Introduction to AAC audio encoding
AAC audio coding format, the full name is “Advanced Audio Codec”.
This state-of-the-art, advanced encoding standard was jointly developed by Fraunhofer IIS (former MP3 standards maker), Dolby, AT&T, Sony, Apple, and other industry giants. AAC audio coding technology was formulated as early as 1997. At that time, it was used as one of the MPEG2-AAC audio coding specifications in MPEG-2. Later, it was used in MPEG-4 in 2000 (ISO 14496-3 Audio), so now it changed to the MPEG-4 AAC standard, that is, AAC has become one of the main members of the MPEG4 family, which is the audio coding system in the third part of MPEG4. AAC provides up to 48 channels of full-range audio. Among them, AAC audio coding is divided into nine specifications in different fields: MPEG-2 AAC main MPEG-2 AAC LC (low complexity) MPEG-2 AAC ××× (scalable sampling rate) MPEG-4 AAC main MPEG -4 AAC LC (Low Complexity) MPEG-4 AAC ××× (Scalable Sample Rate) MPEG-4 AAC LTP (Long Term Prediction) MPEG-4 AAC LD (Low Delay) MPEG-4 AAC HE (High Efficiency) AACPlusV1/V2( 3GPP ) Among them, the first three estimates are difficult to apply, and among the last six, LC and HE are the most used, so these two are mainly introduced:
MPEG-4 AAC LC (Low Complexity) is the most widely used specification, we call it “low complexity specification”, we call it “LC-AAC” for short, this specification can strike a balance in terms of coding efficiency and sound quality . at the half bit rate point. The so-called average bit rate refers to the bit rate between 96 kbps and 192 kbps. So if you want to use the LC-AAC specification, please try to control the bitrate within the range mentioned above. In this range, LC-AAC can completely beat MP3 with the highest quality LAME slow encoding mode at the same bit rate. In my opinion, whether it is a Walkman or streaming music over the Internet, it is recommended to use the LC-AAC 128kbps-192kbps encoding specification. MPEG-4 AAC HE (High Efficiency) AACPlusV1/V2(3GPP), we call it “High Efficiency Specification”, we call it “HE-AAC” or “AACPlus” for short, this specification is suitable for low bit rate encoding bits, because this specification also incorporates the type of SBR technology in Mp3Pro. When you need to encode audio files between 32 kbps and 96 kbps, it is recommended to prefer the “HE-AAC” encoding specification. With this spec, you can easily kill Microsoft formats like WMA9 and WMAPro within this range at the same bitrate. If you’re a fan of audio novels or radio dramas, consider the He-AAC specification, which can provide crystal-clear vocal dialogue even at a very low bitrate.
So if you need to encode AAC at relatively high bit rates (192kbps-384kbps or more), how should you choose? If your bit rate does not exceed 256kbps (eg: 192kbps-256kbps), “LC-AAC” can also be applied. If you really need a higher bit rate, choose the Main encoding (main specification). At high bit rate, AAC can also easily beat the very popular Lame MP3, even 320kbps CBR MP3 is not Mian-AAC’s opponent at all. Even many people believe that the LC-AAC medium bit rate, 192kbps CBR has reached the sound quality of 320 CBR Lame MP3. Of course, only the MPC format can compete with high-bitrate AAC, but the MPC format is too versatile. Having said that, there is no need to use high bitrate AAC, and Main-AAC will have problems in some general purpose or ××× players, because the sound quality of LC-AAC mentioned above is good enough, and the versatility is good. If you are an audiophile, just use lossless, like FLAC etc.
