HDMi lead Version 1.4 vs. 2.0
 

Wanting to buy a couple of HDMi leads for an upgrade following upgrade
of TV which is UHD/4K and 3D.

As we all known buying HDMi leads is difficult already with the v1.3
ones on length, quality and prices. Price not being a guide at all to
quality.

I see some as being version 1.4 quoted as being for 4K and 3D
Others as being 2.0 and also for 4K and 3D. ( These look to be flat
cable and not round.)
Have seen some quoting to be version 1.4/2.0

Length wise 1.5 mtr would be ok but might just go for 2 mtr to be safe.

Does the version I buy matter is the question? (Price matters in the
fact I do not want to pay say Currys rip of prices.)

Thanks
David

HDMi lead Version 1.4 vs. 2.0
 

David wrote:
As we all known buying HDMi leads is difficult already

I've never found it difficult ... go to Tesco, take "Value HDMI Lead" to
till, go home.

I see some as being version 1.4 quoted as being for 4K and 3D
Others as being 2.0 and also for 4K and 3D.

What source do you have for 4K and/or 3D material?

From the HDMI licensing website ...

"HDMI 2.0 does not define new cables or new connectors. Current High
Speed cables (Category 2 cables) are capable of carrying the increased
bandwidth."

So any v1.4 cable marked "High Speed" or claiming 1080p should be fine.

HDMi lead Version 1.4 vs. 2.0
 

On 17/01/2015 14:49, Andy Burns wrote:
David wrote:
As we all known buying HDMi leads is difficult already

I've never found it difficult ... go to Tesco, take "Value HDMI Lead" to
till, go home.

I see some as being version 1.4 quoted as being for 4K and 3D
Others as being 2.0 and also for 4K and 3D.

What source do you have for 4K and/or 3D material?


3D Blu-ray and I understand the streaming sites such as Netfix will be
offering 4K material.
Regards
David

HDMi lead Version 1.4 vs. 2.0
 

David wrote:

Andy Burns wrote:

What source do you have for 4K and/or 3D material?

3D Blu-ray

Should be fine with that "out of the box"

and I understand the streaming sites such as Netfix will be
offering 4K material.

Presumably you'll need to upgrade to a 4K capable video card?

HDMi lead Version 1.4 vs. 2.0
 

On 17/01/2015 16:05, Andy Burns wrote:
David wrote:

Andy Burns wrote:

What source do you have for 4K and/or 3D material?

3D Blu-ray

Should be fine with that "out of the box"

and I understand the streaming sites such as Netfix will be
offering 4K material.

Presumably you'll need to upgrade to a 4K capable video card?




a number of 4k televisions already have 4k netflix streaming built in.
it's debatable whether streamed 4k would look better than a HD blu ray
with higher bitrate though.

--
Gareth.
That fly.... Is your magic wand.

HDMi lead Version 1.4 vs. 2.0
 

Which no broadband will be able to cope with soon in any case.
Save us from over development of systems please.
Brian

--
From the Sofa of Brian Gaff Reply address is active
"David" wrote in message
...
On 17/01/2015 14:49, Andy Burns wrote:
David wrote:
As we all known buying HDMi leads is difficult already

I've never found it difficult ... go to Tesco, take "Value HDMI Lead" to
till, go home.

I see some as being version 1.4 quoted as being for 4K and 3D
Others as being 2.0 and also for 4K and 3D.

What source do you have for 4K and/or 3D material?


3D Blu-ray and I understand the streaming sites such as Netfix will be
offering 4K material.
Regards
David

HDMi lead Version 1.4 vs. 2.0
 

Brian Gaff wrote:

Which no broadband will be able to cope with soon in any case.

Netflix apparently say 25 Mbps is required for 4K streaming.

HDMi lead Version 1.4 vs. 2.0
 

On 18/01/2015 11:24, Andy Burns wrote:
Brian Gaff wrote:

Which no broadband will be able to cope with soon in any case.

Netflix apparently say 25 Mbps is required for 4K streaming.

Got more than that.
Regards
David

HDMi lead Version 1.4 vs. 2.0
 

Just thought of something else to ask, once out the wrapper can one tell
if it is V1.3, 1.4 or 2.0?
Regards
David

HDMi lead Version 1.4 vs. 2.0
 

In article , David wrote:
Just thought of something else to ask, once out the wrapper can one tell
if it is V1.3, 1.4 or 2.0? Regards David

I'd be interested in the answer to that, and related aspects of HDMI
cables. I've recently found swapping around different cables affected
behaviour of devices. Albeit with pretty cheap cables. And in at least one
case I suspect the cable is not 'fully populated' with no sign of this on
the package.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

HDMi lead Version 1.4 vs. 2.0
 

On 19/01/2015 09:46, Jim Lesurf wrote:
In article , David wrote:
Just thought of something else to ask, once out the wrapper can one tell
if it is V1.3, 1.4 or 2.0? Regards David

I'd be interested in the answer to that, and related aspects of HDMI
cables. I've recently found swapping around different cables affected
behaviour of devices. Albeit with pretty cheap cables. And in at least one
case I suspect the cable is not 'fully populated' with no sign of this on
the package.

Jim



Who is in charge of the HDMI specifications etc.?
Beginning to look like a really big mess to me.
Regards
David

HDMi lead Version 1.4 vs. 2.0
 

Jim Lesurf wrote:

David Park wrote:

once out the wrapper can one tell
if it is V1.3, 1.4 or 2.0? Regards David

I'd be interested in the answer to that, and related aspects of HDMI
cables.

I don't think there's been any change of cable spec 1.3-1.4-2.0 merely
that if the cable is "High Speed" it should cope with the higher
resolutions/frame rates/3D etc, except I think the "HDMI with Ethernet"
variety needs a particular cable.

HDMi lead Version 1.4 vs. 2.0
 

In article , Andy
Burns
wrote:
Jim Lesurf wrote:

David Park wrote:

once out the wrapper can one tell
if it is V1.3, 1.4 or 2.0? Regards David

I'd be interested in the answer to that, and related aspects of HDMI
cables.

I don't think there's been any change of cable spec 1.3-1.4-2.0 merely
that if the cable is "High Speed" it should cope with the higher
resolutions/frame rates/3D etc, except I think the "HDMI with Ethernet"
variety needs a particular cable.


The only spec doc I have details a bandwidth / freqency response for the
cable. Can't recall what HDMI version it is. , but I'll check. I assume the
later specs demand a higher bandwidth.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

HDMi lead Version 1.4 vs. 2.0
 

On 19/01/2015 14:05, Andy Burns wrote:
Jim Lesurf wrote:

David Park wrote:

once out the wrapper can one tell
if it is V1.3, 1.4 or 2.0? Regards David

I'd be interested in the answer to that, and related aspects of HDMI
cables.

I don't think there's been any change of cable spec 1.3-1.4-2.0 merely
that if the cable is "High Speed" it should cope with the higher
resolutions/frame rates/3D etc, except I think the "HDMI with Ethernet"
variety needs a particular cable.




i certainly had an otherwise perfectly fine working hdmi lead that
refused to work with ARC - an equally cheap one that mentioned 1.4
worked though.

--
Gareth.
That fly.... Is your magic wand.

HDMi lead Version 1.4 vs. 2.0
 

the dog from that film you saw wrote:

Andy Burns wrote:

I don't think there's been any change of cable spec 1.3-1.4-2.0 merely
that if the cable is "High Speed" it should cope with the higher
resolutions/frame rates/3D etc, except I think the "HDMI with Ethernet"
variety needs a particular cable.

i certainly had an otherwise perfectly fine working hdmi lead that
refused to work with ARC - an equally cheap one that mentioned 1.4
worked though.

I thought the only pin differences for 1.4 concerned HEC (HDMI ethernet
channel) on pins 14&19, but it seems ARC shares those pins.

HDMi lead Version 1.4 vs. 2.0
 

Andy Burns wrote:
the dog from that film you saw wrote:

Andy Burns wrote:

I don't think there's been any change of cable spec 1.3-1.4-2.0 merely
that if the cable is "High Speed" it should cope with the higher
resolutions/frame rates/3D etc, except I think the "HDMI with Ethernet"
variety needs a particular cable.

i certainly had an otherwise perfectly fine working hdmi lead that
refused to work with ARC - an equally cheap one that mentioned 1.4
worked though.

I thought the only pin differences for 1.4 concerned HEC (HDMI ethernet
channel) on pins 14&19, but it seems ARC shares those pins.

Too lazy to look myself, but for 1.3 and 1.4 questions the answers may
lie here -

https://docs.google.com/folderview?i...&usp=drive_web

HDMi lead Version 1.4 vs. 2.0
 

In message , Andy
Furniss writes
Andy Burns wrote:
the dog from that film you saw wrote:

Andy Burns wrote:

I don't think there's been any change of cable spec 1.3-1.4-2.0 merely
that if the cable is "High Speed" it should cope with the higher
resolutions/frame rates/3D etc, except I think the "HDMI with Ethernet"
variety needs a particular cable.

i certainly had an otherwise perfectly fine working hdmi lead that
refused to work with ARC - an equally cheap one that mentioned 1.4
worked though.

I thought the only pin differences for 1.4 concerned HEC (HDMI ethernet
channel) on pins 14&19, but it seems ARC shares those pins.

Too lazy to look myself, but for 1.3 and 1.4 questions the answers may
lie here -

https://docs.google.com/folderview?i...6cFNPTEU&usp=d
rive_web

Bloody 'ell! 237 pages and 425 pages! Just as well HDMI isn't
complicated.
--
Ian

HDMi lead Version 1.4 vs. 2.0
 

In article ,
Jim Lesurf wrote:

The only spec doc I have details a bandwidth / freqency response for the
cable. Can't recall what HDMI version it is. , but I'll check. I assume the
later specs demand a higher bandwidth.

No. There isn't a difference between cables for different version
numbers. That is, there's no such thing as an HDMI 1.2 cable for
example. However there are "standard" and "high speed" cables. The
former are supposed to support up to 720p/1080i, the latter up to 4k.
All are supposed to support ARC, but in my experience not all work
reliably.

(There are also the cables that include ethernet.)

-- Richard

HDMi lead Version 1.4 vs. 2.0
 

On 20/01/2015 11:12, Richard Tobin wrote:
In article ,
Jim Lesurf wrote:

The only spec doc I have details a bandwidth / freqency response for the
cable. Can't recall what HDMI version it is. , but I'll check. I assume the
later specs demand a higher bandwidth.

No. There isn't a difference between cables for different version
numbers. That is, there's no such thing as an HDMI 1.2 cable for
example. However there are "standard" and "high speed" cables. The
former are supposed to support up to 720p/1080i, the latter up to 4k.
All are supposed to support ARC, but in my experience not all work
reliably.

(There are also the cables that include ethernet.)

-- Richard

Well Richard that is just as confusing as I was when I posted my
confused original post.

Ok which work reliably for all situations that you found?

(I have ordered two which say they are V2.0)
Regards
David

HDMi lead Version 1.4 vs. 2.0
 

In article , Richard Tobin
wrote:
In article , Jim Lesurf
wrote:

The only spec doc I have details a bandwidth / freqency response for
the cable. Can't recall what HDMI version it is. , but I'll check. I
assume the later specs demand a higher bandwidth.

No. There isn't a difference between cables for different version
numbers.

So what do the different version number actually relate to?

BTW The only document I currently have is an Hitachi spec for version
'1.3a'.

That is, there's no such thing as an HDMI 1.2 cable for
example. However there are "standard" and "high speed" cables. The
former are supposed to support up to 720p/1080i, the latter up to 4k.
All are supposed to support ARC, but in my experience not all work
reliably.

(There are also the cables that include ethernet.)

I recently encountered a situation where I'd bought two cheap HDMI cables
from different shops.

Using one of them to connect a DVD recorder to the TV I found that the TV
didn't 'detect' the recorder being switched on and used. So I experimented
with swapping over that cable with one I'd been using between one of my
computers and its monitor. (Also for 1920 x 1080 at 50Hz.)

The cable I'd been using for the computer allowed the recorder to get the
TV to notice when it was switched on and used. So now they worked together
according to the handbooks.

From which I assume that the cheap cable either has some connections
missing or has some other imperfection/limitation.

Experimenting with it between computer and monitor I found that it removed
a problem I'd had. In the past a specific image as 'wallpaper' acquired a
green tinge for some near-black pixels when using a paericular screen mode.
With the new, cheap, cable, this effect had gone and the image looked fine.
No tinge any more.

So the real question is how you can tell when seeing a cable what it will
behave like in a given use, and what actual abilities it supports.

Looking at the electronic spec I can see that the HDMI could easily cause
such device-varying quirks. e.g. the signal cables aren't 'matched' to the
cable at the source end. So if they mismatch the destination load, fun can
begin. As it may if the pairs, etc, are imperfect.

The challenge then being to know before you buy which cables are without
such problems *without* them being high priced gold-plated ones onto which
someone has sprinkled oofle dust.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

HDMi lead Version 1.4 vs. 2.0
 

In article , David wrote:
Ok which work reliably for all situations that you found?

An Amazon Basics cable:

http://www.amazon.co.uk/gp/product/B003L1ZYYM

-- Richard

HDMi lead Version 1.4 vs. 2.0
 

In article ,
Jim Lesurf wrote:

No. There isn't a difference between cables for different version
numbers.

So what do the different version number actually relate to?

Things other than cables.

http://www.audioholics.com/hdtv-form...-hdmi-versions

-- Richard

HDMi lead Version 1.4 vs. 2.0
 

On 20/01/2015 15:23, Richard Tobin wrote:
In article , David wrote:
Ok which work reliably for all situations that you found?

An Amazon Basics cable:

http://www.amazon.co.uk/gp/product/B003L1ZYYM

-- Richard

This is what I received today from ordering yesterday.
http://www.ebay.co.uk/itm/151483249128
Look good quality and working ok.
Regards
David

HDMi lead Version 1.4 vs. 2.0
 

In article , Richard Tobin
wrote:
In article , Jim Lesurf
wrote:

No. There isn't a difference between cables for different version
numbers.

So what do the different version number actually relate to?

Things other than cables.

http://www.audioholics.com/hdtv-form...-hdmi-versions

So essentially worthless/irrelevant as a way to tell one cable from
another.

Which leads back to my main question when faced with finding that cables do
vary in what works with them. How to determine if one will do a task from
the sales blurb, etc. Looks like "plug and prey" rules...

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

HDMi lead Version 1.4 vs. 2.0
 

Jim Lesurf wrote:

Richard Tobin wrote:

There isn't a difference between cables for different version
numbers.

So what do the different version number actually relate to?

The protocol that's run over it, I've got some nice IPv6 compatible
Ethernet leads if anyone's interested, they also support jumbo frames!

HDMi lead Version 1.4 vs. 2.0
 

"Jim Lesurf" wrote in message
...
In article , Richard Tobin
wrote:
In article , Jim Lesurf
wrote:

No. There isn't a difference between cables for different version
numbers.

So what do the different version number actually relate to?

Things other than cables.

http://www.audioholics.com/hdtv-form...-hdmi-versions

So essentially worthless/irrelevant as a way to tell one cable from
another.

Which leads back to my main question when faced with finding that cables
do
vary in what works with them. How to determine if one will do a task from
the sales blurb, etc. Looks like "plug and prey" rules...

You could try

http://www.russandrews.com/product.a...ZZBNCMNGRPOLLP

--
JohnT

HDMi lead Version 1.4 vs. 2.0
 

On 21/01/2015 12:40, JohnT wrote:



You could try

http://www.russandrews.com/product.a...ZZBNCMNGRPOLLP



ROFL

Well I'm using 3 X 2 mtr which would be £1,113.60

Possibly more than the average price of a TV set.

Regards
David

HDMi lead Version 1.4 vs. 2.0
 

In article ,
Jim Lesurf wrote:

So what do the different version number actually relate to?

Things other than cables.

http://www.audioholics.com/hdtv-form...-hdmi-versions

So essentially worthless/irrelevant as a way to tell one cable from
another.

That's a bit of a stranage way to put it. The HDMI cables that don't
work are ones that don't conform to the standard, and you can hardly
expect the standard to classify cables that don't conform to it.

-- Richard

HDMi lead Version 1.4 vs. 2.0
 

On 20/01/2015 20:00, Andy Burns wrote:

I've got some nice IPv6 compatible
Ethernet leads if anyone's interested, they also support jumbo frames!

Wouldn't they get stuck if the bend radius was too sharp ?


--
Mark
Please replace invalid and invalid with gmx and net to reply.

HDMi lead Version 1.4 vs. 2.0
 

In article , Richard Tobin
wrote:
In article , Jim Lesurf
wrote:

So what do the different version number actually relate to?

Things other than cables.

http://www.audioholics.com/hdtv-form...-hdmi-versions

So essentially worthless/irrelevant as a way to tell one cable from
another.

That's a bit of a stranage way to put it. The HDMI cables that don't
work are ones that don't conform to the standard, and you can hardly
expect the standard to classify cables that don't conform to it.

See the problem I outlined earlier.

Two cables behaving differently. One 'cured' the problem between a TV and a
recorder, the other 'cured' the problem between a monitor and a computer.
Neither worked correctly in the other application.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

HDMi lead Version 1.4 vs. 2.0
 

In article ,
Jim Lesurf wrote:

That's a bit of a stranage way to put it. The HDMI cables that don't
work are ones that don't conform to the standard, and you can hardly
expect the standard to classify cables that don't conform to it.

See the problem I outlined earlier.

Two cables behaving differently. One 'cured' the problem between a TV and a
recorder, the other 'cured' the problem between a monitor and a computer.
Neither worked correctly in the other application.

I quite agree that there's a problem with many HDMI cables not working
properly. Either the cables or the devices are not meeting the
standard.

-- Richard

HDMi lead Version 1.4 vs. 2.0
 

On 22/01/2015 10:30, Jim Lesurf wrote:
Two cables behaving differently. One 'cured' the problem between a TV and a
recorder, the other 'cured' the problem between a monitor and a computer.
Neither worked correctly in the other application.

Your symptoms are just weird. Dropped bits on a digital comms link
causing a green cast to the picture?

I wonder if it had fallen back to some kind of analogue mode.

Andy

HDMi lead Version 1.4 vs. 2.0
 

In article ,
Vir Campestris wrote:

Two cables behaving differently. One 'cured' the problem between a TV and a
recorder, the other 'cured' the problem between a monitor and a computer.
Neither worked correctly in the other application.

Your symptoms are just weird. Dropped bits on a digital comms link
causing a green cast to the picture?

I wonder if it had fallen back to some kind of analogue mode.

HDMI cables don't have any analogue connection.

HDMI can use various colour spaces; perhaps a faulty connection caused
the two ends to disagree about which one to use.

-- Richard

HDMi lead Version 1.4 vs. 2.0
 

In article , Vir
Campestris wrote:
On 22/01/2015 10:30, Jim Lesurf wrote:
Two cables behaving differently. One 'cured' the problem between a TV
and a recorder, the other 'cured' the problem between a monitor and a
computer. Neither worked correctly in the other application.

Your symptoms are just weird. Dropped bits on a digital comms link
causing a green cast to the picture?

Yes, it did make me think at the time of the old H2G2 business of being
beyond 'surprise' and having to resort to 'astonishment'. :-) Until it
happened I'd assumed that tales of HDMI leads affecting the result in such
ways must be fancyful. However there it was.

On the same system some screen modes give other kinds of image defects. I
can only guess, but the ideas that came to me we

1) Some kind of clock synch skew problem with parallel bit transmissions
over the three data pairs arriving 'out of synch' and changing some colour
values.

2) ditto for edge effect ringing (mismatch to the cables) confusing the
receiver.

3) crosstalk between the data pairs causing some values to be altered when
received depending on the patterns of other pairs.

From the document I have, I can see that HDMI transfer *isn't* impedance
matched at both ends of the cable. They define the load at the destination,
but the input is essentially a 'current sink or float' - i.e. 'high
impedance'. Hence any mismatch between cable impedance and destination
could play havoc with the voltage and current levels sloshing back and
forth. And in turn aggrivating crosstalk.

So whilst 'bits is bits' there remains the problem of correctly receiving
the levels to determine correctly the bits sent. The bits aren't 'dropped'
so much as the RX simple interprets some of them incorrectly.

And the behaviour will depend on how well a particular cable impedance
matches a given monitor/TV input impedance. Also may depend on how much
the signal pairs are bent or squashed together, altering their impedances
and any crosstalk levels. Laid out straight the cables may be OK. squashed
and bent, maybe not.

In theory, theory and practice agree. But in practice... :-)

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

HDMi lead Version 1.4 vs. 2.0
 

On Sun, 25 Jan 2015 11:09:18 +0000 (GMT), Jim Lesurf
wrote:

In article , Vir
Campestris wrote:
On 22/01/2015 10:30, Jim Lesurf wrote:
Two cables behaving differently. One 'cured' the problem between a TV
and a recorder, the other 'cured' the problem between a monitor and a
computer. Neither worked correctly in the other application.

Your symptoms are just weird. Dropped bits on a digital comms link
causing a green cast to the picture?

Yes, it did make me think at the time of the old H2G2 business of being
beyond 'surprise' and having to resort to 'astonishment'. :-) Until it
happened I'd assumed that tales of HDMI leads affecting the result in such
ways must be fancyful. However there it was.

On the same system some screen modes give other kinds of image defects. I
can only guess, but the ideas that came to me we

1) Some kind of clock synch skew problem with parallel bit transmissions
over the three data pairs arriving 'out of synch' and changing some colour
values.

2) ditto for edge effect ringing (mismatch to the cables) confusing the
receiver.

3) crosstalk between the data pairs causing some values to be altered when
received depending on the patterns of other pairs.

From the document I have, I can see that HDMI transfer *isn't* impedance
matched at both ends of the cable. They define the load at the destination,
but the input is essentially a 'current sink or float' - i.e. 'high
impedance'. Hence any mismatch between cable impedance and destination
could play havoc with the voltage and current levels sloshing back and
forth. And in turn aggrivating crosstalk.

When it comes to _unidirectional_ transmission line systems, it's
only the recieving end that needs to be matched. Provided this is the
case, there will _not_ be any reflection of energy back from the
matched load to trouble the mismatched sending end to cause additional
reflections.

The more predictable mismatched sending impedance is usually chosen
to be low to make it look like a voltage source. The only time it
might make sense to use high impedance constant current sources is
when you wish to combine the outputs of several sources in parallel in
a simple additive summing of signals into the feeder cable.

When the signals being sent are _all_ serialised for transmission
over a single transmission line, the crosstalk problem simply doesn't
exist.

I'm not fully acquainted with the HDMI spec but I can't imagine it
making any sense to use more than a single balanced pair for each
direction of transmission of the digital video signals.

Assuming HDMI supports a 'back channel' for full digital video
return, as long as the rule, "Match the recieving end only" is
applied, the two balanced pairs could be laid up as a quad pair,
saving on unnecessary shielding between the pairs (reserving any such
cable shielding as a common shield for the whole cable).

I'm no expert on HDMI so my 'assumptions' that the designers made
commonsense use of the lessons of "Communications 101" could be
totally wrong (it really aught to be a 'no brainer' to get this sort
of thing absolutely spot on by now).

As for the weird effects sometimes experienced with HDMI connections,
they won't be due to cable issues if good engineering practice has
been followed in formulating the cabling standard. Since the spec
concentrates on matching the receiving end impedance to the cable
impedance, there's a strong suggestion that, for once, the standards
committee do have a fuller understanding of transmission cabling
requirements suggesting that the issues may be more to do with
mishandling of the protocols rather than cable defects.
--
J B Good

HDMi lead Version 1.4 vs. 2.0
 

In article , Johny B Good
wrote:
On Sun, 25 Jan 2015 11:09:18 +0000 (GMT), Jim Lesurf
wrote:


When it comes to _unidirectional_ transmission line systems, it's only
the recieving end that needs to be matched. Provided this is the case,
there will _not_ be any reflection of energy back from the matched load
to trouble the mismatched sending end to cause additional reflections.

Yes, that's all wonderful as theory. Alas, in reality the receiver is
unlikely to precisely match the cable. We're talking domestic consumer
goods here and five-ten quid cables bent and squashed behind the equipment.

So in the real world, as soon as the rx end reflects we will find that the
gross mismatch at the tx end will bounce back most of that again. Whereas
if the tx end was reasonably matched it would eat a fair bit of it
following the first reflection.

The result is a degrading of the waveform shapes at the rx end which is
somewhat bigger than if the tx end was matched to some reasonable extent.

And it means a tendency for some of the energy from one bit in the serial
sequence to be delayed and presented to the rx later on. Perhaps affecting
its ability to reliably understand the next bit correctly.


The more predictable mismatched sending impedance is usually chosen to
be low to make it look like a voltage source. The only time it might
make sense to use high impedance constant current sources is when you
wish to combine the outputs of several sources in parallel in a simple
additive summing of signals into the feeder cable.

And open (high) and closed (low) source will both reflect almost all that
comes back to them. So in this respect a near-zero source (voltage assert)
is as bad as a near-open (current source/sink). They both have a reflection
coefficient whose magnitude approaches unity.


When the signals being sent are _all_ serialised for transmission over
a single transmission line, the crosstalk problem simply doesn't exist.

The HDMI cable has *three* paired-line-in-shield connections running in
parallel to shovel the data across. This is to cope with the sheer rate of
data transfer.


Assuming HDMI supports a 'back channel' for full digital video return,
as long as the rule, "Match the recieving end only" is applied, the two
balanced pairs could be laid up as a quad pair, saving on unnecessary
shielding between the pairs (reserving any such cable shielding as a
common shield for the whole cable).

Alas, people tend to assume that we have things like balanced parallel
pairs and shields and treat them as if in a textbook.

Easy to forget that, say, putting something right up against such a system
can affect its behaviour or that a shield only works when matched and thick
enough. And that any physical distortions also alter behaviour.

Mismatch at the tx end can also mean some currents bounced back up the
*outside* of the 'shield'.

Real World != Undergrad Textbook Theory returns TRUE here, alas.



As for the weird effects sometimes experienced with HDMI connections,
they won't be due to cable issues if good engineering practice has been
followed in formulating the cabling standard.

IF statement duly noted. :-)

Alas reality may not match theory, any more than these sources match their
cables. The real world seems happier with "fling the problem over the
fence". i.e. here "assume the rx is matched regardless of whatever cable
you got and how much you've bent or squashed it."


Since the spec
concentrates on matching the receiving end impedance to the cable
impedance, there's a strong suggestion that, for once, the standards
committee do have a fuller understanding of transmission cabling
requirements suggesting that the issues may be more to do with
mishandling of the protocols rather than cable defects.

I beg to differ. :-)

I assume you do realise, BTW that real wideband cables tend to have an
impedance that is frequency dependent. Somehow I doubt all HDMI cables are
adjusted to meet the Heavyside requirement, even ignoring the presence of
other cables right beside them, etc.

I fear that in reality the people making these cables and systems are more
reliant on "Its digital, innit!" - i.e. taking advantage of the ability of
digital systems to ignore small alterations in waveform shapes, etc. Alas,
this has its limits.

I can see that the HDMI designers have tried to play some useful tricks.
e.g. the balanced pair clearly is aimed to have a constant internal total
current within each shield. That - if achieved - will help reduce problems
like crosstalk, for example. The problem is that this may not help with the
above problems. And relies on accurate synchrony with a tx that is
mismatched by choice.

Jim

--
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