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Comparing Windows Media Audio Professional and HE AAC Audio Coding In order to verify the performance of Windows Media Audio Professional (WMA Pro) at low to medium bit rates, Microsoft Corporation employed National Software Testing Labs (NSTL), the world's leading independent IT testing organization, to perform codec comparison testing. NSTL ran a proctored double-blind test that compared 64 kilobits per second (Kbps) WMA Pro (stereo) to the High Efficiency AAC Profile (HE AAC), an MPEG-4-based codec that claims to be the best mid-to-low bit-rate coder on the market.
NSTL encoded and then decoded 12 segments of audio, including both “critical” segments commonly used in the coding community to stress-test coders and also examples of popular modern music. NSTL used the low-bit-rate technology of WMA Pro and HE AAC coders available under the Nero 7 Ultra Edition digital media solution software package. The 12 segments were presented by a proctor in a double-blind test to 300 individual listeners of both sexes and over a wide variety of ages.
The test consisted of playing the original music clip, and then both the WMA Pro and the HE AAC clips, with the ordering randomized outside of the proctor’s knowledge and the identities of the coders hidden. Subjects were allowed to ask for replays of any of the signals, with the proctor controlling the playback computer in order to make the subjects’ task easier. Subjects were then asked to rate the clips (A or B, double-blind) as follows:A is much more like the reference than B A is more like the reference than B A is slightly more like the reference than B Both A and B sound equally like the reference B is slightly more like the reference than A B is more like the reference than A B is much more like the reference than A
When all 300 subjects’ responses to the 12 segments are combined, 37% of the listeners preferred WMA Pro, 34% expressed identical preferences, and 29% preferred HE AAC. In other words, 71% of all listeners indicated that WMA Pro was equal to or better than HE AAC.
For the responses that were not neutral, approximately 56% preferred WMA Pro and 44% preferred HE AAC. When the “slightly” responses and the “identical” responses were removed, 58% preferred WMA Pro, and 42% preferred HE AAC. Finally, when only the “much more” responses were considered, 64% preferred WMA Pro, and 36% preferred HE AAC. A detailed description of the test design, plan, and execution, as well as a complete set of results by response and by signal can be found in the NTSL report, which is available for download from this page.
In summary, it is evident that listeners prefer WMA Pro overall. What is more striking is that when considering the extreme answers, it is clear that more listeners prefer WMA Pro for signals that create a strong preference among listeners. WMA Pro outperformed HE AAC, and as such is an ideal technology for the mobile/cellular market.
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