Unlike the cheaper Xonar DS, the Xonar DX card uses an Asus AV100 audio processor. It's another rebadged C-Media CMI-8788 OxygenHD, so there's no practical difference between the quality of this audio processor and the AV200, despite Asus's claims that the latter are cherry-picked to ensure higher quality. The audio processor doesn't have native PCI-E support, so you'll also notice a PLX PEX 8112 PCI-E bridge chip on the card.
Digital-to-analogue conversion for the front outputs is handled by a Cirrus Logic CS4398, while a Cirrus Logic CS4362A deals with the centre, side and rear outputs. The line/mic input's analogue-to-digital converter (ADC) is a Cirrus Logic CS5361. The PLX chip and these DAC and ADCs at least partially explain why this more expensive card has the supposedly inferior AV100 audio processor compared to the allegedly superior AV200 chip of the cheaper Xonar DS.
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The back of the card has the usual five 3.5mm stereo ports for 7.1 analogue audio out, plus a mic/line in. The latter doubles as an optical S/PDIF out, so you'll have to connect the front panel header if you want to use a microphone at the same time as S/PDIF digital audio output. The card's overall SNR ratings are better than those of the Xonar DS or the Creative Sound Blaster X-Fi Titanium, at 116dB for the front output channels and 112dB for the rest. Sample rates of analogue playback and recording are up to 192KHz/24-bit.
Like the rest of Asus's range, the Xonar DX comes with a wide range of accompanying drivers and software. These range from the useless (VocalFX voice alteration) to the brilliant (EAX 5.0 emulation and Dolby Digital Live). Although Dolby Digital Live doesn't provide HD surround sound audio - you'll need a Xonar HDAV for that – the Xonar DX does an excellent impression with its on-the-fly 5.1 AC3 conversion and S/PDIF output. This makes for an immersive movie-watching experience.
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Audio quality for both movies and music is lush and balanced, although, like the other cards in this roundup, it lacks the scintillating quality of Asus's specialist audio cards, such as the Xonar Essence ST. That said, this card is half the price of the Essence ST, and definitely has the best music reproduction of any of this sub-£100 group. However, The Xonar DX is not perfect for everything - despite clean recording quality, audio production is clearly a secondary feature, with the single line input sharing a port with the optical S/PDIF. Then again, that's not the market Asus is going for here.
Although the Xonar DX has been around for a while, it's held its place as one of the best sound cards for £50 or so. With excellent continued driver support and a decent price, this little PCI-E card sets the standard that the rest of the budget sound card market has to meet, and does so with great style.