Acoustic Research HDP100 HDMI Powerlink System

If you've paid to have your HDTV installed in any kind of permanent way, you know that the cost of installation can often overtake the cost of the television itself. Part of that installation cost involves wiring: running cables from your gear up to the TV, generally through walls. In addition to the high price of long cables, especially HDMI cables, punching holes in walls and making the installation look clean costs big bucks.

In that light, the $300 price tag of the Acoustic Research HDP100 seems reasonable enough. This system is designed to transmit HDMI signals, which consist of audio and video, from your components to your HDTV without having to punch holes in walls or invest in long, expensive cables. It does so in the same way that Ethernet-over-powerline adapters work: using your existing AC power lines and wall sockets. I've had good experiences with Ethernet powerline adapters so I figured the HDP100 would be a great solution to the cables-through-walls problem.

While it generally worked as advertised, the system didn't wholly deliver on its promise, especially to eagle-eyed viewers who might expect the same performance seen from standard HDMI cables. Yes, longer HDMI cable runs can have their own issues, but in my experience they deliver better performance than the HDP100. For now, however, this is the only system of its kind available--wireless HDMI systems are largely vaporware or proprietary, and few other options for HDMI installation exist--so you might not have a choice. If you're a potential buyer of the system, you should also make sure to purchase it from a vendor with a good return policy in case it doesn't work in your location.

Design
The HDP100 system consists of a pair of identical-looking, glossy-black boxes about half the width of a standard DVD player, measuring 8.5 by 5.3 by 1.6 inches (WHD). One is a transmitter and one a receiver. Each has a trio of blue LEDs on the front panel--to indicate power, a link to the other box, and the presence or absence of data being transmitted--and on the back panel, a port for the included infrared extenders (see below), an on-off switch, an HDMI port, and a thick power cable. The company includes a pair of stands for orienting the boxes vertically, along a single wall mount kit and a short, 3-foot HDMI cable.

To set up the system, you plug the power cable of the transmitter box directly into the wall socket near the component whose signal you want to send to the display (the company recommends a direct connection as opposed to connecting the boxes to surge protectors). Then connect that component's HDMI output to the input jack on the transmitter. Next, plug the receiver box's power cable in next to the television, and connect the receiver's HDMI output to the TV's input. Flip the power switches of both the transmitter and receiver into the "on" position. If the system can make its connection between the boxes, which happens automatically as soon as they're both plugged in, all three lights on the front of both boxes will illuminate.

It's that simple. The system either establishes a connection or not. When it can't establish a connection between the boxes, because of electrical wiring issues, too long of a distance between boxes, or some other factor, the "Link" light blinks on both boxes and the display connected to the receiver flashes the message "Check Network."

Features
The HDP100's feature set is quite simple. Each box only has one HDMI connection, so you can't connect more than one component directly to the transmitter box or pass through a connection. The system will take the HDMI output of an AV receiver or HDMI switch, enabling more than one source to transmit to the display, as long as compatible signals are transmitted. For some reason the system is compatible with only progressive-scan video signals: 1080p, 720p, and 480p. It can't pass high-def 1080i or standard-def 480i signals, so be sure to set your source components to output in progressive-scan over HDMI. The system will also transmit audio, of course, although you need to make sure your TV is capable of decoding the audio from the source component or you won't hear anything.

Acoustic Research designed the system to work not from room to room, as most powerline Ethernet systems do, but rather within the same room, as a way to avoid running wires from components to a (typically wall-mounted) HDTV or perhaps a ceiling-mounted projector. In my tests I was able to make a successful connection using various power outlets around the room where the TV was situated, as well as from one or two rooms away within my apartment. Longer connections were unsuccessful. As with all powerline systems, you may experience better or worse results depending on the state of your electrical wiring. A room-to-room installation is certainly viable, especially with the HDP100's infrared transmitter system, but that's not how the system was designed.

The receiver has an IR window on the front panel, and a port for the included external IR sensor. The transmitter has a matching port for the included IR blaster. You can place the external sensor in a location where it will pick up the infrared signal from a remote control--typically near the TV's own remote sensor--and the blaster in front of the connected HDMI component's own IR sensor. Using this arrangement, the system allows you to control your HDMI component using its remote control, or a universal remote, even when the component and the HDP100 boxes themselves are stashed out of sight or in another room.

One potential design problem is that both boxes are always on. The only power control is the switch on the back of the boxes. I would have liked to see some sort of automatic power-up and power-down option, to save electricity if not extend the product's lifespan. I measured a steady power consumption of about 6.8 watts for each box in standby mode, without transmitting (I was unable to successfully measure consumption while transmitting). That doesn't add up to much, but the boxes nonetheless run pretty hot.

Performance
The system did perform its basic task of transmitting audio and video over the power lines I tried. Unfortunately, in every case I witnessed personally, the video quality wasn't as good as with a real HDMI cable connection. Casual viewers may not notice the difference, but videophiles and others who pay close attention may find that the convenience of the HDP100 isn't worth the picture quality tradeoff. I experienced the problems mentioned below in three different locations with two different HDP100 systems, so while it's possible that the wiring in all three locations, and not the HDP100 itself, was at fault, it seems unlikely.

I first tested the system at my apartment in a best-case scenario: plugging both the transmitter and the receiver into the same socket, to minimize the distance the signal must travel. Most installations will have the two plugged into different outlets in the same room, but I just wanted to see how the device performed at its best. These tests were all done in an apartment where powerline Ethernet adapters worked quite well from room to room. I unplugged them during this test.

First I tried out some test patterns and it soon became clear that something was amiss. The PlayStation 3's typically zippy, smooth progress through its own menu system and through the complex animated menus of Digital Video Essentials: HD Basics was comparatively clunky and jerky, and the text didn't look as crisp on my 1080p TV as usual. I confirmed that the connection was in fact truncating the PS3's 1080p output resolution; according to test patterns it looked like about half the normal 1080 lines of vertical resolution were visible. I switched over to 720p and results were better; there was no apparent loss of resolution.

I could forgive the loss in resolution at 1080p since extra resolution is difficult to discern anyway above a certain point, but I can't forgive the choppiness I experienced in moving video. One demonstration sequence from DVE includes some very high-bit-rate animations (above 40Mbps in parts, according to the PS3's display) that choked up the connection. The video would pause briefly, chug forward, and catch again before moving on. Most large-scale movement, such as clouds moving across the sky in time-lapse, again had that characteristic if somewhat subtle chugging, hitching motion, as if frames were being dropped. Pans and camera movement were also susceptible.

I checked out Spider-Man 3 on Blu-ray and experienced the same issues. In the opening sequence, with Spidey swinging above the buildings, the subtle choppiness returned, and when the camera found Parker looking at the billboard, the moving crowd behind him seemed move with that jerky motion. The same thing happened throughout the movie, from the pan over the newsstand to the movement of Parker on his scooter and so on, in just about every scene. Switching to 720p didn't help.

As a picky videophile I would certainly qualify the jerky motion as unwatchable, although some viewers might not mind it as much, especially in scenes with little movement. In fact, I tested this theory by allowing one unsuspecting viewer (my wife) to watch an entire movie via the system, and she didn't notice the choppiness at all.

I attempted other outlets around the house and the results were much the same. On one in the same room I couldn't get a connection at all, and on the other two in the room I experienced the same kind of performance described above. On the plus side, I was able to get the same performance outside the room, too. I tried two other plugs, one in the living room about 20 feet away, and another in the kitchen about 30 feet away.

After a conversation with Acoustic Research, their engineers suggested my home's wiring must be the problem. I sent the system home to the apartments of two other CNET staffers and, sure enough, both reported no problems. But when I connected the system again at the CNET office--granted, not the best test since power supplies at offices can be worse transmitters of signals--I saw the same choppiness and truncated 1080p resolution. Both staffers said that what they saw at home was better than what we all saw at the office, although one admitted that he might not have noticed the choppiness as much since he used a smaller TV.

Flummoxed, I took the system to my in-laws' house over Thanksgiving weekend to give it a try there. Making a similar connection I noticed similar results. The choppiness in Spider-Man was there, along with more obvious false contouring, as if the system was truncating bandwidth as well as dropping frames. Once I pointed out the issues to my father-in-law, he saw them easily enough, although at first he didn't notice.

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