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Discussion Starter · #1 ·
Short Version: Tech Support at Monoprice has recommended using a minimum of 4' HDMI cables (as opposed to using, say, 2' or 3' cables), even as interconnects between components / receivers. The Reason given was that "it takes 4 ft for HDMI signal to reach maximum strength again." I couldn't find any individual corroboration of this, so I turned here.




Longer Version: I currently have a setup like this...


Components (PS3, etc.) -- -- Mits HC6800 Projector


Video processing on the Onkyo is off, so it should be passthrough. I use the PS3 as my Blu Ray player, and even with the 50' cable directly connected from the receiver to the projector, I occasionally get handshake issues and signal dropouts when using the PS3 (movies in 1080p and sometimes even games in 720p.)


I was considering replacing the 50' cable with one of Monoprice's HDMI over Cat6 STP solutions, and was going to use 1' HDMI cables at each end when I got the advice from them about using a minimum of 4' HDMI cables, which I found surprising.


So, any and all input is welcomed. If you think the Cat6 solution is worth trying (or not) and have any experience with it, I'm interested. Of course, I'm also interested in the "minimum HDMI cable" question.


Thanks!
 

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Quote:
Originally Posted by pintozack /forum/post/20811498


Short Version: Tech Support at Monoprice has recommended using a minimum of 4' HDMI cables (as opposed to using, say, 2' or 3' cables), even as interconnects between components / receivers. The Reason given was that "it takes 4 ft for HDMI signal to reach maximum strength again." I couldn't find any individual corroboration of this, so I turned here.




Longer Version: I currently have a setup like this...


Components (PS3, etc.) -- -- Mits HC6800 Projector


Video processing on the Onkyo is off, so it should be passthrough. I use the PS3 as my Blu Ray player, and even with the 50' cable directly connected from the receiver to the projector, I occasionally get handshake issues and signal dropouts when using the PS3 (movies in 1080p and sometimes even games in 720p.)


I was considering replacing the 50' cable with one of Monoprice's HDMI over Cat6 STP solutions, and was going to use 1' HDMI cables at each end when I got the advice from them about using a minimum of 4' HDMI cables, which I found surprising.


So, any and all input is welcomed. If you think the Cat6 solution is worth trying (or not) and have any experience with it, I'm interested. Of course, I'm also interested in the "minimum HDMI cable" question.


Thanks!

The 50' for high speed can be problematic. Do you have Deep Color off? If you don't that could solve your problems (maybe). If Deep Color is already disabled, then yes a Cat 6 solution should provide an improvement in signal integrity.


The 1' versus 4' question is outside of my knowledge. Sorry.
 

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Basically, what they are "quoting" is the need to have "some minimum length" of cabling that is likely related to the "need" for a "standard transmission interface" that has some form of "line build out" in its design. That "buildout" has minimums that it expects to "see" when looking out at the cable.... basically it provides a "matching" for impedances to provide "optimum" transmission to prevent "overly hot" OR highly reflection conditions.
 

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Discussion Starter · #5 ·

Quote:
Originally Posted by alk3997 /forum/post/20811963


The 50' for high speed can be problematic. Do you have Deep Color off? If you don't that could solve your problems (maybe).

Andy, thanks for your reply. I will check tonight whether deep color is off or auto, although I suspect it is on. I have seen quite a few people say that deep color is all hype -- do you think it's something people generally don't notice? (Of course, I'll try it for myself.)


Also, do you happen to know if deep color would also be output when playing games via PS3 or is that only for Blu Ray movies? Thanks!
 

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Discussion Starter · #6 ·

Quote:
Originally Posted by budwich /forum/post/20812493


Basically, what they are "quoting" is the need to have "some minimum length" of cabling that is likely related to the "need" for a "standard transmission interface" that has some form of "line build out" in its design. That "buildout" has minimums that it expects to "see" when looking out at the cable.... basically it provides a "matching" for impedances to provide "optimum" transmission to prevent "overly hot" OR highly reflection conditions.

So... ah... I take it you don't subscribe to that theory in a practical application?
 

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No I didn't say that. In "real world transmission communication standards" (ie. strict telecommunications applications), design spec's are "well-defined" for a given interface (eg. long haul transmission, short haul, etc). Every manufacturer that expects his equipment to be used in the network publishes them AND follows them. In alot of cases, their interfaces are "switchable" in terms of the "line build out" because no one "fixed design" will meet the optimum conditions. Of course, they could do a similar thing in the HDMI world BUT the need and expense would not warrant it since "most applications" could/would probably fall between X and Y feet where X is some "small" number and Y is some large number. The large number is probably in that 30-35 foot range while the small number ... well... take your guess ... 1 foot, 2 foot, 3 foot ???? The problem is that most equipment makers don't publish their spec and thus the "best guess" of what their design is... is what I think they are quoting.... BUT there is a design spec (in the manufacturer's domain either internally and / or external) but I don't believe it is a "gold standard" like the equipment telecom industry standards. These are JUST consumer pieces where no one really cares if it works exactly as designed... just as long as it kind of works.... :)
 

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I work in the industry and there is no minimum length. If HDMI used pre-emphasis on its transmitters then possibly you might have a minimum length to knock down some of the pre-emphasized signal before it reaches an input. But pre-emphasis is not allowed for HDMI.


I can test HDMI signals direct from the output ports of a source device and there are no issues with the signal though it does not go through some minimum length of HDMI cable. The large, 50Ω single-ended cables I use to run to the oscilloscope match the impedance of the source traces and the loading at the oscilloscope so reflections are not an issue. I also use 1.5ft HDMI cables at work all the time to connect signal break-out boards together and they work fine.


I have to say that running 50ft of HDMI cable without an equalizer (booster) at the end is a little scary. I would try an equalizer before going with CAT5/6.
 

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Haven't seen a need for a Minimum

Output cable length on the units we work with (we have 0.5m cables throughout various test rigs) - though I guess if your supplier says the kit they supply requires it your best to follow the advice.


A powered HDMI Extender up at the Projector is another option for you to consider.


Very few BD Discs are encoded in Deep Color and likewise only a few games - switch on Deep Color with 99% of BD Discs and your seeing the wrong colours!


Joe
 

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Quote:
Originally Posted by Joe Fernand /forum/post/20816081


Very few BD Discs are encoded in Deep Color

0, since Blu-ray only supports 8-bit color. Even Deep Color test content is hard to find.
 

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Discussion Starter · #14 ·
Thank you all for the very valuable feedback and background info.


I haven't had a chance yet to try without deep color, but that will be my first test. (Hey, I have a 10 month old... My schedule is not my own.) Although I am concerned that that's not the only issue since I got dropouts while playing a 720p game on the PS3, and I don't think games are transmitted with deep color, but I'll gladly be told otherwise.


But I am now considering first trying an extender before the Cat6 solution. Awhile back I did try the Monoprice extender 2849, which claims to be powered via the 5V on HDMI itself, and it did nothing -- actually added enough insertion loss to kill the signal. Anyone have experience with either of their other extenders that can use external power: 7700 or 8120? Or another reasonably priced one that works well?
 

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Discussion Starter · #15 ·
Things get stranger... I swapped the cable between the PS3 and the Onkyo AVR from a 4ft to a 6ft (both 24 AWG) and unless it's wishful thinking, the 6ft is doing better. Maybe the 4ft was straining a connection (even though there seemed to be slack)?


The PS3 did have Deep Color enabled (Automatic), so I disabled that. I can report through limited testing that with Deep Color on, the PS3 always output 12-bit/channel (a.k.a. 36-bit) color, whether it was showing a Blu Ray or playing a game -- even games in 720p.


I only know this by enabling the video processor on the Onkyo, which reported "36-bit" color. With Deep Color disabled, it reported "24-bit" but was then itself sending "30-bit" out to the projector. I normally have the video processor disabled altogether, so hopefully it sends the 24-bit color unmodified and doesn't change it to 30-bit. No way I could find for the projector to say what it's receiving.


Disabling Deep Color seems to have stabilized video output (in my short test; no dropouts) although longer tests will tell us for sure. I'll keep plugging away... Thanks again.
 

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to answer OP's orig question about min cable length, yes, a min length can be derived from the known tranceiver specs along with the characteristics of the cable being used. i dunno what min length for hdmi 1.3 is. just like ethernet the transceivers are sensitive to Fex and Nex (far and near end cross talk). too short of cable will take Fex and Nex to a level the transceiver cant handle thus creating errors. and keep in mind, not all transceivers are built well, etc.


4ft min is a good suggestion for 10Gb via twisted pair copper, but it all depends on cable design and the transceivers involved.
 

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Discussion Starter · #17 ·

Quote:
Originally Posted by Denon_Kid /forum/post/0


4ft min is a good suggestion for 10Gb via twisted pair copper, but it all depends on cable design and the transceivers involved.

I guess the problem in a general practical sense, though, is that for most consumer equipment, as far as aware, these types of specifications are not published, as someone mentioned above. I'm guessing there's concern on manufacturer's parts that publishing things like min and max cable lengths would overwhelm consumers -- and then there's the notion that they couldn't guarantee those min/max values are accurate with all equipment or cables (because again, those specs aren't published.)
 

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As I stated above there is no minimum length for HDMI cables. Denon_Kid, there are large differences between 10G Ethernet and HDMI. HDMI is a single direction signal (speaking of the high-speed TMDS signals) so transceivers are not involved. There are HDMI transmitters and HDMI receivers. Because of this, far end cross-talk and near end cross-talk is not an issue with HDMI. All TMDS signal travel from source to sink and experience similar attenuation. HDMI connectors have well controlled impedance through them so reflections are minimal and the TMDS pairs are supposed to be individually shielded so crosstalk within the cable is minute. FYI
 

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Quote:
Originally Posted by FiberOpticDude /forum/post/20831117


As I stated above there is no minimum length for HDMI cables. Denon_Kid, there are large differences between 10G Ethernet and HDMI. HDMI is a single direction signal (speaking of the high-speed TMDS signals) so transceivers are not involved. There are HDMI transmitters and HDMI receivers. Because of this, far end cross-talk and near end cross-talk is not an issue with HDMI. All TMDS signal travel from source to sink and experience similar attenuation. HDMI connectors have well controlled impedance through them so reflections are minimal and the TMDS pairs are supposed to be individually shielded so crosstalk within the cable is minute. FYI

nex and fex is not defined only by the transmitter/receiver pair, its a inherent issue that depends on cable length, construction type, frequency, etc etc. when you say "single direction signal" doesnt the 1.4a spec allow for bi-directional digital data flow, so doesnt this mean a 1.4a hdmi port is a transceiver, or does the return audio portion gets transmitted/received by some other device that is wired into the hdmi port??? 1.4a is not a "single direction" signal in the cable, and tmds is a form of lvds which means you have current flows in both directions with the differential cml on the receiver side (current loop).


i am not 100% up on the signaling. i suspect hdmi is parallel tmds to achieve the ~10Gb rate?
 

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I have tested many HDMI cables, transmitters, and receivers over the last few years and never been able to see any crosstalk whatsoever on the TMDS signal lines. The shielding and connector design of HDMI mitigates this issue. I have seen crosstalk between the SDA and SCL wires of the DDC link on poor quality HDMI cables that twist the SDA and SCL wires together (dumb, dumb, dumb). Note that these wires are not shielded. I have tried to convince a specific Chinese cable manufacturers not to twist these wires together but they believe they must. Well... at least until they experience customer issues with HDCP signals unable to properly handshake on their longer cables!


HDMI 1.4a allows for a low data-rate audio return channel (ARC) to travel to on a wire pair in the cable, and I do believe that they use a separate IC for receiving the ARC signal. I have never heard anyone in the industry use the term transceiver related to HDMI. The data rate of the audio return channel approximately 1000x lower in data rate than the TMDS signals. Also TMDS signals are NOT a form of LVDS. They are a form of CML signaling. The design and specifications of LVDS Tx and Rx devices is very different than that of CML devices. If you would like to learn more about HDMI please check out the DVI specs from which HDMI was based:

http:/ www.ddwg.org/lib/dvi_10.pdf


Transition Minimized Differential Signaling (TMDS) is 4 differential pairs of approx. 1Vp-p amplitude. They are DC coupled from open-collector sources to 50Ω pull-ups attached to 3.3V on the receiver. Three of the pairs are for DATA and one is a CLOCK signal (D0, D1, D2, CLK). A couple of data rates are 1.485Gbps each channel for 1080p @ 60Hz standard color (24bit) and 2.23Gbps for 1080p @ 60Hz with deep color (36bit).


Note that the Display Data Channel (DDC) signals on an HMDI cable are bi-directional making use of an I2C interface. Note that this type of communication only has one side talking at a time. The HDCP signals travel via DDC. As noted above I have seen crosstalk between the SDA and SCL wires which is due to coupling between the wires in a cable with these wires twisted together. Note that this type of crosstalk gets worse as the cable gets longer, so the shorter the better.


Cheers
 
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