What is AC3

In 1994, Japan Pioneer Corporation announced the development of a new surround sound system in cooperation with Dolby Laboratories, and named it "Dolby Surround Audio Coding-3" . In early 1997, Dolby Laboratories officially changed the Dolby AC-3 Surround Sound to Dolby Surround Digital, often referred to as Dolby Digital.

It is Dolby has developed a new generation of home theater multi-channel digital audio system. The Dolby Pro Logic System is an analog system. Its four channels are decomposed from the two channels after encoding, so it is inevitable that there is a disadvantage of poor resolution, low signal-to-noise ratio, lack of stereoscopic effect on surround sound, and narrow frequency band of surround sound. AC (Audio Coding) refers to digital audio coding, which abandons analog technology and uses a new digital technology.

The surround sound system provided by Dolby Digital AC-3 consists of five full frequency domain channels plus one subwoofer channel, so it is called 5.1 channels. The five channels include the front "left channel", "center channel", "right channel", posterior "left surround channel" and "right surround sound Road ". The frequency range of these channels is 3-20000Hz for full frequency domain response. The sixth channel, the subwoofer, contains some extra bass information, making some scenes such as explosions, percussive sounds, etc. better. Since the frequency response of this channel is 3-120Hz, it is called ".1" channel. The information of the 6 channels is digitized in the process of production and restoration, the information loss is very small, and the details of the whole frequency band are very rich.

Dolby Digital AC-3 is a multi-channel surround coding system developed according to the feeling. sound. It divides the frequency of each kind of sound into many narrow frequency bands according to the auditory characteristics of the human ear. In the encoding process, it analyzes according to the principle of acoustic psychology, retains effective audio, deletes the multi-made signal and various noise frequencies. To make the reproduced sound more pure and the separation is extremely high.

The Dolby Digital AC-3 system can be used with front left and right speakers. The center speaker produces a very deep and well-defined sound field with two rear or side surround speakers and super The low-speaker expresses a wide and wide sound field, and the information of the six channels is all digitized during the production and restoration process, and the information loss is small. The full range of details is very rich, with true stereo.

Dolby Digital AC-3 has good compatibility, in addition to its own decoding, it can also provide Dolby Pro Logic decoding services. As a result, Dolby Pro Logic software, which is currently in production, can be reproduced using the Dolby Digital AC-3 system. Because the coding of the Dolby Digital AC-3 system is very flexible, it has many formats. It is currently used in the United States as a high definition television (HDTV) audio system, and the latest DVD player also includes the Dolby Digital AC-3. Therefore, the Dolby AC-3 surround sound system may be a promising technology.

AC-3 music file format

AC-3 was originally developed for use in cinemas. AC-3 sound effects are limited because of the space of the film, so the AC-3 sound data is Stored on the film, in the middle of the perforations and perforations, the space in this part is too small, so the engineers of Dolby had to delete the places they thought they could not hear, so as to save space, this destructive Compression can still cause distortion, but in order to accommodate the limitations of the original equipment, this is also a last resort.

The AC-3 uses 6 speaker modes. Except for the subwoofer, the full range is the full-band Stereo channel, 48KHz, 16bit, and each channel is recorded as a separate microphone during live shooting. So the AC-3's surround back channel has full positioning capability.

The traffic of AC-3 data is 192Kbps for two channels, about one-eighth of the size of uncompressed data. The flow rate of 5.1 channels is 384Kbps~448Kbps, and the maximum can be increased to 640Kbps. The data flow represents a smaller compression ratio, the sound quality is relatively better, and the details can be heard more, but the Dolby AC-3 controls the S/N ratio very well, so the focus is on the audible details. How much is it or not.