How HDMI Works

HDMI Signals

One of the common misperceptions about HDMI is that the digital signal is innately superior to an analog signal. In some people's minds, the lack of analog-digital conversion means that the signal is in a pure, undamaged state when it reaches the HDTV. It's easy to imagine a high-definition, digital signal traveling straight from an HD-DVD player to an HDTV. But signal transmission via HDTV does require an encoding step.

HDMI uses transition minimized differential signaling (TMDS) to move information from one place to another. TMDS is a way of encoding the signal to protect it from degrading as it travels down the length of the cable. Here's what happens:

• The sending device, such as an HD-DVD, encodes the signal to reduce the number of transitions between one (on) and zero (off). Think of each transition as a sharp drop-off -- as the signal travels, this drop-off can begin to wear away, degrading the signal. The encoding step helps protect signal quality by reducing the number of chances for the signal to degrade.
• One of the cables in the twisted pair carries the signal itself. The other carries an inverse copy of the signal.
• The receiving device, such as an HDTV, decodes the signal. It measures the differential, or the difference between the signal and its inverse. It uses this information to compensate for any loss of signal along the way.

HDMI encodes, carries and decodes digital signals to high-definition displays, like HDTVs.

HDMI also has the ability to protect data from piracy. It uses high-bandwidth digital copy protection (HDCP) to accomplish this. HDCP is an authentication protocol. Basically, each home-theater device has identification data and encryption data stored on its extended display identification data (EDID) chip. The source device, such as a Blu-ray player, checks the authentication key of the receiving device, such as an HDTV. If both keys check out, the sending device moves on to the next step. It generates a new key and shares it with the receiving device. In other words, it creates a shared secret. Ideally, this whole process, known as a handshake, takes place almost instantaneously.

HDMI Handshake Problems One common problem people experience with HDMI is handshake failure. Sometimes, this is because the HDTV is an older, DVI-based model without HDCP support. But in other cases, there's an easy fix -- unplug your components and power cycle your system. This may reset the authentication cycle and restore your connection.

The source device encodes its information using the key it generated it. The receiving device decodes it using the same information. If an unauthorized device tries to intercept the data, the source device stops transmitting. It also makes sure that the key hasn't changed and that the system is still secure every few minutes. All HDMI-compatible devices are required to support HDCP, but the companies that manufacture and distribute high-definition content aren't required to enable it. In the United States, this content-protection ability is mandated by the Federal Communications Commission (FCC).

Next, we'll take a look at the HDMI connector and cable and explore how they carry high-definition signals.

HDMI Connections

There are lots of methods you can use to connect home-theater components. For example:

• Component video carries analog video signals separated into two channels for color and a third for luminance. Component video cables use RCA connectors.
• S-video transmits analog signals using one cable and a four-pin connector.
• DVI, or digital visual interface, is a 29-pin connection commonly used with computer monitors. Unlike composite video and s-video, it carries digital signals.

Many HDTV early adopters rely on DVI, since it hit the market before HDMI did. Since DVI and HDMI both use the TMDS protocol, they're compatible. All you need to connect an HDMI cable to a DVI port is a passive adapter.

With a simple adapter, you can plug an HDMI cable into a DVI slot.

The DVI and HDMI connectors have some other similarities. Both use a grid of pins to transmit signals from the cable to the device. While DVI has a 29-pin connector, HDMI's type A connector has 19 pins. A DVI connector also uses a pair of built-in screws to anchor it to the device. HDMI plugs don't have this extra support, and some users have expressed concern that this puts unnecessary strain on the device's circuitry. There's also a miniature version of the HDMI connector for use on smaller devices like digital camcorders as well as a 29-pin type B connector, although most consumer devices use type A.

From the HDMI connector's pins, signals travel through twisted pairs of copper cable. Three audio and video channels travel through two pins each, for a total of six pins. The TMDS clock, which allows devices to synchronize the incoming data, travels through one pair of pins. Each of these four total pairs has a shield -- another wire that protects it from interference from its neighbors. The TMDS channels, the clock and the shields make up the bulk of the cable pairs inside the HDMI cable.

The other signals that travel through the HDMI cable need only one pin. One such channel is the consumer electronics channel (CEC). If your devices support it, this channel allows them to send instructions to one another. For example, an HD-DVD player could automatically turn on a home-theater receiver and an HDTV when it started playing a disk. The hot plug detect channel, which uses one pin, senses when you plug in or unplug a device, re-initializing the HDMI link if necessary. The one-pin display data channel (DDC) carries device information and the HDCP encryption information discussed in the previous section. Other channels carry encryption data and electricity to power communication between devices.

HDMI Certification In order to carry the HDMI logo, devices and cables have to pass compliance testing. Manufacturers, known as HDMI adopters, must submit a sample of their product for tests before starting mass production.

The cables themselves come in two categories. Category 1 has a speed of 74.25 MHz. Category 2 has a speeded of 340 MHz. Most consumer cables are the faster category 2 variety.

In addition to the connector and cable, the HDMI standard applies to how TV sets can synchronize sound with video and display color. These capabilities have changed significantly over several revisions to the standard, which we'll compare in the next section.

wHat is 1080p (full HD)

1080p is the shorthand name for a category of HDTV video modes. The number 1080 represents 1,080 lines of vertical resolution (1,080 horizontal scan lines), while the letter p stands for progressive scan (meaning the image is not interlaced). 1080p can be referred to as full HD or full high definition although 1080i is also "Full HD" (1920x1080 pixels). The term usually assumes a widescreen aspect ratio of 16:9, implying a horizontal resolution of 1920 pixels. This creates a frame resolution of 1920×1080, or 2,073,600 pixels in total. The frame rate in hertz can be either implied by the context or specified after the letter p (or i), such as 1080p30, meaning 30 Hz.

A 1080p picture, with a resolution similar to that of 2K digital cinema technology, is sometimes referred to in marketing materials as "Complete High-Definition". However, 4K digital cinema technology is commercially available, and ultra-high definition video is in the research phase.

The meaning of 1080p as a display resolution is not correct because in fact 1920x1200/1920x1080 displays may or may not be able to display 1080p video. Use of 1080p and the closely related 1080i labels in consumer products may refer to a range of capabilities. For example, video equipment that up scales to 1080p takes lower resolution material and reformats it for a higher resolution display. The image that results is different from the display of original 1080p source material on a native 1080p capable-display. Similarly, equipment capable of displaying both 720p and 1080i may in fact not have the capability to display 1080p or 1080i material at full resolution. It is common for this material to be down scaled to the native capability of the equipment. The term "native 1080p-capable" is sometimes used to refer to equipment capable of rendering 1080p fully.

1080p24:

But it doesn't end there. 1080p itself can be broken into two distinct formats. What we normally refer to as "1080p" could also be called 1080p60, and now there is also a variation called 1080p24. The final digits refer to the frame rate at which each runs. Several Blu-ray players offer 1080p24 video output over HDMI in addition to the usual 1080p60, and just recently Toshiba added 1080p24 output to their HD-XA2 and HD-A20 HD DVD player models as well. So what's the big deal? How does each work and is there really a visible difference between them? To explain, we must first understand the way that movies are adapted to video.

Theatrical motion pictures are usually shot on 35mm film, running at a speed of 24 frames per second (even those movies shot on other media use the 24 fps speed for theatrical compatibility). When projected back at the same rate, the image maintains a natural-looking representation of motion. People on screen walk and talk normally, without any 'Keystone Cops'-style sped up movement, unless done intentionally for effect. In contrast to this, NTSC video runs at a rate of 60 interlaced fields per second (59.94 to be more precise). For the sake of consistency, North American HDTVs continue to use a 60 Hz rate, though models with progressive scan will display 60 whole frames each second rather than interlaced fields. Television broadcasts are still transmitted at 60 Hz, and High Definition disc players of both formats also primarily output their video at that rate, either in fields or frames depending on which resolution output you choose.

Similar to what happens with film projection, video material specifically shot at 60 Hz (the evening news, for example) and then played back on TV at that same rate will look perfectly natural. The key to fluid motion is that the original capture speed must match the display playback speed. Unfortunately, we run into an obvious conflict when transferring 24 fps movies to 60 Hz video. If you were to simply speed up the picture to match the faster frame rate, you'd wind up with very distracting visual and audible changes to the movie, everything moving too fast and the soundtrack raised in pitch as it is also sped up to match. Clearly, that's not an acceptable solution.

To get around this, a process called "3:2 pulldown" was developed, in which the original 24 fps film frames are multiplied into an alternating pattern of 3s and 2s. The first frame is displayed 3 times, the second frame twice, the third frame 3 times, and so forth in series. This repetitive sequence effectively stretches 4 film frames into 10 video frames, allowing the original 24 fps content to play at the faster 60 Hz rate without appearing sped up. For a more detailed technical explanation of the process with visual illustrations, I recommend reading through articles at Secrets of Home Theater and High Fidelity and Wikipedia.

The downside to 3:2 pulldown is that it can leave the picture with an artifact called judder, where the repeated frames cause what should be smooth fluid motion to look slightly jerky. The problem is usually extremely subtle, and most viewers raised watching 60 Hz television have probably never noticed it. In fact, even when deliberately looking for it, judder can be difficult to see except during slow, steady camera movements. The opening credits sequence to the movie 'Sahara' provides a good example as the camera slowly tracks from object to object in the room. Nonetheless, for the most part it hasn't been an issue of much concern to most viewers.

We home theater fans can be nit-picky perfectionists, though. For those who demand nothing short of flawless video performance, what's to be done? The solution is to restore the movie to its original 24 Hz playback speed. In the Standard-Def DVD world, this normally requires an expensive external video processor to employ a function called "reverse telecine" that removes the extraneous frames from the video. Things are a little bit easier on Blu-ray and HD DVD, fortunately. The majority of movies on both High Definition disc formats are natively encoded as 1080p24 video frames. For their standard 60 Hz video output, the disc players themselves employ 3:2 pulldown by multiplying some frames 3 times and others twice. However, certain players also offer a raw 1080p24 output setting that bypasses the 3:2 pulldown step and transmits the video over HDMI at its 24 Hz encoding rate (technically 23.97, but the difference is indistinguishable from the original 24 fps film speed).

In order to get this to work, the signal must be transmitted to a compatible television that can properly sync with the 24 Hz frame rate, or convert it to an even multiple such as 48 Hz, 72 Hz, 96 Hz, or 120 Hz. Most HDTVs will not accept a 1080p24 input signal at all, and even among those that will, some simply convert the signal back to 60 Hz by applying their own 3:2 pulldown and re-introducing the judder. In other words, even if you can get the 1080p24 output of the disc player to work, your TV may still not be able to benefit from any improvement it promises.

In a best case scenario, when a player that offers 1080p24 output transmits the signal over HDMI to an HDTV that can accept and sync with the signal, the improvement over standard 1080p60 will still be very subtle. You may have to strain to find it, or do comparison tests of certain movie scenes at both frame rates. If you don't have equipment that will support 1080p24 video and you've gone this far in your life without ever noticing 3:2 pulldown judder, this may one of those things better not to worry too much about.

1080p24 output is only beneficial to content originally photographed at 24 frames per second. Any material shot at a different frame rate, such as most video bonus features found on HD DVDs and Blu-rays, will look very poor if converted to 24 Hz, so be prepared to change the player back to one of the standard 60 Hz resolutions if the player doesn't offer a "Native" mode that will do that for you automatically.

It should also be noted that the 24 fps photographic speed is a fairly slow capture rate that has its own inherent jerkiness in many situations that will not go away with 1080p24 output. The best you can do is eliminate the specific 3:2 pulldown judder, restoring the picture back to whatever level of jerkiness is present in the source. That said, 1080p24 should provide generally smoother motion that sensitive viewers will find a welcome benefit, and it brings a video image one step closer to recreating the original photography.

Stunnung stereo performer...........

"Harman Kardon's top-of-the-line AVR65 surround receiver is a shining example of HK's long-standing tradition of mating useful, creative features with outstanding sonic quality..."

"The AVR65 delivers knock-out dynamics, delicate imaging, deep bass, and clear, extended high frequencies, showing sincere consideration for stereo devotees and home-theater enthusiasts alike..."

specs:
65 Watt - 8 Ohm - 20 - 20000 Hz - THD 0.07% - 5 channel(s) 325 wat receiver



here is part of a review on it
You won't mistake a H/K AV receiver for anything else where frontal looks are concerned, and the AVR65 is every bit a H/K--clean, straight lines give the design a distinctly angular, almost utilitarian, solidity. Still, every function you need to run the unit is on the neatly aligned fascia. Build quality is pretty tight, though I did manage to yank out one of the RCA input jacks' outer screen with a Wireworld 'connect.

In many ways, the AVR65 is a mirror of the DD-equipped AVR45; most of the functions and features are identical, save the power rating and processing options. The AVR65 has a power output rating of 100 watts per channel into eight ohms, 10 more than the AVR45. In the case of the second point, Dolby Digital and Pro-Logic is joined by DTS operation (incidentally, the first in a H/K AVR), so it's all quite up to current specs.

In terms of inputs and outputs, there should be enough to handle most users' demands--four video (one's on the front panel) and two audio inputs, a coaxial and an optical digital input, along with a full set of pre-outs and a discrete 6-channel input (a welcome addition) make up the list. As for video switching, S-Video is comprehensively thrown in for the ride, with three inputs and two outputs (monitor and record) the magic number.

All good and fine, though I'd have liked to have seen more digital inputs on the AVR65. A couple more, preferably of the coax variety, wouldn't have gone amiss; these days, it's not uncommon to have more than one main source, and in my case, it proved a tough call on deciding which of the source machines--DVD, CD and LD (not quite done in completely, yes?)--got the coax feed. Speaking of which, a built-in AC-3RF demodulator would also have been nice, and it really doesn't cost that much to have one on, does it, H/K?


Performance

The unit was mainly assessed against the vaunted Sony STR-DA50ES, a unit priced slightly higher than the AVR65 but well within the sub-RM4,000 price bracket level the H/K resides in. Also, coming in from a useful term spent with the AVR45 helped in defining the AVR65's abilities and advancements, if any, in relation to the former.

Now, at the beginning of the review, I mentioned that it'd been a long time since H/K had turned any two-channel stereo tricks really worth hollering about in its products. Well, the AVR65 does warrant a holler or two.

It's not perfect, of course. The sound is still a little congested in the lower midband, while detailed and clean, is a ways away from thoroughbred silkiness, and the slight forwardness in the balance can, through equally bold and dominant loudspeaker partners, be ultimately tiresome in stereo over a long run. Still, there is much to like, very much, really, and the pros of an open, dynamic sound, with a wide stage and above average separation aspects far outweigh the cons.

In surround sound operation, the AVR65 is equally competitive, and kept pace with the class-leading STR-DA50ES nicely, if differing in final scope. In both DD and DTS (more so), the Sony sounded more open in terms of envelopment and separation, but the AVR65's excellent sense of dynamics and sheer muscularity of projection made for a fuller, more dramatic presentation. Both AVRs have their strong points, and while ultimately I'd still hedge my money on the Sony (if HT was my primary concern), it's a pretty close call. Both ultimately size up well for prospective buyers, and how the vote goes will depend on the material that'll primarily feed each. Action genre fans, look no further.

Conclusion

In all, a high-scoring achievement, the AVR65. Its stereo performance surprised me, being of an order much higher than I was expecting, and the closest H/K have come to replicating since the AVR30. Add to that a big, gripping sound in its intended field of battle, home theatre, and it's a nice, tight package on the whole, one worthy of recommendation. Welcome back, H/K.