In our last couple of sound card reviews, we've noticed some odd behavior from products based on Creative's X-Fi audio processor in RightMark Audio Analyzer's frequency response tests. The X-Fi had no problems with the frequency response test when we initially reviewed the XtremeMusic more than two years ago. However, that was with RMAA 5.5 and Windows XP. RightMark Audio Analyzer is now up to version 6.06, and at least under Windows Vista, X-Fi frequency response curves are all jacked up. Here's what I mean.
In the graph above, taken from RMAA 5.5 under Windows XP, the X-Fi XtremeMusic's frequency response curve looks fine.
Fast-forward to Windows Vista with RMAA 6.06, and the frequency response curve is a mess. These results were taken from the exact same sound card and associated driver control panel configuration.
This behavior goes beyond just the XtremeMusic, as well. Again in Vista, the frequency response curves for the X-Fi Fatalty and Auzentech's X-Fi Prelude are all over the map.
What's particularly odd about these results is that they only appear in RMAA "loopback" tests that simultaneously play back and record the test signal on the sound card. When we use a separate sound card on a second test system to handle the recording, the response curves even back out.
The fact that X-Fi frequency response is unaffected with these straight playback tests is even more curious considering we actually used a second X-Fi as the recording card on our secondary system. So there's nothing wrong with X-Fi frequency response on the playback end or on the recording end—only when the two are used together in a loopback test on a single card.
We've contacted Creative about the issue and hope they'll respond with a solution. However, unless you're in the habit of playing back and recording audio simultaneously, you shouldn't be affected by the X-Fi's poor frequency respose in RMAA's loopback tests.