Creative's Xmod is an interesting little product that manages to bring Creative's patented X-Fi sound processor into a portable form factor. It has a few issues most notably that it relies external power when connected to a non-PC source and the required AC power cable is not provided, but other than that it offers brilliant audio quality at an affordable price.

The coolest thing about this device is that it is portable. The whole unit is smaller than a deck of cards and is extremely lightweight. This makes it brilliant as a companion for a laptop without a high-end or dedicated sound card. However this form-factor is also useful if you are on the move a lot, or have multiple PCs and want to enjoy X-Fi quality audio on all of them.

However, it isn't a fully fledged X-Fi Card and doesn't have all the features and settings available on a regular, internal card. What it does offer are two key technologies that have an impact on movies and music, namely CMS-3D and Crystaliser.

CMS-3D is quite funky. It is basically an enhanced surround sound mode, which improves directional and position audio. We found it was reasonably effective at this, creating a more immersive listening experience, with more definition and better placement of individual instruments and sounds. However, some of the audio became stunted, sounding clipped, and a lot of the detail was lost when this feature was activated. We wouldn't recommend this mode for music listening, but for enjoying other media, such as games or movies, it was quite effective.

The real gem of this product, however, is the X-Fi Crystaliser mode. With this switched on, the X-Fi processor theoretically enhances your music up to 24-bit quality, which is above that of a regular CD (CDs are 16-bit). The idea is that this will have a big impact on compressed music such as MP3s, although Creative also claims it will make your CDs sound better than standard CD quality.

It does this by taking certain frequencies at extreme ends of the spectrum and fills in sounds that it calculates are missing. We were a little skeptical at first, concerned it would simply increase the range on certain sounds, but a few seconds of comparative listening quickly turned us into believers. The Crystaliser certainly does a great job. Our MP3s sounded much livelier when it was activated. We noticed deeper bass and more prominent highs. The mid-range remains unchanged for the most part, although it seems a little richer, and detail remains about the same whether the Crystaliser is on or off.

We even tried it with some music CDs, putting Creative's claims to the test, and found similar improvements, though not as dramatic. Music definitely sounds more vibrant and has more energy to it. Our only concern is that with the Crystaliser running, the music does have a slightly manufactured digital sound to it. Most people won't notice it, but it may be enough to put off audiophiles. Overall we were thoroughly impressed with how well the Crystaliser did in our tests and the improvement will be obvious to the vast majority of listeners.

There isn't really much else to the unit. It has three controls; a large silver volume knob and two switches for CMS-3D and Crystaliser respectively. It automatically starts up when connected via the USB and has three small blue LEDs that indicate which features are currently turned on. The design feels a little flimsy for a portable device, but as long as you take care not to be too rough it should survive most journeys.

Our main complaint with the design is its reliance on external power. In addition to the headphone and USB jacks, the Xmod has both line-in and line-out, meaning it could be used as a portable headphone amplifier for iPods and other digital music players. The only issue is it won't run without external power. Where a PC powers it directly through the mini USB port, a line-in or headphone connection offers no power input. If it could be battery powered as well, it would be ideal to carry around with you on the road, but the reliance on a computer means it is severely limited.