Απο αυτα που εχω διαβασει, το θεμα hdmi δεν ειναι απλο. Τουλαχιστον οσο απλο ακουγετε ενα "ψηφιακο σημα" 0100111010001.
Απο αυτα που εχω ακουσει, ειναι οτι ΕΧΕΙ διαφορα και στα ματια και ειναι και μετρησιμη. Αυτα απο ατομα που εμπιστευομαι και τα ματια τους και τα οργανα τους.....
Επι της ουσιας και για οποιον ενδιαφερετε, ριξτε μια καλη ματια στο παρακατω κειμενο που ειναι δημοσιευμενο σε εταιρια που κατασκευαζει και διαθετει ΜΕΤΡΗΤΗ, στις εταιριες για να ελεγχουν τα καλωδια τους.
There are many aspects influencing the performance of any given HDMI cable or accessory, such as an HDMI switch or distribution device. Put your geek glasses on! The following represents just a few of the measured elements that comprise the Digital Performance Level (DPL) ranking system:
Bandwidth — The aggregate bandwidth requirement for HDMI Version 1.3a Category 2 is listed at 10.2 Gbps.
This value is the sum of the individual color, data, and audio lines contained within the HDMI cable. More HDMI “dynamic headroom” will be needed above that to take it to even higher resolutions.
Low bandwidth decreases the available resolution and or the color depth.
Capacitance/Dielectric loss — High capacitance and dielectric loss causes
video frequency response issues and corrupted data on the data communication channels (DDC). This is caused by the proximities of the individual wires within the cable to each other and the dielectric materials between them.
Current for the supply line — The current required to pass the Hot Plug and EDID (Extended Display Identification Data) information between the source and the display.
A weak current causes this handshaking to fail.
The HDMI standard specifies a minimum of 55 mA drain on the voltage supply lines for handling the Hot Plug feature and the passing of EDID information between the source and the sink. Some of the “active repeaters” built into HDMI cables draw their power from this same line. If the amplifier circuitry draws 100mA or more, which most do, and is used with a weak source current, the handshaking used during the creation of the connection and in maintaining it likely will fail due to the fact that it is not a requirement for all manufacturers to provide the high current required by such devices.
Display Data Channel (DDC) Corruption — EDID and HDCP (High-bandwidth Digital Content Protection for digital rights management) data are passed as part of the constant handshaking process between the source and the display.
DDC data corruption is the largest cause of the connection having problems or not working at all.
Video quality can downgrade or even change in color if DDC is corrupted. With some systems, any DDC corruption can cause the unit to fail totally.
HDCP needs to refresh about every 2 seconds. If the system does not get this refresh, it surely will die.
DDC-I2C (Inter-Integrated Circuit) — This electrical bus supplies all of the intelligence to the system.
The clock signals used for the data transfers must match the timing of the data precisely.
Delay — The timing of the serialized signals varies for the individual conductors within an HDMI cable.
If these individual delays fall outside of the “wiggle room” for the specification, the clock timing fails to operate correctly and failures occur.
Eye Pattern — This is the popular “Cat’s Eye” pattern shown in ads for many of the better cables on the market. T
he pattern visually depicts the electrical characteristics of the entire data transmission: output voltage, frequency response, jitter, noise, timing, and even the probability of its working well. It is a good indicator of the overall quality of a cable and how well it actually will work.
A “mask margin” is inserted into the actual signal reflecting the HDMI minimum compliance spec as a base for comparison. This margin is a percentage measurement. The key is to see how much performance over and above the spec’s margin is achieved and, in some cases, negative margin (or non-compliance).
The left photo shows a near perfect eye at 1080i for one of the vendors tested at the DPL labs—notice how wide the white space is. The middle photo shows the eye for the same length at 1080i for a different manufacturer. Although both products pass the eye test with flying colors, the right cable would be the first one to fail when pushing for higher resolution (1080p) or longer distance (or if it is installed improperly). The left cable would get a higher DPL ranking than the left. If they cost about the same, which one would you buy? Needless to say, the cable on the right is “in the dirt.” It may work, but there is a high probability it will be unreliable. It would receive a low DPL rank.
Impedance — All wires exhibit resistance to the voltage being carried across it. To produce a perfect non reflective transmission line, load impedance must match the HDMI impedance of 100 Ohms. If there is not constant 100-Ohm impedance, the longer the cable, the more the performance of the signal is degraded.
Intra Pair Skew — The individual pairs of cables within the HDMI cable itself are twisted to eliminate noise and establish the operating impedance (balanced pair signaling).
The tolerance of the twists drastically affects the timing of the signals running across them. If they are not completely symmetrical, one wire ends up being the slightest bit longer than the other.
This means that the signal from one wire arrives the tiniest bit later than the other one, which could cause enough duty-cycle distortion to create bit-errors.
Inter Pair Skew — The timing between each of the balanced pairs of wires within the cable. They all must be twisted, laid, and cut precisely to reduce any length differences.
Again, if the signal of one pair arrives even the tiniest bit later than another, it could destroy the signal.
Intra- and inter-pair skew: Some cables tested at the DPL labs were over 300 thousandths of an inch off in timing, meaning the individual wires vary too much in length.
Jitter — Changes in the timing of the signals over time. Due to tolerances and variances in the signal propagations, the signal characteristics vary, which affect the timing. J
itter is measured in picoseconds and has a very low tolerance.
Πηγη.....
http://www.cepro.com/article/new_program_will_certify_rank_hdmi_cables_distributor_adi_is_on_board/
m2c
