|The Sirius and XM vehicles experienced only one brief signal dropout while going through downtown Denver.|
Throughout the test, we made sure that we were comparing apples to apples. All critical listening to music channels used original broadcasts only. For example, XM's Channel 21 carries KISS, a terrestrial station uplinked from Los Angeles. Since there's no way to ensure that its signal isn't being degraded before it gets to the XM satellites - perhaps because a succession of codecs has been employed - we ruled it and any other "secondhand" stations ineligible for our sound-quality evaluation.
The bottom line: Sirius's sound quality was inferior to XM's - to a significant degree, we thought. But perhaps we set a high bar: one of us teaches the engineers who design audio systems; the other is a recording engineer who spends 8 hours a day critically listening to audio to ensure that the sound quality is the best it can be. Your ears might be more tolerant.
Why didn't Sirius sound as good as XM? There are a number of possibilities. Both systems use digital transmissions, and both limit audio bandwidth (particularly the highest frequencies) and use data-reduction codecs to provide as many channels as they do. But XM uses a version of AAC (Advanced Audio Coding) while Sirius uses sPAC (Satellite Perceptual Audio Coding). Differences between these codecs - such as how they compensate for the way we perceive sound and how they distribute the available bits between the channels - can make a big sonic difference. Compared with encoding, the receiver's chore of decoding the bits back into music is relatively simple, and even doing it badly can't cause the kind of degradation we heard. So the sonic problems weren't the fault of Kenwood's Sirius receiver.
Both XM and Sirius blessed the plan for our comparison before we headed for Denver, and there were no indications from either camp that any work was being done on the systems that would have a noticeable impact on our results. But the differences in sound quality were so apparent that technical editor David Ranada, with the cooperation of both Sirius and XM, set up another comparison in the S&V offices in New York City to make sure that what we'd heard could be attributed to the satellite signals and not the car gear or something else. His listening, over a number of days on a pair of high-end home speakers, confirmed our impressions. Sirius has since told us that it extensively tweaked its system between our trip to Denver and when David did his listening, and that it plans to continue tweaking the sound right up to the July 1 national rollout.
Can You Live Without Satellite Radio?
After our two-day drive, we returned to Denver with some solid conclusions. Both XM and Sirius provide a vast array of programs and awesome content. While there are specific programming offerings that might sway you, both provide plenty of great listening opportunities. No one is eager to pay yet another monthly fee in addition to all their other bills, but the subscription charges are reasonable considering the terrific music selection each system offers. XM is cheaper than Sirius, but it also throws in more commercials. In terms of both cost and content, for our tastes, they were tied.
The robustness of both systems met our expectations, but Sirius provided slightly more reliable reception in this particular test. However, the sound quality is even more important, especially to readers of this magazine. When you're traveling down the highway, windows down and singing at the top of your lungs, you might not notice the problems we described. But when you slow down, and the engine and road noise die away, sound quality will become an issue. At this stage of the game, XM sounds better than Sirius.
Despite whatever qualms we might have had, it's irrefutable that satellite radio is fantastic. Ten minutes after returning our borrowed vehicles, we went into satellite withdrawal. We really missed having all those channels. Of course, you could wait a few years for second-generation radios that'll receive both services and stick with AM and FM in the meantime . . . .