Apple didn't do much new when it introduced the fourth generation of the iPod, but it didn't need to. No one has beaten the company at the portable-audio-player game yet, but with 75 percent market share, the only way to go is down. The fourth-generation iPod performs pretty much the same as the third-generation player, with some detail improvements. But since we last looked at the player, we've tweaked our audio performance evaluation measures. As a result, we've identified some minor audio issues with the iPod's equalizer (EQ) presets. The iPod, however, is not alone in this, as we also noticed similar problems in other large hard drive players, such as the Archos Gmini XS200, Dell DJ 30, and Toshiba gigabeat MEG-F60.

Like the Archos Gmini XS200 and Samsung YH-925, the iPod distorts, sometimes heavily, when you use the EQ settings. Harmonic distortion is minimal with no EQ, but at higher volume levels most of the EQ settings showed audible distortion. When we couldn't hear it, we could see it plainly on our audio spectrum analyzer. Bass response is about 5 dB down at 40 Hz, the practical lower limit for most music.

The integrated click wheel and buttons that work so well on the iPod mini are now on the full-size iPods, too. It's an improvement over separate buttons, and it keeps the iPod at the forefront of user-friendliness. We also wonder why hardly anyone else can do a screen this readable. Only the Creative Zen Micro comes close among monochrome screens. The big iPods now recharge from USB, and battery life is up to around 12 hours.

Readers have asked whether there is less distortion when using the line-out jack on the dock. When we measured the amount of distortion on headphones at listening volumes, we found the same amount at both jacks. But feeding into a stereo system or external headphone amplifier requires much less output power and doesn't require EQ in the player, so the music will be clean. With Apple Lossless compression, the iPod is just as capable as your CD player is of driving a high-end audio system. If you select EQ presets in iTunes (which doesn't have the distortion problem), however, your iPod will switch to your chosen EQ on a per-song basis when you download to the player.

Another reason to own an iPod is the tremendous number of aftermarket products and accessories. There's certainly much more available than with any other large hard drive player out there. You can extend its capabilities with hardware and software to perform PDA functions, gaming, recording, wireless transmission, and more. It's a platform, it's a social phenomenon, and it's a robust device with millions of satisfied users, despite our carping about distortion. The human factors are still the best, and there's some excellent usability engineering in this fourth-generation player.

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