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Topic:
Weird HDMI issues - Imagine that !
This thread has 112 replies. Displaying posts 76 through 90.
Post 76 made on Sunday June 13, 2010 at 21:21
Audible Solutions
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On June 13, 2010 at 20:27, crosen said...
I specifically seek to verify whether an AVR repeats inbound video as is (timing issues and all) to the display, or whether there is an element of signal restoration. I'm sure you will agree this is important information for a CI.

No the AVR does not repeat data. There is not signal restoration. It is not important.

(I have been told that there is no signal restoration from the AVR. However, I have also been told that there is no encryption on the TMDS stream. It clearly makes sense to vet any assertion :-)

There is none

You apparently do not see the connection between how encryption is handled over the HDMI links and whether the AVR creates a new stream. However, I have presented an argument that there is a connection, and that through this connection it becomes apparent that the AVR does, in fact, perform an element of signal restoration.

Worry about what matters. There is no new data stream.

Here is argument, again, in a more brief form:

a. if the video stream on the inbound link to the AVR is encrypted using a different set of keys from the video stream on the outbound link from the AVR, then the two video streams do not consist of the same bits. Agreed?

b. also: if the video stream on the inbound link to the AVR does not consist of the same bits as the video stream on the oubound link from the AVR to the display, then the AVR is not simply repeating the inbound link. Rather, it is creating a new one. Agreed?

c. it follows that: if the video stream on the two links are encrypted using different keys, then the AVR is not simply repeating the first link. Agreed?

I believe both a. and b. are true. That means c. is true.

Right or wrong?

I give up.
"This is a Christian Country,Charlie,founded on Christian values...when you can't put a nativiy scene in front fire house at Christmas time in Nacogdoches Township, something's gone terribly wrong"
Post 77 made on Sunday June 13, 2010 at 22:46
phil
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crosen
I think what you are trying to say is that if I encrypt data using Key"A" and then encrypt the same data using Key "B", then while encrypted the the 2 encrypted data streams do not consist of the same 1s and 0s because different Keys were used.

But when both are decrytped the data is identical.


When HDMI is thrown into the mix the 1s, and 0s are different when between the source-to-AVR compared to the 1s and 0s when they are between the AVR and sink. But when decrypted both are the same, and if they are the same why would this matter?
"Regarding surround sound, I know musicians too well to want them behind my back."
-Walter Becker
Post 78 made on Sunday June 13, 2010 at 23:24
crosen
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On June 13, 2010 at 22:46, phil said...
crosen
I think what you are trying to say is that if I encrypt data using Key"A" and then encrypt the same data using Key "B", then while encrypted the the 2 encrypted data streams do not consist of the same 1s and 0s because different Keys were used.

Yes, excatly.

But when both are decrytped the data is identical.

Yes.

When HDMI is thrown into the mix the 1s, and 0s are different when between the source-to-AVR compared to the 1s and 0s when they are between the AVR and sink.

Yes, and therefore it seems logical to conclude that the AVR is not simply "passing through" the stream from its input (i.e. from the source) to the output (i.e. to the sink.) Rather, it would seem that the AVR is creating a fresh, new stream of bits.

This seemingly logical conclusion (i.e. that the AVR is creating a fresh, new stream of bits (with fresh timing and voltage levels) when sending video to the display) runs counter to what everybody here seems to be saying. I am trying to figure out where the truth lies.

But when decrypted both are the same, and if they are the same why would this matter?

Well, the significance of all this that I'm focused on is whether the encryption proves that the AVR is creating a new bit stream with fresh timing and voltage levels. I know I'm having trouble conveying this idea clearly.

All I'm saying is that if the 1s and 0s are different when between the source-to-AVR compared to the 1s and 0s when they are between the AVR and sink, then the AVR is obviously creating a new bit stream to send to the sink.

I just want an "expert" to either verify that this is true, or else point out the flaw in logic that makes it appear true to me.  Brent, Audible Solutions, Bob, et al all say it is not true.  I don't have an explanation about where there is a flaw in the logic, though.
If it's not simple, it's not sufficiently advanced.
Post 79 made on Monday June 14, 2010 at 02:39
mariomp
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What is this HDMI thing you guys are talking about for 6 pages now?
Is this something I will need to go and learn about? :-)
Post 80 made on Monday June 14, 2010 at 13:58
crosen
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Brent - can you do me (and possibly all of us) a favor, and ask Jeff B what is meant when Denon says in their HDMI product literature that their AVR's are "Repeaters" and not "Switchers?" Thanks.

[Link: usa.denon.com]
If it's not simple, it's not sufficiently advanced.
Post 81 made on Monday June 14, 2010 at 14:15
mr2channel
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Crosen,

Since Brent is a very busy fella and has quite a bit on his plate I thought I would help you out....give these guys a call [Link: usa.denon.com] and then maybe try [Link: dpllabs.com] that should get you in touch with the right people.
What part of "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed." do you not understand?
Post 82 made on Monday June 14, 2010 at 14:16
Brentm
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This one I do not need Jeff for.

Switchers have no ability to do anything with the signal (such as extract audio or add analog to HDMI upconversion).
Brent McCall
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Ethereal (386) 846-7264 Cell
Post 83 made on Monday June 14, 2010 at 14:56
crosen
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On June 14, 2010 at 14:16, Brentm said...
This one I do not need Jeff for.

Switchers have no ability to do anything with the signal (such as extract audio or add analog to HDMI upconversion).

Well, I think it means more than that. I think the full answer speaks directly to whether th hdmi signals sent out from the avr have new timing, etc. I understand that you are busy. Maybe I can gather some info that the community here can benefit from (eventhough most are convinced it is only I who needs this education :-)
If it's not simple, it's not sufficiently advanced.
Post 84 made on Monday June 14, 2010 at 15:56
Brentm
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I have passed this onto Jeff, he will (I hope) read to night and comment.
Brent McCall
Paid Endorser for;
Ethereal (386) 846-7264 Cell
Post 85 made on Monday June 14, 2010 at 16:27
crosen
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On June 14, 2010 at 15:56, Brentm said...
I have passed this onto Jeff, he will (I hope) read to night and comment.

That's great. Thank you.
If it's not simple, it's not sufficiently advanced.
Post 86 made on Monday June 14, 2010 at 22:47
BobL
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A little background info, almost 30 years ago (Damn am I getting that old) I worked for IBM as a technician working on Mainframe computers. 8b/10b was very new back then and used to connect drives to the mainframe computers. For perspective these drives were the size of washing machines.

Back in those days we would change out a board that needed to be replaced and then go back to the shop diagnose the problem and repair the board to be used in another repair if needed. Today boards are disposable.

A good technician not only knew his job but also knew when the problem needed expertise above his level. Back then we would call the chip and board designers. Today they also have a sub-specialty called integrity engineers.

How does this relate? First 8b/10b is the predecessor to DVI/HDMI. They just have more capabilities, faster speeds and HDCP but the basics are very similar. Second, I am NOT an expert but have a good understanding of the basics. Just wanted to make that clear.

Ok next post!
Post 87 made on Monday June 14, 2010 at 23:16
BobL
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Keys! Keys! Keys! There seems to be some confusion with keys and I want to try to simplify some of this.

Authentication Keys - This is sent by the source, the display receives it and applies an equation and sends back the answer. If the answer is good the next step begins. This is done on the DDC channel. When you read about Key selection Vector (KSV) this is what it refers to, not encryption keys. Repeaters have to identify themselves, some require keys and others don't. I'm not sure what determines if a key is required by a repeater and not just identified.

Device Keys - The number of devices the source allows up to 127 with 7 different levels (ie repeater type devices).

Encryption/cypher keys - This is what is needed to decode the TMDS data. TMDS data is encrypted if the source requires HDCP otherwise it is not. This is needed to prevent "man in the middle" from getting the data. A circuit board could be made that just read the data streams but didn't touch the DDC line and placed between two devices and the data could be stolen easily without encryption.

Now I am not sure where this key is generated and on which line it originates. HDCP uses a stream cipher, so my guess is the key is transmitted at the beginning of the data. Again, I am not sure and it really doesn't matter. But if you want more info on stream ciphers here is a link from wikipedia.
[Link: en.wikipedia.org]

Stream ciphers are a basic form of encryption, similar to locking your car but having no alarm on it. It will keep only basic thieves away.

Next post.
Post 88 made on Tuesday June 15, 2010 at 00:31
BobL
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Data and electronics.

Does the AVR pass along the data or re-transmit the stream? A repeaters function is to re-transmit the data. If there is no OSD or video processing than the data is simply re-transmitted and I assume re-clocked.

If there is OSD or video processing than and it is entirely new data that is sent because each frame/field is not the same as the original from the source.

Why does an AVR cause problems when there is none when going direct from the source to display?

A number of reasons can exist for this. But, let's keep the first part of this simple. The AVR isn't as tolerant of an out of spec signal. For example a cable box is putting out 3.5 volts. The TV accepts anything with 3.3 volts or higher. The AVR goes by the spec and only accepts signals by HDMI minimum spec of 4.7 volts. When you add the AVR you have no picture, is it the AVRs fault? Of course not! But, since we have no inexpensive way of testing this stuff our logic tells us it is.

Another problem is electronics. A "1" in binary is nothing more than positive voltage. So to make a "1" we turn on the voltage. I'll use 5 volts and seconds for example.

We turn on 5 volts and we keep it on 1 second, and then turn it off. This creates a square wave. Our receiving device needs see at least 4.7 volts for .95 seconds before it receives the "1" otherwise we get no picture.

If we have too much resistance in the circuit that voltage will be reduced and the receiver won't be see the wave and we will get no picture.

If we have too much capacitance in the circuit it takes longer for the voltage to go from 0 to 5 volts. This is called the rise time. So now the first line of our "square" wave is curved instead of going straight up. On an oscilloscope this looks like what I call a shark fin. Now at 4.7 volts the wave is not long enough to see if for .95 seconds and we get no picture.  Now remember this is all being done in billionths of a second and not .95 seconds.

These problems can happen anywhere in the chain of equipment and there can be cumulative problems within a circuit if not well designed.  So it doesn't matter if the receiver is re-transmitting the data if there is a problem with the circuit.

There are of course other problems that can happen. EMI/ RF interference, crosstalk, timing errors such as inter-pair skew because so far we have only talked about 1 channel of data, etc.

Hope this helps or maybe Jeff can give a better description.  I'm done for tonight.

Bob
Post 89 made on Tuesday June 15, 2010 at 00:57
phil
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I think where crosen is going with this is that IF the AVR takes the incoming TMDS data, decrypts it and then re encrypts it to send it to the sink, the new encrypted signal should be a good 5vpp data stream at the point it leaves the AVR, provided the incoming signal was ok and the AVR was working properly. This would indicate a restoration of a marginal signal from a cable box, say 4.8vpp back up to 5vpp.
If the above were true then when the cable box direct to the TV was good but bad when run thru the AVR it would indicate a problem with the AVR or the 2nd HDMI cable. The cumulative cable/connector db loss would be restored somewhat by the AVR if it is a restorer.

If, as many here have stated, the data from the cable box goes thru the AVR untouched (unrestored) it would complicate troubleshooting an HDMI problem.

Brent in post 8 said that sub 1k AVRs DO NOT rebuild signal level and indicated that more expensive units do. This would change what happens to HDMI inside AVRs and also change the troubleshooting of problems with HDMI based on model.

Is there a specification on an AVR that would tell how it handles HDMI?
"Regarding surround sound, I know musicians too well to want them behind my back."
-Walter Becker
Post 90 made on Tuesday June 15, 2010 at 01:03
crosen
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Does the AVR pass along the data or re-transmit the stream?

That is the million dollar question!

A repeaters function is to re-transmit the data. If there is no OSD or video processing than the data is simply re-transmitted and I assume re-clocked.

Even if there is no OSD and no video processing, if the AVR is playing audio from the stream, then it is not just retransmitting the video data it receives to the display.  Rather, it is created a new stream.

How do we know this?

We know this because the stream received by the AVR from the source is encrypted by the source using the key of the AVR.  (If that weren't so, then the AVR would not be able to strip out the audio.) If the AVR simply passed along the stream it received from the source, the display would not be able to decrypt it.  So, the AVR must change the stream into one that is encrypted using key information from the display.  So, the AVR is sending a different stream to the display than it received from the source.

Ergo, new data, new timing and new voltage!
If it's not simple, it's not sufficiently advanced.
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