The RightMark Audio Analyzer suite is designed for testing quality of analog and digital paths of any audio devices, be it a sound card, an MP3 player, a consumer CD/DVD player or an acoustic set. The results are obtained by playing and recording test signals passed through the tested audio path by means of frequency analysis algorithms. The latest version of RightMark Audio Analyzer can be found here.
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The ASUS Sabertooth X58 audio performance according to Rightmark Audio Analyzer is only Average, though not being an audiophile it sounds great to me.