OSNews

The MPEG AAC codec operating at 320 kbit/s shows an “Excellent” quality level on average, however it performs less well for “applause” (i.e. “Good”). Unfortunately, AAC could not be tested at 448 kbit/s, therefore a direct comparison with Dolby Digital and Windows Media is not possible at that bitrate.

Nevertheless, HE AAC codec gives really remarkable results. For bitrates equal and higher than 160 kbit/s, the average of all ten test items was found to be in the region of "Excellent". This means that the mean value of HE AAC is similar to the mean value of the above mentioned codecs operating at almost 3 times higher bitrate! On the downside, HE AAC gives a rather unbalanced behaviour, as "applause" is always in “Fair” region, independently of the selected bitrate.

Equally remarkable is the quality performance of HE AAC at 128 kbit/s. In spite of extremely low bitrate (for multichannel audio!), it scores systematically between “Good” and “Excellent”, with the exception of "applause" which is again in the “Fair” region only.

It can be concluded that, at the moment, the MPEG HE-AAC seems to be the most favourable choice for a broadcaster requiring a good scalability of bitrate versus quality, down to relatively low bit rates. In addition, the AAC-based codec family offers excellent audio quality at higher bitrates, e.g. at 320 kbit/s (with the exception of "applause"). Our study shows that excellent quality (on average) can be achieved even at half the bitrate, i.e. 160 kbit/s, or even less, for all test items except for the most critical items.