data recording with analog NTSC

[Michael A. Terrell]

The video recorder couldn't care less about the colour burst - it just
uses to the frame synchs to check that the drum the tape wraps around
is spinning at the right speed.

I've used a number of NTSC color video tape machines that had to have
the color burst to record properly. They had a switch to allow you to
record in B&W by using either its internal burst, or synching to an
external burst signal.

 

[[email protected]]

The ones we worked with - back in 1978 - were not in the least picky.
We certainly didn't bother synthesising a colour burst to add to the
low-line-rate video signal we were recording and playing back on the
video recorders we had.

 

[Michael A. Terrell]

The ones we worked with - back in 1978 - were not in the least picky.
We certainly didn't bother synthesising a colour burst to add to the
low-line-rate video signal we were recording and playing back on the
video recorders we had.

I've used both industrial and professional video recorders. Both
types needed external color burst to function properly. This came from
an external sync generator, or could be synched to another stable video
source, depending on the model.

Low end consumer crap with no time base correction capabilities used
it own color burst signal to generate sync signals. Their performance
was just too poor for our needs.

 

[[email protected]]

Our needs were pretty primitive - the signal we were recording was an
ultrasound image, so there was no colour information at all, and the
ultrasound frequency was either 2MHz or 4MHz which didn't demand much
in the way of time resolution.

One of the video recorders we used was one of the first consumer VHS
machines from JVC. In the lab we used Sony U-matics, with 19mm tape
casettes, but they were a bit bulky when the ultrasound scanner was
being used at a hospital.

We also used a rather more compact open reel machine (AWA - IIRR) with
little bits of reflective tape stuck onto the rim of the take up reel
for an application where we played backed a sequence of scanned images
some twenty-odd times to translate the images into a format that the
cardiologist was used to interpreting. A bit Heath-Robinson/Rube
Goldberg but it worked very reliably.

 

[Mike]

Also, the ---> standard <--- method of solving complex difficult
differential equations IS digital. And HAS BEEN SO FOR THREE CENTURIES!

It is called "Newton's Method".

If an analog solution attempt produces a different result, it is wrong.

Tutorial at http://www.tinaja.com/glib/stalac.pdf

If you wouldn't mind (on, or off list) please explain to me how
Newton's method is _digital_ ? It obviously proceeds by discrete steps
as classically formulated. But it does not depend on computation with
_digits_ and therefore is not digital. Also, it is possible to
construct analog feedback loops which have all the character of
discrete iteration. Such iteration is a special case of continuous
feedback.

Mike

 

[Rich Grise]

On Wed, 28 Sep 2005 11:14:11 -0700, Mike wrote:
[snipped attribution]

If you wouldn't mind (on, or off list) please explain to me how
Newton's method is _digital_ ? It obviously proceeds by discrete steps
as classically formulated. But it does not depend on computation with
_digits_ and therefore is not digital. Also, it is possible to
construct analog feedback loops which have all the character of
discrete iteration. Such iteration is a special case of continuous
feedback.

You're right, there's nothing inherently "digital" about Newton's
method, other than that it's amenable to digital computation, since
number-crunching is involved.

But then again, doesn't an ordinary differential amp or gain stage
"obey" Newton's method (in a manner of speaking) when it "solves"
its own output? ;-)

Cheers!
Rich

 

[Jim Thompson]

On Wed, 28 Sep 2005 11:14:11 -0700, Mike wrote:
[snipped attribution]

If you wouldn't mind (on, or off list) please explain to me how
Newton's method is _digital_ ? It obviously proceeds by discrete steps
as classically formulated. But it does not depend on computation with
_digits_ and therefore is not digital. Also, it is possible to
construct analog feedback loops which have all the character of
discrete iteration. Such iteration is a special case of continuous
feedback.

You're right, there's nothing inherently "digital" about Newton's
method, other than that it's amenable to digital computation, since
number-crunching is involved.

But then again, doesn't an ordinary differential amp or gain stage
"obey" Newton's method (in a manner of speaking) when it "solves"
its own output? ;-)

Cheers!
Rich

That's easy to demonstrate... just add some mild hysteresis to a
linear feedback system, along with a restrictive slew rate.

...Jim Thompson