FM transmitters aren't the perfect way to listen to an iPod in a car, but sometimes they're the best option. Cassette adapters give better and more reliable sound, but work only when the car actually has a cassette deck (an option that's hard to find these days on new cars). A direct auxiliary input gives even better sound, but such inputs are even more rare than cassette decks. A custom-designed iPod interface (such as found in some models of BMW cars) is coolest of all, but expensive, and no good if you drive multiple vehicles, as I do at work. An FM transmitter works with any FM radio, and is small and easily carried between cars. So, while an FM transmitter may not provide the best-sounding iPod audio, it is the most universal.
The last time I reviewed FM transmitters for TidBITS, my overwhelming favorite was the Griffin iTrip (see "Taking an iTrip: Three FM Transmitters" in TidBITS-681). Its performance wasn't anything to cheer, but it was about as good as the others I looked at on any given frequency - and it worked on more frequencies than one competitor and with greater precision and reliability than the other, despite its clever but Rube Goldbergian tuning method. However, the iTrip's biggest assets are two design features: it draws power from the iPod, eliminating the need for batteries; and the iTrip itself is so small and light that it can be carried as a clip-on to the iPod almost as easily as carrying the iPod by itself. Several FM transmitters have come on the market since my original review, with varying combinations of features, but none of them could match the iTrip's design.
Of course, that must have changed, or I wouldn't be writing this review. At January's Macworld Expo, XtremeMac came out with the AirPlay, their own clip-on FM transmitter which draws power from the iPod.
Design -- The AirPlay doesn't fit together with the iPod as well as the iTrip does; it's taller, and it doesn't extend across the width of the iPod, leaving me with the uneasy (if probably unjustified) feeling that it's more likely to break off if banged around. An iPod or iPod mini plus the corresponding iTrip looks and feels like one piece; the AirPlay hangs off awkwardly by comparison. However, its design boasts a couple advantages over the iTrip: the same unit fits both the regular iPod and the iPod mini, and it gives you access to the Hold switch.
The AirPlay also has one feature the iTrip can't touch: a built-in display with a digital tuner that's manually controlled. The last feature wasn't enough to tempt me on other transmitters, which, when compared with the iTrip, were often bulky and unwieldy. On a slim, clip-on transmitter like the AirPlay, the manually controlled digital tuner makes all the difference in the world.
The iTrip's digital tuning feature, which operates via special MP3 files on the iPod and displays on the iPod's screen, was a quantum leap over the analog tuner in another transmitter I tested. Instead of trying to turn a dial a fraction of an inch to lock in on a frequency, I could pick and set any specific frequency with relative ease using the iPod's controls. The iTrip manages this, on a device with no moving parts, through a series of encoded sound files, one per frequency; playing the appropriate file through the iTrip sets the frequency.
Unfortunately, while clever, this method has problems. Changing frequencies means interrupting what you're playing to use a tuning file. It also makes hunting for a new frequency somewhat tedious; play a frequency file, return to the previous menu to play a song to test the new frequency, go back to play another frequency file if the previous one didn't work well, etc. For this reason, tuning with the AirPlay is as much a quantum leap over the iTrip as the iTrip was over an analog tuner; the AirPlay and radio can be adjusted together with precision while your song keeps playing.
Performance -- I wrote a fairly extensive description of FM transmitter performance issues in my prior review, and I recommend that you go back and read it, because things haven't particularly changed since then. In a nutshell, transmitter performance is highly variable; the number of local radio stations, layout of nearby buildings, model of car and location of the radio antenna, and even where the iPod is sitting in the car can cause significant shifts in performance.
The AirPlay, alas, is no different. In several weeks of testing, including lots of driving around Kansas City and a couple of longer road trips, the AirPlay performed comparably to the iTrip; at times it seemed to handle some spots a bit better, at other times a bit worse, but at all times the differences were so small that it could easily have been my imagination. In other words, don't start looking at the AirPlay thinking it'll crank out a stronger signal; its advantage over the iTrip lies in doing a better job of finding a usable station, just as the iTrip had the same advantage over the competitors I tested against at the time. (The same fact would be true of other transmitters with a manually operated digital tuner, by the way. The AirPlay's advantage is that it's the first transmitter to combine a manually operated digital tuner with the size and battery-free operation of the iTrip.)
Conclusions -- The iTrip is still the most elegantly packaged FM transmitter; in standard and mini versions, it fits with appropriate iPods as if they were designed together. The AirPlay is a bit clumsy by comparison. (To give a specific example: when charging the iPod through the dock connector, I could rest the iPod and iTrip combination on its "head" while it charged. If I tried that with the iPod and the AirPlay, it would probably fall over.) The AirPlay also lists for $40, $5 more than the iTrip, and the iTrip can frequently be found on sale for another $5 to $10 off. But in the end, the AirPlay fixes the iTrip's one major flaw while retaining most of the iTrip's design advantages. I liked the iTrip a lot and in a way am sorry to see it topped, but until something better comes along, the AirPlay is now my tuning companion of choice.
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