Asus Xonar D1 Reviewhardnrg -
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So immediately you see that the card is a lot shorter than a regular card, but almost exactly the same length as other consumer soundcards like the Audigy and X-Fi series. How do they manage to cram all the components onto a card about half the size? Well, spinning the card over, you see that unlike many designs, Asus chose to place some of the components on the back of the card to capitalise on the extra board surface that often gets left unused.
Each of the sockets on the backplate takes a 3.5mm jack, and is gold-plated. The labelling of each socket is merely engraved/stamped, so there is no colour-coding to help you when connecting. It would have been nice to see Asus include a transparent overlay sticker, like the ones Creative use, with the colours at the side of each socket. You can see the top jack socket is a bit different from the rest, and this is because it functions electrically and optically, to serve the functions of Line/Mic inputs, and optical S/PDIF output. So, it's essentially the same as the "Flexi-Jack" of the X-Fi, but with the added bonus of optical.
Looking at the heart of the animal, we see an Asus branded APU, but it is in fact a C-Media OxygenHD chip (CMI8788) which is also used on other cards in the Xonar line, as well as other brands.
A Cirrus Logic CS4398 DAC is used for the front stereo output which promises a signal-to-noise ratio (SNR) of 120dB, and a maximum sample rate of 192kHz @ 24bit. Very respectable indeed! It is in fact the same DAC found on the X-Fi Elite Pro and other high-end audio equipment. For the analogue inputs, a Cirrus Logic CS5361 is used that has almost the same basic specs, but with a 114dB SNR. Still far from shabby. As a frame of reference, the SNR of CD-Audio is ~96dB, SACD is ~120dB, and DVD-Audio is ~144dB.
JRC make a range of op-amps, from hum-drum to pretty decent, and the NJM5532 is used for all the outputs, except the front stereo pair. It is regarded as one of the better op-amps in the world, well suited for high quality audio applications.
So what are the op-amps for the main stereo out and where the hell are they? They're on the back of the card. Texas Instruments R4850 are used here, and are characteristically very similar, with the main difference being that the voltage swing is greater for low load resistance. This means that the R4850 is better suited at driving headphones directly compared to the NJM5532. Also on the back is the Cirrus Logic CS4362 DAC which feeds the six remaining outputs. It is basically the same as the CS4382 DAC used on the X-Fi series, but with six channels instead of eight.
Ok, so enough talk about DACs and op-amps already! How about internal connectors? Well, the Xonar D1 has something that I wish all soundcards had: a front panel header! Seriously, why don't all manufacturers do this? The NEC components around the front panel header are miniature relays that act as mutes on the outputs, as well as switching from mic input mode to line input mode, etc. These relays can be heard engaging/disengaging at times, like right at the end of the Windows boot sequence, at power off, switching from mic to line as a recording source. It's a bit strange to hear relays clicking in your computer if you're not used to them. I have them in my amplifiers and they work on the soundcard to prevent the thumps you get when turning your computer on or off. Moving towards the back of the card, we have the Aux In which can be used for optical drives, TV cards, modems, etc.
The card has a S/PDIF out internally, which might strike you as unusual. Well, it sort of is! But, in a world that's gone "Hi-Def" flat-screen crazy, it's a welcome addition. This header lets you connect a small cable to a compatible graphics card, to combine the digital audio with digital video, which results in the full sound and picture coming through HDMI. This is something that people have asked me about many times, "how do I get the digital audio from the PC into the HDMI of my TV if it's coming from the graphics card?" And now you know. The final header on the card, JP2, is not documented, but it has been suggested that it is for a MIDI expansion card. This seems feasible, and tallies with the fact that this card has ASIO 2 support that is the most useful for low latency in musical applications when using external electronic instruments/equipment.
Enough with the hardware! Yes, yes, ok, here comes the software...