glen herrmannsfeldt wrote:
> Les Cargill <lcargill99@comcast.com> wrote:
>
> (snip, I wrote)
>>> When NTSC came out, as far as I know it, black and white was still
>>> supposed to be 15750Hz. Video recorders should be able to do either
>>> one, and obviously need at least some tolerance.
>
>>> As far as actually writing CDs, the unit block is 1/75 of a second.
>
>>> I am not quite sure how video recorders work on non-video signals.
>
>> The HiFi track is (was?) borrowed from the top video line and isn't
>> strictly linear.
>
>> "VHS Hi-Fi recovers the depth-recorded AFM signal by subtracting the
>> audio head's signal (which contains the AFM signal contaminated by a
>> weak image of the video signal) from the video head's signal (which
>> contains only the video signal), then demodulates the left and right
>> audio channels from their respective frequency carriers."
>
> I had a Beta Hi-Fi VCR long before I had VHS,

As did I. It was a stunning unit.

Strange thing; as an object lesson, the president of the company I 
worked for then loaned one to every employee. You kept it as long as you 
worked there.

I wonder what he did with them all?


> and Beta always
> seemed to work better. For Beta, they just moved the video
> (luminance) signal up and put a new carrier in the space.
> No extra head.
>


The "extra head" would be the "linear audio" track ( with
lousy resolution and quite noisy)?

> It seems that Beta allows for the playback device to track
> the FM carrier even if it moves, but VHS doesn't.

Right. I mixed an album or two to VHS hifi and you had
to have something locked to NTSC for it to work.

One poor schmoe had "The Execution of Private Slovik"
for the video.

> (I believe
> this also complicated the copy protection systems.)
> So, instead, VHS uses this depth recording method, where the
> HiFi audio track is recorded deep into the tape, and the video
> signal on top. I didn't know about the subtraction.
>

FWIW, I always heard they "borrowed" the top video line and it was 
demuxed with time slicing magic.

>> The "PCM to video adapters" like the F1 just did some sort of encoding
>> to video frames using all that bandwidth. Quite buffered I am sure;
>> I'd guess to a multiple of the frame rate.
>
>> One of my instructors in college invented a doohickey that would allow
>> you to back up your IBM PC to VHS like that.
>
> Yes. But what, exactly, is the timing? How many bits per scan line,
> and lines per field?
>

I'm pretty sure the 44.056 rate covers it.

http://recordingtheworld.infopop.cc/eve/forums/a/tpc/f/222604446/m/3656003463

Not the best exposition I've seen but it covers the basics. Somebody,
somewhere had to do samplerate conversion between 44.1 and 44.056; oy!


>>> Can you record during vertical sync?  (Given that there is no actual
>>> retrace to do.)  For Beta and VHS, they have to do a head switch,
>>> I believe every frame.
>
>> Something like that. HiFi would tick at times; I always figured
>> that was the head switch.
>
> I never notice the tick, but maybe I didn't listen carefully.
> I believe both Beta and VHS uses FM carriers.

Right. Hence the "not quite linear". I had sort of forgotten the FM
part.

> If the heads are
> aligned right, it should make a nice transition, but there will
> likely be a discontinuity in the phase of the carrier.
>
>>> There is likely a discontinuity when that
>>> happens. Having the nice fraction means you can phase lock, even
>>> if you don't write every line.
>
> -- glen
>

In a handful of years, nobody will remember any of these technologies.

-- 
Les Cargill

Les Cargill <lcargill99@comcast.com> wrote:

(snip, I wrote)
>> When NTSC came out, as far as I know it, black and white was still
>> supposed to be 15750Hz. Video recorders should be able to do either
>> one, and obviously need at least some tolerance.

>> As far as actually writing CDs, the unit block is 1/75 of a second.

>> I am not quite sure how video recorders work on non-video signals.

> The HiFi track is (was?) borrowed from the top video line and isn't 
> strictly linear.

> "VHS Hi-Fi recovers the depth-recorded AFM signal by subtracting the
> audio head's signal (which contains the AFM signal contaminated by a
> weak image of the video signal) from the video head's signal (which
> contains only the video signal), then demodulates the left and right
> audio channels from their respective frequency carriers."

I had a Beta Hi-Fi VCR long before I had VHS, and Beta always
seemed to work better. For Beta, they just moved the video 
(luminance) signal up and put a new carrier in the space.
No extra head. 

It seems that Beta allows for the playback device to track
the FM carrier even if it moves, but VHS doesn't. (I believe
this also complicated the copy protection systems.) 
So, instead, VHS uses this depth recording method, where the 
HiFi audio track is recorded deep into the tape, and the video
signal on top. I didn't know about the subtraction.

> The "PCM to video adapters" like the F1 just did some sort of encoding
> to video frames using all that bandwidth. Quite buffered I am sure;
> I'd guess to a multiple of the frame rate.

> One of my instructors in college invented a doohickey that would allow 
> you to back up your IBM PC to VHS like that.

Yes. But what, exactly, is the timing? How many bits per scan line,
and lines per field?

>> Can you record during vertical sync?  (Given that there is no actual
>> retrace to do.)  For Beta and VHS, they have to do a head switch,
>> I believe every frame.

> Something like that. HiFi would tick at times; I always figured 
> that was the head switch.

I never notice the tick, but maybe I didn't listen carefully.
I believe both Beta and VHS uses FM carriers. If the heads are
aligned right, it should make a nice transition, but there will
likely be a discontinuity in the phase of the carrier. 

>> There is likely a discontinuity when that
>> happens. Having the nice fraction means you can phase lock, even
>> if you don't write every line.

-- glen

glen herrmannsfeldt wrote:
> robert bristow-johnson <rbj@audioimagination.com> wrote:
>> On 5/7/15 9:36 PM, Steve Pope wrote:
>
> (snip)
>>> The scenario that some Sony engineers designed the F1 to fit
>>> in with a Betamax machine, ending up with a 44.1 KHz sample rate
>>> for semi-random reasons,
>
>> one might be that 44100 Hz = 14/5 * 15750 Hz.
>
>> the 44056 comes from the slightly reduced horizontal freq due to the
>> NTSC color standards.
>
> When NTSC came out, as far as I know it, black and white was still
> supposed to be 15750Hz. Video recorders should be able to do either
> one, and obviously need at least some tolerance.
>
> As far as actually writing CDs, the unit block is 1/75 of a second.
>
> I am not quite sure how video recorders work on non-video signals.

The HiFi track is (was?) borrowed from the top video line and isn't 
strictly linear.

"VHS Hi-Fi recovers the depth-recorded AFM signal by subtracting the
audio head's signal (which contains the AFM signal contaminated by a
weak image of the video signal) from the video head's signal (which
contains only the video signal), then demodulates the left and right
audio channels from their respective frequency carriers."

The "PCM to video adapters" like the F1 just did some sort of encoding
to video frames using all that bandwidth. Quite buffered I am sure;
I'd guess to a multiple of the frame rate.

One of my instructors in college invented a doohickey that would allow 
you to back up your IBM PC to VHS like that.

> Can you record during vertical sync?  (Given that there is no actual
> retrace to do.)  For Beta and VHS, they have to do a head switch,
> I believe every frame.

Something like that. HiFi would tick at times; I always figured that was 
the head switch.

> There is likely a discontinuity when that
> happens. Having the nice fraction means you can phase lock, even
> if you don't write every line.
>
> -- glen
>

-- 
Les Cargill

robert bristow-johnson <rbj@audioimagination.com> wrote:
> On 5/7/15 9:36 PM, Steve Pope wrote:

(snip)
>> The scenario that some Sony engineers designed the F1 to fit
>> in with a Betamax machine, ending up with a 44.1 KHz sample rate
>> for semi-random reasons,

> one might be that 44100 Hz = 14/5 * 15750 Hz.

> the 44056 comes from the slightly reduced horizontal freq due to the 
> NTSC color standards.

When NTSC came out, as far as I know it, black and white was still
supposed to be 15750Hz. Video recorders should be able to do either
one, and obviously need at least some tolerance.

As far as actually writing CDs, the unit block is 1/75 of a second.

I am not quite sure how video recorders work on non-video signals.
Can you record during vertical sync?  (Given that there is no actual
retrace to do.)  For Beta and VHS, they have to do a head switch,
I believe every frame. There is likely a discontinuity when that
happens. Having the nice fraction means you can phase lock, even
if you don't write every line.

-- glen

On 5/7/15 9:36 PM, Steve Pope wrote:
> robert bristow-johnson<rbj@audioimagination.com>  wrote:
>
>> On 5/6/15 9:42 PM, rickman wrote:
>
>>> I don't think the fact that it was Beta vs. VHS had anything to do with
>>> it. I think the sample rate is linked to the TV rates which are the same
>>> for both. There were early digital recordings on VCRs and the CD sample
>>> rate was set to be compatible.
>
>> but the Sony F1 *was* a betamax device, as i recall.  i realize that the
>> same video can be recorded on a VHS.  i just dunno how the box was.
>
> The scenario that some Sony engineers designed the F1 to fit
> in with a Betamax machine, ending up with a 44.1 KHz sample rate
> for semi-random reasons,

one might be that 44100 Hz = 14/5 * 15750 Hz.

the 44056 comes from the slightly reduced horizontal freq due to the 
NTSC color standards.

> and then Sony managers forced some
> hapless unrelated group of Sony engineers supporting the CD Red Book
> standards effort to insist upon a 44.1 KHz sample rate ...

there were also Phillips engineers involved.

> against their better judgement ... entirely believable.



-- 

r b-j                  rbj@audioimagination.com

"Imagination is more important than knowledge."

On Thu, 07 May 2015 20:42:21 -0400, robert bristow-johnson
<rbj@audioimagination.com> wrote:

>On 5/7/15 8:59 AM, Greg Berchin wrote:
>> As I understand it, single-precision IEEE 754 floating point has 24 bit
>> precision with 23 fractional bits explicitly stored. Were you referring
>> to a different single-precision format?
>
>hidden one *and* sign bit plus 23.  even without the scaling of floating 
>point, an IEEE single-precision float can exactly represent 2^25 
>different signed integers.  maybe it's 2^25 + 1 with zero.

Understood. I guess it may be 2^25 + 5 if you count &#4294967295;infinity and two
types of NaN. (Yeah, I had to take a little IEEE 754 refresher course
this morning.)

glen herrmannsfeldt  <gah@ugcs.caltech.edu> wrote:

>Steve Pope <spope33@speedymail.org> wrote:

>> robert bristow-johnson  <rbj@audioimagination.com> wrote:
> 
>>>On 5/6/15 9:42 PM, rickman wrote:
> 
>>>> I don't think the fact that it was Beta vs. VHS had anything to do with
>>>> it. I think the sample rate is linked to the TV rates which are the same
>>>> for both. There were early digital recordings on VCRs and the CD sample
>>>> rate was set to be compatible.
> 
>>>but the Sony F1 *was* a betamax device, as i recall.  i realize that the 
>>>same video can be recorded on a VHS.  i just dunno how the box was.
> 
>> The scenario that some Sony engineers designed the F1 to fit
>> in with a Betamax machine, ending up with a 44.1 KHz sample rate
>> for semi-random reasons, and then Sony managers forced some 
>> hapless unrelated group of Sony engineers supporting the CD Red Book
>> standards effort to insist upon a 44.1 KHz sample rate ...
>> against their better judgement ... entirely believable.
>
>I suppose, but there weren't many choices for CD master making back
>then. 

>Nine track tape is 150MB at 6250BPI, none of the current high
>density tape systems existed. People were actually starting
>to use video tape as computer backup systems.

>I don't know the exact numbers, but a block size and block rate
>that allows for easy writing to NTSC video is pretty convenient.

For certain market players, yes.  Going on memory -- Sony, and also Ampex 
were wedded to pre-existing helical scan data recorders.  Whereas 3M came 
out with a 48 ksample/sec tape system, eventually in multitrack (transverse
scan?). I think it was market-dominant for awhile (well, 6 months anyway), 
and it was for an interval of time the right choice, a dedicated 
digital audio recorder.  

(Am I misremembering this?)


Steve

Steve Pope <spope33@speedymail.org> wrote:
> robert bristow-johnson  <rbj@audioimagination.com> wrote:
 
>>On 5/6/15 9:42 PM, rickman wrote:
 
>>> I don't think the fact that it was Beta vs. VHS had anything to do with
>>> it. I think the sample rate is linked to the TV rates which are the same
>>> for both. There were early digital recordings on VCRs and the CD sample
>>> rate was set to be compatible.
 
>>but the Sony F1 *was* a betamax device, as i recall.  i realize that the 
>>same video can be recorded on a VHS.  i just dunno how the box was.
 
> The scenario that some Sony engineers designed the F1 to fit
> in with a Betamax machine, ending up with a 44.1 KHz sample rate
> for semi-random reasons, and then Sony managers forced some 
> hapless unrelated group of Sony engineers supporting the CD Red Book
> standards effort to insist upon a 44.1 KHz sample rate ...
> against their better judgement ... entirely believable.

I suppose, but there weren't many choices for CD master making back
then. 

Nine track tape is 150MB at 6250BPI, none of the current high
density tape systems existed. People were actually starting
to use video tape as computer backup systems.

I don't know the exact numbers, but a block size and block rate
that allows for easy writing to NTSC video is pretty convenient.

-- glen