從學術上講,HE-AAC混合了AAC與SBR技術。SBR代表的是Spectral Band Replication(頻段複製)。SBR的關鍵是在低碼流下提供全帶寬的編碼而不會產生產生多餘的信號。傳統認為音頻編碼在低碼流下意味著減少帶寬和降低採樣率(見MP3 FAQ #7)或產生令人不快的噪音信號。SBR解決問題的方法是讓核心編碼去編碼低頻信號,而SBR解碼器通過分析低頻信號產生高頻信號和一些保留在比特流中的指導信號(通常碼流極低,~2 kbps)。這就是採用無SBR解碼器的原因,這樣你的帶寬(frequency response)(頻率響應)會被嚴重浪費。這也是為什麼被叫做Spectral Band Replication的原因,它只是增加音頻的帶寬,而非重建。
描述The zipped file contains the source code for third party copyrighted software licensed under the GNU General Public License ("GPL"), which software may be used in WD TV™ Media Player. A copy of the GPL may be found below or at http://www.gnu.org/.
http://www.hdmania.org/forum_posts.asp?TID=7103&PID=85041
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Good news! As bensons has posted -- we released the WDTV GPL code for your viewing pleasure and the new firmware update (1.01.00) is also being readied for download - I finalized and approved the release today. It should be online early next week.
Many of your requests were considered and we worked hard to get them into this release. There are close to 40 new features, enhancements and fixes that will be part of this release and a few surprises that I hope you all find.