[Coco] Importing CCRs

[Gene Heskett]

On Saturday 31 March 2007, Kevin Diggs wrote:
>Gene Heskett wrote:
>> Yes I am Art.  The first 'tape' recorders used a rouge coating (to get
>> the iron in a fine grain condition for the higher frequencies) on one
>> side of a 1/4" wide kraft paper tape.  Between the surface roughness
>> of the kraft paper (your basic brown paper bag paper) and the lack of
>> an exciting bias field, the recordings were poorer technically than
>> even todays $10 machine can do.  Head life was often less than 500
>> hours due to the highly abrasive nature of the rouge too.  When the
>> advent of an AC magnetic bias was discovered, which linearized the
>> magnetic properties, the distortion dropped from 80% to 5% in one
>> swell foop, with an accompanying improvement in the noise ratio by
>> about 20 db.  Then it was found that any harmomic distortion in this
>> high frequency bias (running at 80 to 120 khz) also had a pronounced
>> effect on the background hiss and by the time they were done
>> finetuning that and the tape coatings, we have bidirectional stereo
>> recordings at 3.75 ips with 15khz top ends and 60 db snr's.  And
>> distortions were gradually lowered, while peak recording volumes which
>> in the 50's were hard clipped at maybe 6 db above the 2% distortion
>> level, to almost 16db above the 2% distortion levels.  2% was
>> generally where the VU meters were calibrated to show 100%.
>
>You are a bottom less fountain of fascinating facts. Make sure you eat
>plenty of broccoli, carrots, peas and corn. Get a Black & Decker Handy
>Steamer if you have to.

I appreciate the flowers, thanks.  Got one FWIW.

>What is rouge? Is it like rust water?

Rouge is iron oxide, often supplied in a bar form with a wax binder, to be 
applied to a spinning wheel made of many layers of cloth, usually muslin, 
stitched together, and the resultant then used as a fine polishing agent 
on jewelry metals.  Its equivalent grit would be someplace in the 8000 to 
12000+ range.  Its also the main ingredient in facial powders that are 
usually called rouge.  Its not too effective for polishing steels though, 
for that I prefer another stick abrasive that Dico sells, called 
Stainless, which can bring a gun barrel to a mirror finish you could use 
to shave with, usually before washing it up real good and dropping it in 
the hot salts tanks for blueing.  The finish you see in the blue is the 
finish you put in for that most common of blueing treatments.  There are 
other finishes I prefer, one called slow rust coming to mind as its many 
times more durable that hot salts, and doesn't have the flashy 
reflections to spook the game clear into the next drainage when afield 
with ones favorite venison getter.  It also takes several weeks to do 
that finish right, so its not done commercially, ever, unless we're 
talking $20k custom pieces.
>
>What do you think of cassette decks? I have a Realistic SCT-30 3 head
>deck. It is circa 1980 and sounds pretty good. It has a record level
>calibrate (they call it a Dolby calibrate) and a bias fine adjustment
>knob (on the back?). I think it was made by Hitachi. I once found a
>review of it in some magazine. And they said it was an awesome deck.
>Dolby SNR was like 65 and the top end was around 16k. That review raved
>about how hard you had to drive it to saturate it. I have often thought
>of turning off the bias and seeing what the recordings sounded like.

That bias knob was probably a +-20% trim only, to allow one to 
re-establish the performance as the head wears down, until such time as 
the gap between the poles starts to widen, at which point the heads are 
toast.  Those were, and are very good figures indeed, but its the dolby 
that getting you the last 20 db of snr.

As for turning off the bias to see what it sounds like without it?  I 
doubt if you could record anything but an occasional pop since the audio 
itself is typically .2% of the bias level measured at the head terminals, 
its very difficult indeed to see the audio of a few millivolts in the 
presence of 100+ volts rms of bias power.

>Most cassette decks have little dolby symbols at +3 db. Do you know what
>they mean?

See above. In fact I've only worked on 3 or 4 decks that had dolby, and 
calibration was a bear with several sore paws.

>And to get really silly and pointless. What kind of music quality do you
>think you could get if you took Modem modulation techniques and know how
>and tried to do MP3 digital music with a standard analog cassette deck?
>A modern modem connection is about 50 Kbit, right?

Generally speaking yes.  But understand that the modem modulation is a 
very complex tradeoff between the approximately 2400HZ bandwidth of a 
telco connection, and uses some very complex amplitude and phase change 
forms in the modulation in order to get the 56kilobaud through a voice 
grade line.

>A cassette deck is 
>stereo (ignoring cross talk issues). I suspect that a cassette deck also
>has greater fidelity than a phone line (ignoring wow and flutter). Think
>it could do 128 kbit?

I'd think a good cassette deck could probably do that or better, maybe 
even 192k.  And that's on a per track basis.  Stereo is two tracks, so 
the possibility certainly seems to be there.  But be aware that when we 
read or write the disk file of an mp3 using todays computers, that this 
data is commonly read or written in chunks ranging from 32 to 128 bits 
broadside to/from the drive.

This same read or write to the cassette is severely restricted by the 
serial nature of the analog world the tape deals with.

>This is kinda what Philips tried to do with DCC (Digital Compact
>Cassette). Only in my opinion they went in the wrong direction. They
>came out with a new digital gadget that could play analog tapes. They
>should have started with a really good analog deck and did the best they
>could squeezing a digital recording ON A STANDARD TAPE. I have had VERY
>limited success in trying to trick an Optimus DC-2000 into thinking an
>SAQ-X tape is a DCC digital tape. It did work better than trying to get
>a DVHS deck to think a modified normal tape is an SVHS tape. Never seen
>more than a few still pictures with that.

That was pretty poor by broadcast stds although we dd use that SVHS format 
for a few years, but these weren't the $500 memorex's like the shack sold 
or gave away when they couldn't sell them.  We were paying as much as 
$7500 for the best decks.

Both the video snr, and the tape costs due to a limited passcount were its 
downfalls though.

I've never seen one of these DCC tape machines.  If it could play analog 
tapes, then obviously there was no resemblance to a DAT deck, which in 
fact found a much wider use as a cheap tape alternative to the much more 
expensive tape formats normally used for computer backup.  I believe the 
newest version of that can now put 24GB on a DDS5 tape.  When I was using 
DDS2 tapes, I was buying them brand new on ebay for about $2.50/tape.  
The DDS2, with gzip compression could hold around 4GB of average data.  
But the decks themselves were such crap that I eventually gave up, bought 
a 200Gb hard drive and gave 180GB of it to amanda for use as virtual 
tapes.  Litterally 100's of times more dependable and about 1/50th the 
hassle once setup.

>What do you know about back tension?

This is the holdback tension the supply reel normally exerts against the 
tape, and it often is the only source of tension to keep the tape in good 
contact with the heads as the capstan pulls the tape past the heads.

>I bought a Sony DTC-790 DAT deck off eBay. I have not quite gotten it to
>work right. Could the head be bad? If you look at the signal off the
>heads with a scope it is clean for the first 40% of the 90 degree arc.
>But the last part is unstable. Either missing or comes and goes. Think
>it is the head? Or a back tension or alignment issue? I've already
>replaced the pinch roller.

The head is good if you see a good signal for the first 40%.  It was 
probably better off before the roller was replaced.  Tracking adjustments 
in any helical scan format can be a cast iron bitch, and that sounds as 
if the roller is miss-aligned and probably damaging forever, the edge of 
the tape as it is being forced into the guides.  There is a certain 
amount of black magic in getting the pinch rollers to run without pulling 
the tape one way or the other.

>Do you know anything about DVHS?

No, sorry.

>I got one of these off of eBay. It is 
>pretty cool. Kinda like a cross between a VCR and a computer tape deck.
>I looked at the drum once. Don't want to know what it might cost to
>replace that thing. It has ALOT of heads! Though if you think about it I
>don't think the information density is very high on DVHS. Couldn't you
>get 2 hours of HD content on a DDS4 tape? Isn't the native capacity 20G
>for DDS4? Don't know if the data rate is high enough?
>
>kevin

You've seen the head in your dat, then you have an idea what it would look 
like if it was only a few thousanths of an inch over one inch in 
diameter.  And had 6 head tips sticking out of it, each about 20 microns 
wide and 1/16" long.  Don't touch with a finger, they are that easily 
broken.  This is the head in a dvc-pro deck, currently being sold (the 
head and motor as a service part) for about $2700.  I've replaced a 
couple dozen of them, about half due to breakage incurred while cleaning 
them.  Just the guage kit to set one of those up runs about 8 grand.  I 
couldn't stop laughing at a tech in Oklahoma City (Seagate) who did his 
best to convince me the dat head was the pinnacle of the helical head 
art.  Somehow he didn't seem to see the humor in my laughing myself silly 
at some of his 'proclamations'.  The average dat head I've seen shouldn't 
sell for more than a big buck, when I can buy a 6 head vhs head for about 
an 80 dollar bill.  With only 2 heads & 2/3rds the size of a vhs head its 
sheer simplicity and only the smaller quantities should raise the price.

I guess it takes all kinds.

-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
The life which is unexamined is not worth living.
		-- Plato