Frequency Response (7.30) 
Our first test looks at frequencies, examining how well an MP3 player like the X-Fi plays back all of the tones that make up your music. We do this by playing back a special sound file that contains a range of frequencies, with our testing system listening in. This then produces the graph on the right, which shows the response from the low frequencies (on the left) to the high (on the right). The ideal here is a flat line, which would indicate that the MP3 player plays back all frequencies at equal volume.
The X-Fi did a reasonable job here; although the response is flat for most of its length, it does get rather bumpy towards the end, with some frequencies being slightly exaggerated and others slightly supressed. These are mostly minor bumps and dips, though, and few users are likely to notice them. More of an issue is the very high frequencies, though; the player seems to cut these off a little quicker than we generally like to see, which might lead to some high frequency details getting slightly lost in the mix. But this only happens at very high frequencies, and generally the frequency responsne of the X-Fi is acceptable.
One thing to note here is that we disable the equalizer for this test, as this alters the frequency response to appropriately enhance the sound.
Distortion (2.05)
When your music just doesn't sound right, distortion could be to blame. Distortion refers to differences between the origional sound and what you get; problems such as clipping and compression mean that you don't get the original sound. We test for this using a special sound that simulates music because it number of frequencies being played simultaneously, which is a better indicatior of distortion than a single tone.
We found some issues here; the X-Fi had definite distortion across most of the frequency range. To push them to their maximum performance (or lack thereof), we test media players at their maximum volume, which also tends to maximize the distortion, if it is present. The distortion would probably be significantly less if the volume was set lower, but it's not a good sign when a player has this level of distortion.
Crosstalk (8.19)
There are two sides to your music; the left and right channels that get sent to the left and right headphones. And your music should stay that way; what's playing in the left channel should never end up in the right one. That's what we test here; our testing system looks to see if any of one channel gets into the other, a problem called crosstalk.
The X-Fi did not have any major issues here; we measured the amount of crosstalk at around -75.6 decibels, which means that it will be inaudible to all but the most sensitive of ears.
Output Power (6.85)
Media players have to drive headphones, and that's what we test here; how much energy they can produce to drive a bigger set of headphones. Although every player has the wattage to power the headphones they come with, many players lack the muscle to drive a bigger set of headphones, outputting only a handful of milliwatts. The X-Fi didn't have this issue; driving a reference load of 10 ohms, we measured the peak output of the headphone socket at 27.4 milliwatts, which should be enough to drive all but the biggest, baddest headphones. . However, it should be noted that this might be why the distortion is high; if the amplifier within the player is being pushed too hard to improve the output power, distortion can be the result.
Noise (8.96)
Noise is an inevitable fact of life with media players; the converters that turn the digital data back into analog sound and the amplifiers that boos this to the right levels all add some amount of noise. We didn't find much noise from these in the X-fi, though; we measured the signal to noise ratio at 61.9 decibels. Higher is better in this test - it means that there is a wider difference between the signal (the music) and the noise that the amplifiers and converters create. Although other players have higher signal to noise ratios (the iPod Nano, for instance, had a signal to noise ratio of 92.99), the X-Fi has a higher enough rating here that noise should not be a problem.
Included Headphones (8.27)
Most of the headphones that are included with media players are, to be honest, awful; cheap, grungy and leaky. The headphones that came with the X-FI were a pleasant surprise, though; we found that the in-ear headphones had decent frequency response, low distortion and could handle plenty of volume. They were also resonably good at isolating you from the outside world, blocking a lot of sound and not letting much sound escape. Although audiophiles may still want to invest in a better pair of headphones, the headphones bundled with the X-Fi are pretty darn good.
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