Back in January, in an article about iPod accessories at CES , I talked about iTunes Tagging , a unique new technology that attempts to solve the decades-old dilemma of hearing a song on the radio but not knowing what it is or where to buy it. The short explanation of iTunes Tagging: when you hear a song you like on HD Radio, you press a button on your radio to "tag" the song; your iPod later transfers tag data to iTunes on your computer, where you can click another button to purchase the song.

If the folks behind HD Radio have their way, iTunes Tagging will eventually find its way into a wide range of products, from home stereos to car-audio systems. But right now, the technology is found only in a limited number of iPod speakers. Polk's US$499 I-Sonic ES2 is the first of those products we've tested.

Familiar territory

In many ways, the I-Sonic ES2 is similar to myriad other "desktop"-sized iPod speaker systems. At 14.3 inches wide, 10 inches deep, and 5 inches high at its longest dimensions, it's large enough to offer good sound quality but small enough to fit on a desk, nightstand, or countertop. That said, the I-Sonic's angled front, up-swooping top, and curved sides give the system a somewhat-unique appearance.

On the top is an iPod dock cradle, using Apple's Universal design, that charges your iPod while grabbing audio and video via the iPod's dock-connector port. (Polk includes dock inserts numbers 3, 4, 5, 6, 7, and 12, accommodating iPods from the original iPod mini to the final fourth-generation models, as well as the iPhone. Other dockable iPods include their own adapters, although those are white, whereas Polk's adapters are black. Also, as noted below, iTunes Tagging doesn't work with all iPods.) A nice feature is a flip-down door that hides the dock cradle, and keeps out dust, when an iPod isn't docked. Next to the dock, and also under this door, is a headphone jack for private listening.

The top of the I-Sonic ES2 also hosts an array of controls for controlling volume, the system's radio tuner, the built-in alarm clock, iPod playback, and audio source. The buttons are clearly labeled and easy to use, although iPod-playback control is oddly limited to skipping/scanning tracks; you must use the iPod's own Click Wheel or the I-Sonic's wireless remote for pausing and resuming playback. All other iPod control requires the iPod's Click Wheel, which can be difficult with the iPod nano thanks to the depth of the I-Sonic's cradle. (Note that whenever you switch to the iPod as the audio source, including turning on the I-Sonic if the iPod was the last-used source, the I-Sonic automatically resumes playback; your iPod is paused when you turn off the I-Sonic or switch to a different audio source.) There's also a Settings button that lets you tweak the I-Sonic's bass and treble levels, adjust the built-in screen's backlight and contrast levels, set Sleep mode, and choose the gain level of the auxiliary-input connection (noted below).

On the front of the I-Sonic, you'll find a 2.5-inch by 1.25-inch screen that displays information such as the time, the current audio source, and, when in radio mode, the current radio station and station signal strength. In addition, if a station includes the information in the signal or if you're listening to a newer iPod, the screen will display artist and song names. (This feature doesn't work with iPod mini and fourth-generation iPods, including the iPod photo.) For the most part the screen is clearly readable; however, with quickly-changing text--for example, when scanning radio stations or when a station broadcasts scrolling text--you'll see some ghosting, and the text is too small to read from across a bedroom or office. I also found that some special characters that appear correctly on the iPod's screen do not appear correctly on the I-Sonic's screen; for example o becomes A3.

The front of the unit also hosts two (left and right) 2-inch treble/midrange drivers hidden behind removable gray-fabric grilles. But unlike many other iPod speaker systems, the I-Sonic also has two similar speaker drivers on the back of the unit, which means you don't have to be sitting directly in front of the system to enjoy its audio; those behind the I-Sonic can enjoy roughly the same sound quality as those sitting in front of it. (Polk calls this design I-Sonic, which is where the system gets its name. The company also sells another I-Sonic system without iPod compatibility.)

Finally, the back of the I-Sonic ES2 hosts connections for AM and FM antennas (an AM antenna and two FM antennas--one single-wire and one dipole--are included); left and right RCA inputs for connecting an auxiliary audio source; left and right variable-level RCA output for connecting the system to a larger audio system; composite- and S-video outputs; and a USB "service port" (presumably for potential software upgrades). The I-Sonic ES2's video outputs--for viewing your iPod's video and photos on a TV--work with all video-capable iPods, including the iPod classic, third-generation iPod nano, iPod touch, and iPhone. The use of RCA connectors for audio input and output makes the I-Sonic feel more like a good stereo component than a desktop radio.

The included wireless, infrared remote control offers a nice set of options for controlling the I-Sonic, including basic power, volume and iPod-playback buttons; Tune, Seek, and Preset buttons for the radio; Sleep and Alarm controls; direct access to each audio source ( FM, AM , auxiliary, and iPod); and buttons to adjust the display and engage the iTunes Tagging feature (covered below). The remote uses a "bubble" button design--slightly-raised buttons built into the surface of the remote--which I generally don't like, but the buttons have a much better tactile response than most of this type. The remote's range is very good, even off to either side, although there's a bit of a delay between pushing a button on the remote and the I-Sonic responding.

Finally, those looking for a "complete" home-entertainment system will welcome an upcoming add-on DVD player that will mount directly underneath the I-Sonic ES2.

Listen in HD

As with a number of desktop iPod speaker systems, the I-Sonic ES2 includes a clock radio with a single alarm and a sleep function. The clock, alarm, and sleep functions are easy to set, and you can choose to wake up to an alarm tone or the radio (but not your iPod). Sleep mode and the alarm can be set using either the wireless remote or the buttons on the I-Sonic itself. When the system is turned off, the time display fills the screen and is readable from across the room; as mentioned previously, you can also adjust the screen's brightness and contrast. A nice touch is that the large Snooze/Mute button, just in front of the iPod dock, has three raised dimples on it, making it easier to locate by touch when you're waking groggily from sleep.

It's the I-Sonic ES2's radio that really makes it stand out from the crowd. In addition to standard AM/FM tuning, the I-Sonic also supports HD Radio . For those who've never used HD Radio, it's essentially a free, higher-quality, digital alternative to standard radio. As long as your favorite station broadcasts in HD, you can listen to that HD version for free with any HD tuner. (Although HD Radio is available for both the AM and FM bands, most stations that have upgraded to HD broadcasts are found on the FM dial.) HD Radio uses High Efficiency AAC (HE-AAC) to compress audio, and currently lets AM stations provide sound quality roughly comparable to traditional FM stereo, with HD Radio FM offering noticeably better sound. (HD Radio proponents claim FM is "CD-quality," but it's not.)

HD Radio also offers several other benefits. A major one is that, because the signal is digital, there's no multi-path interference or static--for the most part, stations either tune in well or they don't tune at all. (Most current HD radios automatically fall back to standard AM or FM if the HD version can't be received reliably.) So you generally get a clear signal. Another feature is enhanced text information. Similar to the RDS feature available to traditional analog stations, HD Radio stations can include textual data in their signals. For many stations, this is essentially artist names and song titles, but it can also include information such as weather or traffic alerts. The I-Sonic ES2 displays this text on its screen.

Finally, another benefit of HD Radio--perhaps the most compelling one for many people--is additional content. Specifically, each station can have multiple "channels," each with different content. For example, near my home here in the San Francisco/San Jose area, the FM radio station KFOG broadcasts on 97.7. The HD version of KFOG has two HD channels: 97.7-1, which mirrors the analog version, and 97.7-2, which continually broadcasts episodes of KFOG's well known "10@10" radio program. (The downside to offering multiple channels is that the audio quality of each channel is reduced as the broadcaster splits its assigned bandwidth into several smaller streams.)

The I-Sonic ES2's radio tuner works well overall, although it does have a few annoying issues. On the positive side, when you tune to an FM frequency, the radio automatically checks to see if an HD alternative is available; if so, the radio automatically switches to the HD version and an HD icon appears on the screen. If multiple channels are available for that HD station, you then tune to them using the standard Tune and Seek controls; for example, if you're listening to 97.7-1, pressing the Tune Up or Seek Up button will take you to 97.7-2. FM reception--analog and digital--was very good for my area, outperforming a number of other radios I've tested, and the I-Sonic was easily able to lock on to the HD version of most FM stations in my area that offer such a broadcast.

On the AM side, analog AM reception was typical of radios I've tested, which is to say not very good; static and interference made few AM stations listenable. On the other hand, reception for AM HD Radio stations--which, unfortunately, are few and far between in my area--was eye-opening. The initial tuning--to the analog version--presented a scratchy, staticky signal, but a few seconds later the I-Sonic ES2 locked on to the HD version, producing a clear, even enjoyable, signal.

(Although I'm not sure why you'd want to, I couldn't find a way to manually revert from the HD version of a station to the analog version.)

On the downside, sometimes after releasing the Up or Down button, the tuner seemed to have momentum, speeding right past the desired frequency and not stopping for some time. (I think what was actually happening is that the screen was often slow to "catch up" to the frequencies being scanned. For example, when scanning from 97.7 to 99.7, I'd hear the latter station while the display was displaying 98.5; it would take another second before the display reflected the actual station.) Obviously, this can make scan tuning frustrating. Tuning to an HD Radio station's alternate channels can also be challenging, as you have to first tune to the main station and wait for the I-Sonic ES2 to switch to the HD stream; you can then use the Tune Up button to switch to the -2 or -3 alternate. Finally, one other minor inconvenience is that when you switch to the radio, it can take a few seconds before the radio locks on to the previous station.

The I-Sonic ES2 can save 18 FM and 6 AM presets; alternate HD channels, such as 97.7-2, can be saved as presets.

iTunes Tagging

The I-Sonic ES2 is the first iPod audio system to include iTunes Tagging, a feature that works closely with the data provided by HD-Radio broadcasts. As I noted above, iTunes Tagging is designed to let you easily purchase, through the iTunes Store, songs you hear on the radio. When the feature works, it's both fun and convenient; however, it does have several limitations.

The best-case-scenario, at least with the I-Sonic ES2, goes like this: When you hear a song you like on an HD Radio station, you simply press the large Tag button on the front of the I-Sonic, or the small Tag button on the wireless remote, before the song is over. This saves information about the song--its tag--to the I-Sonic's memory ("Store Tag Data..." appears on the I-Sonic's screen to indicate that the tagging was successful). If your iPod is currently docked in the I-Sonic, that tag is immediately transfered to the iPod; if your iPod is not currently docked, the I-Sonic stores up your tags and syncs them en masse the next time you place your iPod in the dock cradle. (You can store up to 50 tags in the I-Sonic, and these tags are preserved in the I-Sonic even if you unplug the system; once you transfer tags to an iPod, those tags are erased from the I-Sonic.)

The next time you sync your iPod with iTunes, tags are transferred to a Tagged playlist that appears in the Store area of iTunes' sidebar. Click on this playlist, and you'll see a list of all the songs you tagged, with information such as track and album name, artist, a comment--usually the name of the station playing the track when you tagged it--and a Buy or View button. Click on the Buy Song button to buy the track immediately, or click on View to view the track on the Store, usually in the context of the song's album. (I wasn't able to determine why some tracks have a Buy Song button but others have a View button.) You can also "gift" your Tagged playlist to someone, or publish it as an iMix, by clicking the right-facing arrow next to the Tagged playlist in the iTunes sidebar.

Unfortunately, things aren't always so seamless. As you can see in the screenshot above, tags are seldom complete. Some tracks have no information at all, while others include only the name of the radio station; clicking View for these tracks takes you to the iTunes Store's Power Search screen. And in this sampling of 13 tags, only one track included the album name. I'm assuming incomplete tags are a result of the source radio stations not including complete information. Whatever the case may be, the upshot is that iTunes Tagging currently doesn't work as reliably as you might expect.

Another issue is that when artist and song title information are present but no album info, iTunes apparently tries to find the "best" match for the track. This means that if several versions of a song are available, on different albums, the version you get when you click on the Buy Song or View button may not be exactly the same as the version you heard on the radio. Even if the versions are the same, if you're interested in buying the entire album, the View button may take you, for example, to a greatest-hits album rather than the original source album. And in some cases--for example, the Radiohead track in the list above--you're taken to a list of albums or EPs by the artist.

There are also a few limitations to iTunes Tagging in general. It obviously works with only HD Radio stations, so if your favorite station doesn't have an HD Radio version, you're out of luck. It also requires an iPod classic or third-generation iPod nano; older iPods, as well as the iPod touch and iPhone, won't transfer tags to iTunes. (iTunes itself must be version 7.4 or later.)

Finally, in terms of the I-Sonic ES2's hardware, I found the large Tag button on the front of the system difficult to press. In fact, if you press the bottom half of the button, nothing happens at all; you have to press the top half firmly. I much preferred using the easy-to-press Tag button on the wireless remote.

One other comment on the iTunes Tagging feature: a few readers of my original coverage of iTunes Tagging, back in January, expressed concerns that there were too many steps involved in the process: you have to tag a song; then, if your iPod isn't already connected, dock it with the radio; then sync your iPod with your computer. As it turns out, this sequence of events tends to take care of itself, so to speak. I tend to sync my iPod with iTunes every few days, and I found that I put my iPod in the I-Sonic regularly enough that I rarely had to specifically go through the process to transfer tags to iTunes.

I-Sonic's sonics

The I-Sonic offers a level of audio quality I've come to expect from a better desktop system: clear treble, good midrange, and--thanks to a large, internal enclosure and a bass port on the bottom of the system--solid upper-bass, although little lower bass. Stereo separation is typical for a one-piece system, which is to say that there's not much, although thanks to the I-Sonic's four speakers, you do get a sense of "fullness"--more sound in the room--that you don't get with similar systems. On the other hand, the I-Sonic's audio is not quite as good as that of some of our favorite desktop systems, such as JBL's $300 Radial or Logitech's AudioStation . The Radial's treble and midrange are a bit more engaging, while the AudioStation offers noticeably better bass response. (The I-Sonic does offer treble and bass adjustments; however, these controls let you emphasize or attenuate existing frequencies--you can't increase frequencies that are simply out of the I-Sonic's range.)

One area in which the I-Sonic does have the upper hand over most other desktop systems is in directionality--or, as the case may be, a lack of directionality. As I mentioned previously, instead of using a pair of speaker drivers, the I-Sonic features two pairs: one left/right pair in front and another in back. This four-speaker array lets you enjoy the I-Sonic's audio even if you're behind the system--a capability few, if any, other desktop audio systems offer. In addition, the orientation of the rear drivers is reversed so that the right channel is on the right-hand side when you're facing the back of the system. This means you get accurate left/right channels even when listening from the rear. (It also means you can hear both channels--though reversed and, given that the drivers aren't facing you directly, with lower quality--if listening from either side.)

In my testing, the rear speakers didn't sound quite as good as the front set, but listening from the rear was still better than with any other iPod speaker system I've heard. That said, given the cables and connectors on the back panel, I wonder how many people will place the I-Sonic ES2 in a position where people will be in a position to listen from the rear.

A couple other audio-related features are worth noting. First, Polk's Dynamic Loudness Contour automatically increases bass and treble levels at low volumes to account for the human ear's reduced sensitivity to higher and lower frequencies . This feature works well, as even at the lowest volumes, the I-Sonic sounded good. Second, Polk includes a feature called Dynamic Compression that reduces distortion at loud volumes. Even with the volume cranked up on bass-heavy music, I didn't hear any distortion, although the audio quality wasn't as good as at lower volumes.

Macworld's buying advice

At nearly $500, the I-Sonic ES2 is among the most expensive desktop audio systems for the iPod, and its features--which emphasize HD Radio reception and iTunes Tagging--place it in the company of premium table radios, such as those from Bose, Cambridge SoundWorks, and the like. If you aren't a big radio listener or your favorite stations don't have HD Radio versions--in other words, if you won't take advantage of the unique iTunes Tagging feature--you can get similar audio quality for considerably less money. On the other hand, if you're a fan of radio, the I-Sonic ES2 sounds better and has many more features than Bose's popular clock-radio-only $349 Wave Radio . As someone who enjoys the radio now and then, I was impressed with the quality and offerings of HD Radio, and I found myself using the I-Sonic's iTunes Tagging feature frequently. However, Tagging depends on good information from radio stations as well as reliable transfer of that information from the station to the radio, then to the iPod, and, finally, to iTunes; based on my testing, that chain isn't yet completely reliable. When iTunes Tagging worked, it worked well, but those times just made me want it to work all the time.