
Storing data on videotape (1975) - sohkamyung
https://cerncourier.com/from-the-november-1975-issue/
======
adrianmonk
On a similar subject, you may have noticed that the two most common sampling
frequencies for digital audio are 44.1 kHz and 48 kHz (along with their
multiples, such as 88.2 kHz and 96 kHz). Why is that? Specifically, where did
44.1 kHz come from?

It's because early digital audio, before compact discs existed, was done by
recording data onto video cassettes by the use of an adapter that converted
analog audio to digital, then generated a signal that looked (to the videotape
recorder) like a video signal.

In non-interlaced NTSC video, there are 30 frames per second, and 525 scan
lines. But not all 525 are usable because of the vertical blanking interval.
(Essentially that interval is just the time it takes for the CRT to move the
electron beam back up to the top of the display.) So these adapters just
encoded 3 samples' worth of data into a single row of video, and used 490 out
of 525 lines because of the vertical blanking interval. And 3 * 490 * 30 ==
44100, so 44100 samples per second.

NTSC also has an interlaced mode, which is 60 fields per second (two
interlaced fields equal one frame), but each field is half as many lines, so
the math works out the same.

PAL video is similar except that it is 25 frames per second instead of 60, so
to compensate, when encoding audio into PAL video, there are 6/5 as many lines
used, and 3 * 588 * 25 = 44100 as well.

More info:

[https://en.wikipedia.org/wiki/44,100_Hz#Recording_on_video_e...](https://en.wikipedia.org/wiki/44,100_Hz#Recording_on_video_equipment)

~~~
pavlov
Just a nitpick, but NTSC and PAL are always interlaced. They were designed for
CRTs, and so there's no provision in the standards for indicating progressive
frames because it didn't make a practical difference on those display systems.

It became a headache for digital systems, but not until the early to mid 1990s
— before that digital video was usually stored at a half-frame resolution
anyway because the processing power wasn't there for full-frame 480/576 video.

~~~
adrianmonk
Oh, valid nitpick. My reference point for NTSC is whatever my old Amiga and
Commodore 1084s monitor were capable of together, which is based closely on
NTSC/PAL but not exactly the same.

------
chx
[https://en.wikipedia.org/wiki/ArVid](https://en.wikipedia.org/wiki/ArVid)
this was rather popular in certain parts of the world in the early-mid
nineties not just in the former USSR but the former USSR satellite states as
well. Pirated software arrived from Austria weekly on QIC 80 tapes, got copied
to ArVid/VHS in Hungary and sent on to Ukraine and it spread from there. The
gigabytes capacity looked utterly ridiculous at a time when Lands of Lore with
its eight floppies taking a whopping 11 megabytes was a crazy big game.

Later the pirates switched to 2GB DAT tapes and even later hard drives. By the
time I left that world (early 00s), FTP existed, it sure did but there were
quite a bit of problems with both storing and transferring enough so the
weekly packages didn't stop.

~~~
Kadin
Wow. 2GB of uncompressed data per tape is really impressive. That's more than
most of the data-backup tape systems at the time.

I'm surprised/disappointed it never caught on in the US; I would have loved a
backup system like that. But instead we got DAT/DDS, where the cheap recorders
were barely interoperable and the expensive ones cost more than most
individuals could afford. (And I think DDS tapes were under 2GB, in terms of
true capacity and not the shifty advertised capacities.)

I suppose there wasn't enough money in a VHS-based tape system to get any
company interested. Everybody wanted their own proprietary tape format so they
could do the obnoxious razors-and-blades business model, I guess.

~~~
MisterTea
In the 90's I traded warez on Iomega ditto 250MB tapes with a small group of
friends who were active in the BBS warez scene. They would get all the good
stuff, trade, upload and get priority for being a good "upper" (or some such
slang). Every month or so they would release a list. You made a wish list from
that list and handed it in along with a blank tape and a few bucks for chips
and soda. Few days later my friend would collect the tapes and rollerblade to
my place to drop them off on his way home.

------
ohiovr
I bought a little peripheral for my amiga 500 in the 90s that could use a vhs
machine as a data backup. I could store about 100 megabytes on it.
Unfortunately I don’t remember what it was called. It did work ok and it was
really inexpensive I think I paid about $100 for it. The interesting thing to
me was how simple the electronic guts of it were. No flat packs or long dips.

~~~
pronoiac
What the VHS backups would look like if you watched them:

Amiga Video Backup System:
[https://youtube.com/watch?v=1jrLz__PlM0](https://youtube.com/watch?v=1jrLz__PlM0)

Danmere Backer:
[https://youtube.com/watch?v=TUS0Zv2APjU&t=13m30s](https://youtube.com/watch?v=TUS0Zv2APjU&t=13m30s)

~~~
avian
Interesting that these all look black-and-white. I'm guessing using VHS's low-
bandwidth chroma channels for additional capacity wasn't worth the added
complexity.

~~~
ohiovr
Indeed ntsc does not have a lot of bandwidth devoted to chroma. Color on
broadcast tv was tacked on about a decade after it was established. If you
look at the signal on an oscilloscope only a small part is for chroma. I think
it is called chroma burst.

------
m-i-l
On a slightly related note, I used to use a hi-fi stereo equipped VHS (used
for recording NICAM digital stereo transmissions) to listen to music, e.g.
transferring my vinyl albums to VHS tape. Advantages (beyond protecting the
original vinyl) included:

\- Quality - the audio format used for recording NICAM audio was vastly
superior to that of audio cassettes.

\- Capacity - you could easily fit a double concept album on one tape so no
interruptions flipping the record over, or even in many cases have an artist's
entire back-catalogue on a single tape.

\- Indexing - on my video recorder you could even record index points on the
tape, so when you had several albums on one tape you could forward/rewind to
the start of the album relatively easily.

~~~
sborra
That's super neat. What kind of VCRs support NICAM audio?

~~~
opencl
Like most fancy VCR features NICAM decoders started out as an expensive high
end thing in the late 80s and gradually trickled down to lower price points.
Note that there were no VCRs that recorded audio in the NICAM format, only
decoded it.

The actual recording mechanism was VHS Hi-Fi, which uses helical scanning to
record a relatively high quality analog stereo track onto the tape vs the
normal not-very-good VHS mono audio track that uses a stationary read/write
head.

In the late 90s D-VHS came out which recorded digital MPEG video and audio
onto VHS tapes (and supported high definition 720p/1080i!) but it was an
extremely expensive niche thing that never took off in any meaningful way.

------
sohkamyung
Original (PDF) article from CERN News can be read at [1]

[1] [https://cds.cern.ch/record/1729841](https://cds.cern.ch/record/1729841)

