmountable given that the bus has been thoroughly documented.. and the ATA PI interface is on the whole based on SCSI and a relatively small command set of about 40 words.

The benefits would be the continued usefulness of these aging devices for their original purpose and some possible retention of our media history.


1/25/2018

Y/C Combs, DNR and Twin Perfect

Television video signal is a combination of Luminance (Y) and Chroma (C) information into one signal. A Composite (or combined) version of these two signals on a single set of wires is called a video signal, it includes (no) audio or sound information.

Normally the seperation between the Y and C components of the video signal are distinct enough to recreate the video without error.. however the signal degrades over long wires as the Chroma information "smears" into the Luminance information effecting picture quality.

To preserve the Y and C components over long wires or poor quality wiring cables, it is better to keep the two seperate on two distinct signal pair wire sets. The S-Video standard was created to do this, and includes four total wires that are two sets of wire pairs. One pair carries Y signal, One pair carries C signal.

S-Video is a "wiring standard" and really has nothing to do with the "S" in S-VHS.

The "S" in S-VHS stood for "Super" and indicated more horizontal dot resolution or perceived Television Vertical Line (counts) also known as "TVL" .

Strictly speaking.. a Black & White picture of only Luminance information could be S-VHS and would have zero benefit over an S-Video cable.. they are entirely two different things.

S-VHS is about horizontal (across the scanline) dot resolution

S-Video is about (preserving) accurate Color information that might be lost and might destroy perceived horizontal dot resolution in the process of carrying the signals a short distance from the VHS player to the Television.

People often confuse or conflate the actual meaning of the two by saying one may effect the other.. in the final result.. the picture..  which is true.. but for different physical reasons that only (sound) like they are related.. in reality they are unrelated.

A Comb filter is used to "extract" the Y from the C information from a "Composite" video signal.

The video signal is (stored) on the Tape in a "Composite" signal format.

All S-Video VHS players have a Comb filter.


When the Tape is played back the Composite signal extracted from the Tape can be handled in one of two ways.

The Composite signal can be placed on a single wire pair and output to Television over a Composite connector, or the  Composite signal can be [broken down using a Comb filter] into a seperate Y and C signal and put individually on seperate wire pairs and output over an S-Video connector.

The Composite connector will provide a better signal to a Television than an RF connection. The Television will have less signal losses and produce a better picture.

The S-Video connector will provide a similar, but even better picture because there will be less Chroma crosstalk with the Luminance signals over the length of the connector from the VHS player to the Television.

Comb filters also offer the "opportunity" to improve the signal quality with filters and amplifiers tuned and customized to work on Luminance (Y) and Chroma (C) signals seperately which exist at different frequencies and are vulnerable to degredation in different ways. Analog and Digital "noise reduction" can be used to "process" the video signal recovered from the tape before it is output to the Television.. and this is called a [ processing amplifier ] task performed by a [proc-amp] for short.

Digital Noise Reduction (DNR) is both cheaper and considered more precise than analog noise reduction which can have non-linear characteristics (which are difficult to describe and teach how to use). Non-linear noise reduction is harder to repair or reproduce in similar or duplicate circuits.

Not all VHS players have NR or DNR circuits, as its considered a more expensive and premium feature.

Another way to improve VHS playback is to tune the tracking and control circuits based on the type of tape inserted into the system.

Mitsubishi pioneered a technique called "Perfect Tape" or "Twin Perfect".

Originally intended for "preparing" the VHS recorder function, it "samples" any tape inserted into the VHS recorder/player which does not have its write-protect tab broken off.. in anticipation that it may be used for making a new recording. By doing this it can configure or optimize various circuits in the VHS player to make the best use of the Tape provided and make the strongest recording possible. On playback it similarly is optimized to extract the best signal possible.

The on screen display for a Mitsubishi VHS player with this feature can be used to manually engage or disengage this feature on demand regardless of the state of the write-protect tab.

Mitsubishi VHS players also have a direct drive method of fast forward or fast rewind called "Turbo Drive" which was used to reduce the time a consumer was required to wait for a Tape to be wound or rewound for return to a rental store.









VHS drum heads, why so many

A VHS player was originally a rotating cylindrical drum spinning on an axis at a canted angle to a video tape pulled through a tape path. It had a seperate erase head before the drum and seperate audio head and speed signal control head after the drum.

The erase head simply "cleaned" the tape of any magnetic patterns before the tape was used by the drum heads to lay down new video information in angled or tilted tracks across the width of the tape. Each track represented one scanline across the width of the Television picture.

After the scanlines were recorded to the tape, the audio head would "skim" a small width at the edge of each scan line for its use to store sound information across the Left side of each scanline, and the Control track "skimmed" a small width at the opposite edge for its use to store tracking information across the Right edge of each scanline.

On tape this meant the very Top edge of the tape had audio information, and the very Bottom edge had control tracking information.

This didn't effect the picture much because normally those edges on the Left and Right of the Television image are hidden away under a varying sized bezeled picture frame around the central viewable image on the Television.

The audio track was mono (not stereo) in the first VHS standard. Dual tracks and HiFi were two different standards that would come much later. And by most relatable audio standards quite low in frequency bandwidth.

The control track was a timing signal which when played back acted as a feedback signal to the tape path drive motors to servo-regulate the speed of the tape as it moved through the system, so that scanlines and signal arrived at the playback Television at the correct rate in order to regenerate the video signal. If the signal was too slow, drive electronics sped the tape up, if too fast, drive electronics slowed it down.

Frame rate tracking, indexing or accuracy were never part of this Control Track mechanism.. certain specific manufacturers replaced this track with their own variation to encode extra information and provide either their own version of a frame or location tracking system.. or re-implemented the Society of Motion Picture and Television Engineers (SMPTE) frame accurate time code on the control track.. but this was rare and non-VHS standard.

Basically the VHS "standard" was feature-less and made to be cheap and easy to implement across many manufacturers and vendors. Broadcast quality producer level features were reserved for much more expensive and purpose built equipment.. or, non-VHS (non-Home) video equipment.

DV (for Digital Video) would later re-think and cross pollinate ideas from Broadcast features and Home video features to create a new "incompatible" video standard that would be low cost enough to be accessible to the Home video market.. mostly by way of the "Camcorder".. but it was not VHS... even though it did borrow some of its ideas to achieve its goals.

The confusion often led consumers to assume that DV was an upgrade or improved version of VHS, when actually it offered video with a different set of goals and compromises. In some ways better, others worse and definitely not media compatible.

Originally there were two video heads on the spinning drum. The M shaped tape path wrapping the tape around the drum allowed one head to complete one scanline copy to the tape angled from top to bottom along the length of its travel path. the next head would begin its traversal as the last head left the tape path and rotated out of contact around the backside of the drum.

So the minimum number of VHS player video heads was "two".

VHS had a specific tape speed, meaning the size of the video heads were fixed to optimize the size of the magnetic track based on this speed. The inital speed was called "SP"

When longer length video recordings were made possible by changing the tape "speed" the size of the video heads had to be changed to make the width of the magnetic tracks smaller.. so (two) additional heads were added for "LP" (Long Play).

And then additional heads might be required for "EP" (Extended Play).

The LP tape speed dropped out of favor and choice became SP or EP, even if SLP was advertised.. instead of changing tape speed.. the length of the tape was increased per cassette for SLP.. so tape speed was the same for SLP as EP... so in the end only two sets of head sizes were normally included developing into the (4-Head VCR as a consumer staple).

A "Flying" Erase head was also added to the drum so that the point at which an "Editing" Cut or Insert could be made closer to the actual point at which a video was stopped or "frozen" when playing and then engaging recording from a second VCR. This was a "Prosumer" feature rarely used by most people.. but made "Linear" editing near real time during playback on a VCR used for both playback and recording from other decks possible.

Previously the former Erase head was not on the drum and offset far enough that at the point where a frozen frame to new recorded video might overlap, or include "magnetic" bleed through of signal from a previous recording or random noise on the tape with a pattern.. leading to chroma aberations at the insert point. By moving the erase head closer to the actual recording head this problem could be minimized.

So that added a (5th) possible head to the VCR (not counting the original Erase and Audio and Control heads that were "not" on the drum)

Finally "offical" stereo was added to VHS, by [deep] recording an opposite angled, slanted set of audio tracks at a different frequency and magnetic strength to the video tracks. This minimized crosstalk between the signals and a bandpass filter could be used to further reduce the perceived "noise" in the video signal from the audio signal in the central portion of the tape normally used only for video signal.

Although this made stereo possible, at near CD quality.. it also introduced a perceived "buzzing" or possible interference when electrically switching from one head to the opposing audio head on the drum. Further bandpass filters were used to attempt to reduce the "noise".. but circuitry degradation over time meant the buzzing could increase over the years with older equipment. A technique some people used was to switch off the stereo track and fall back on the (mono only) track recorded for backwards compatibility (unless specifically used for different content like alternative languages, or narration it was a duplicate of the stero track) at the edge of the tape.. which would not have any switching-buzz noise.

The "mono audio track" is also sometimes called the "Linear audio track".. chosing between them is a good thing, [mixing] them is usually a bad thing (if they are backwards compatibility duplicates of the same sound track)  primarily because the two are physically located at different points along the tape path..any imperfection (which is very common) will introduce a slight difference or signal delay.. that manifests itself as a (tunnel) echo effect in the audio when both tracks are being played in [mixed mode].. over time on older equipment or older tapes this effect increases.

[Mixing] the stereo and mono tracks did have a purpose however, if they contained different content.. for example, an orchestral music content recorded on the stereo tracks, and a speaker, dialogue or narration content recorded on the linear mono track. In this way it was use as a simple audio "mixer" setup, and allowed for post-production with a single vcr, often called ADR- "Automated Dialog Replacement" in the film industry.. its also known as a "looping" or "loop session" recording to improve the sound quality of dialogue. Today however this can be acomplished with much greater ease in computer software mixers for working with sound and video.

The legacy effect of "mixing" stereo and mono tracks sources that contain the same content however is not recommended.

So adding two more drum heads brought the total on the drum up to (4 + 2 + 1 = 7) for the video, audio and flying erase head.. and if LP is actually supported (6 + 2 + 1 = 9 heads) .

In the end 4 + 2 +1 was more normal and advertised as 4-head plus HiFi audio plus a "Flying Erase head".. if the product was a high-end model intended for limited Insert Linear video editing between two or more VCRs.. also called "decks"