Influences of SBR starting frequency on the encoding quality of HE-AAC

• Main Authors: Wei-Hsun Huang, 黃威勳
• Other Authors: 尤信程
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/9t7q4v

碩士 === 國立臺北科技大學 === 電資碩士班 === 100 === HE-AAC use Spectral Band Replication (SBR) module to improve the compression efficiency of perceptual audio codecs. SBR module transposes low frequency components to high frequency components, and then adjustment the high frequency components spectrum to reconstruct the audio signal. Thus, it allows for a much higher audio quality at low datarates. HE-AAC decides the spectral band replication range that depends on SBR module according to sample rate and datarate. After testing via EAQUAL, several kinds of music type use the same start frequency to encode audio file according to sample rate and datarate, the results of audio quality were not the best encoding quality. Thus, encoding quality was influenced by SBR starting frequency. We propose a method to decide SBR starting frequency. The method calculates the distortions and energies ratio of AAC low band part in HE-AAC, and depends on that, we adjust starting frequency dynamically during eocoding process. After many experiments via EAQUAL, versus to reference encoder, we got better audio quality in new encoder, and encoding quality was very close to the best encoding quality.