Most people's minds, always feel Dolby Digital (Dolby Digital Sound) should be the multi-channel, or that should contain the main channel, a center channel, rear and subwoofer channel 5.1-channel surround sound, But this is not the case . There are many possibilities for recording Dolby Digital sound in DVD movies . It can be the most simplified mono , or the well-known 5.1 channel , and of course there is a Dolby Digital between them. Stereo, Dolby digital 4.0BDolby digital 5.0 ...... etc .. in this must be added a mention, is the sound of DVD storage methods, in addition to Dolby digital, DTS can also be a digital surround sound, European MPEG 2,? SONY development the SDDS, or for the demands of high-quality stereo PCM digital format, but mainly use DVD to record Dolby digital sound, and create rich surround effect.
Here are a few of the Dolby Digital formats that may appear on the DVD . Let's explain them one by one :
1. Dolby Digital Mono: Dolby Digital mono sound has only mono effects , not enough to form stereo , mostly in older movies . When filming , mono sound is stored as AC. -3 format , so when playing with Dolby Digital system , only the middle channel sounds . This sound quality performance is undoubtedly tedious , because even the basic three-dimensional sense is very lacking , let alone the surround effect .
2. Dolby Digital Stereo: Dolby Digital Stereo sounds the two-channel stereo signal in AC-3 format , so when playing back in the Dolby Digital system , you can sound from the left and right channel speakers of the main channel. This is in fact quite close to our common two-channel system (which is the same for normal audio) , which can construct a stereo sound field , but the sound of Dolby Digital is compressed and somewhat affects the sound quality. The CD record is uncompressed and has the potential for high sound quality .
3. Dobly Digital Surround: Dolby Digital Surround Sound using matrix encoding, the main channel, a center channel and a rear surround channel into two channels pressed, and stored as in AC-3 format. When Dolby Digital system decodes and plays , you can hear the complete five channels , but the surround sound is single sound , not stereo . There are not only four speakers , how can it be five channels? That's because the surround channels behind the general home theater system are both channels . Here, the two channels are presented in a single sound , that is, the two speakers make the same sound .
4. Dolby Digital 4.0: Dolby Digital Surround Sound 4.0 encodes four independent channels , including the main channel, center channel and surround channel, into an AC-3 format for storage into DVD movies , so through Dolby Digital When the system decodes and plays , you can hear the complete five channels . At this time, the surround channel is an independent mono recording . At first glance , Dolby Digital Surround and Dolby Digital 4.0 seem to be the same, but it is not . Strictly speaking to, Dolby Digital surround uses to store data of two channels, the center channel and the surround channel are deduced from the two channels, calculated; Dolby Digital 4.0, but it is the use of four acoustic solid The way to store the main channel, center channel and surround channel is still somewhat different .
5. Dolby Digital 5.0: Dolby Digital Surround Sound 5.0 encodes five independent channels , including the main channel, center channel and rear channel, into an AC-3 format for storage in DVD movies , when through Dolby Digital When the system decodes and plays, it can restore the complete five channels . At this time, the surround channel at the rear starts to take the independent two-channel route , providing more accurate positioning and sound field surround feeling .
6. Dolby Digital 5.1: Dolby Digital Surround 5.1 In addition to the main channel, center channel and rear channel , plus a subwoofer channel , then encode the six channels into AC-3 format . Therefore, in order to decode Dolby digital playback system, you can listen to five channels plus a subwoofer channel. For this subwoofer channel cover only the low-frequency range, not the complete frequency range, 0.1 to view it. Remind readers that not all DVD movies provide bass channel sound . Therefore , if the low frequency of your main channel speaker is heavy enough , you can also play the effect of extending the low frequency. It is not necessary to add this subwoofer. Although Dolby Digital has many possibilities and includes different output channels , in general , we simply use Dolby Digital to represent Dolby Digital 5.1, which is 5.1 channel Dolby Digital or AC-3. As for the two-channel Dolby Digital 2.0, most of them will be called 2 Channel Dolby Digital.
7. PCM high-quality digital sound : Compared to the above several methods of compressing data using AC-3 encoding technology , DVD can also use PCM format to store uncompressed two-channel signals , without any compression loss. Processing the program , so you can get the best sound quality . In fact, this PCM recording format is the same as CD recording , but because of the huge space and speed advantage of DVD, you can boldly use higher sampling rate and resolution , so you can Provides much higher performance than traditional CDs.
8. DTS digital surround sound : also belongs to the 5.1 channel surround effect , DTS uses the compression technology different from AC-3 to store the surround sound to the DVD. The system must have dts decoding ability to be hidden in the DVD. the 5.1 release. the same is 5.1, DTS with Dolby Digital 5.1 What is the difference? The biggest difference is that the two use different 'algorithms' , which is to use different ways to compress the sound of 5.1 channels .
Dolby Digital 5.1 can press the same data less and take up the least space . Conversely , because DTS does not deliberately pursue the most powerful compression capability , it also has the opportunity to save more information . If it is handled properly , it can provide very much. Superior performance .
Coding method Dolby Digital (Dolby AC-3) Dolby Pro Logic DTS
Processing method Each channel independent digital coding analog matrix operation each channel independent digital coding
Recording channel number * 5.1 channel 2 channel 5.1 channel
Play channel number 5.1 channel 4 channel 5.1 channel
Monophonic surround channel whether a stereoscopic perspective
Surround channel bandwidth 20Hz~20KHz 100Hz~7KHz 20Hz~20KHz
Separate subwoofer channel Yes No Yes
Transmission rate 448kbps** N/A 1536kbps
Note: * indicates the number of channels ( Channel ) to be used during recording . For example , although Dolby Prologic is a four-channel surround system , it can actually use the matrix to surround the center channel and surround. The channel is hidden in two channels , so it only takes two channels to store . ** This is the average on a regular DVD, but the actual transfer rate is subject to change .
Today's overlord A-C3
AC-3 was originally developed for use in the cinema, AC-3 sound film because it is limited space, so the AC-3 audio data is stored on film, intermediate perforations and perforations, this part of the real space Too small , so Dolby engineers had to remove places that they thought were inaudible to save space , and this destructive compression would still cause distortion , but in order to accommodate the limitations of the original equipment , this It is also a last resort
The AC-3 uses 6 speaker modes . Except for the subwoofer , the rest are full-band Stereo channels , 48KHz, 16bit, and each channel is recorded as a separate microphone during live shooting , so the surround back of AC-3 The channel has complete positioning capabilities
AC-3 data flow, the two channels is 192Kbps, about one of the uncompressed data size of 8 minutes, flow was 5.1 384Kbps ~ 448Kbps, 640Kbps to lift up, the larger the data traffic representative of a smaller The compression ratio , the sound quality will be better , and the details that can be heard will be more , but the Dolby AC-3 will control the S/N ratio very well , so the focus is on the amount of detail that can be heard .
Up-and- coming DTS
It is said that Dolby Digital stores the sound data in the middle of the perforations on the film. Because of the space limitation, a large amount of compression mode must be used , so some sound quality is sacrificed , but this limitation is used by the original small company DTS . a simpler approach, the approach is sound data into another CD-ROM above, and then synchronize it with the image of the like, so that not only increase the space, the data traffic may be relatively larger, but also will put audio data from a CD to replace, you can Bofang other language versions, is really quite convenient to theaters, it is also because of this DTS in the professional theater better than the Dolby AC-3.
In the LD era , because of the limitations of LD's innate specifications , it is not compatible with the 5.1- channel Dolby AC-3 and DTS. It can be said that fish and bear's paw can't have both , which also caused DTS 's failure in the home theater market , to the current DVD. Times , because the DVD 's large capacity can be compatible with AC-3 and DTS on a single disc , but because of some non-technical problems , DTS must use the PES format that is not compatible with the previous PCM format , although the digital output connector is The same , but the old DVDPLAYER can not recognize the PES format , so users who want to use DTS sound effects must replace the new generation of models to use DTS, which undoubtedly hinders the DTS route.
DTS at AC-3 with the difference that the size of the data traffic, data traffic has DTS 1536Kbps on a DVD, compared to 384Kbps ~ 448Kbps, or more than three times as much data traffic, even though the AC-3 to the limit The 640Kbps, DTS is still more than 2 times stronger , which makes DTS can hear more details than AC-3, the whole sense of space and movement will be better and clearer .
Costly THX
THX sound by George Lucas Academy Award winner of the invention, with Dolby Digital and DTS is a different concept of the product, although it is also a 5.1-speaker pendulum method can also be said to be the same, but it has the accurate positioning There are only three channels in front , and the surround back is just two Mono channels .
The spirit of THX is to improve the sound quality of the original cinemas and home theaters , and to correctly present the sounds that the original movie wants to express to the users who watch the movies in the cinema or at home , so THX for every link , such as DVDs , amplifiers , Speakers , even audio-visual space specifications have strict requirements , not a step , and because each device needs to be certified , so the cost of the certification is quite high , to enjoy the complete and correct THX sound , it is indeed Very big .
THX also has a fairly considerable place , because the center channel of the movie theater is located at the back of the screen , which will inevitably cause the attenuation of the high-frequency part , so the film will be deliberately gaining the effect of the high-pitched part during the recording of the film to make up for the penetration. The attenuation of the screen , so it is not appropriate if it is directly applied to the center channel in the home theater , because the center channel of the home theater does not need to penetrate the screen , so the high frequency part will be too abrupt. , lost the effect that the film originally intended to express .
THX is also a 5.1- channel specification . The speaker position is roughly the same , but its true positioning effect is limited to the front three channels , and the surround back channel is only Mono sound .
Note: The new version of the THX specifications, has a complete surround positioning, can be used with AC-3 / DTS
What is the comparison between THX and the first two ?
Since THX has different concepts from AC-3 and DTS, the features are different . The positioning effect is not as independent as the rear surround stereo sound of the former two , so the standpoint is different . What is the comparison ? THX is basically for A requirement for equipment and environment is also considered as a post-processing. It is certified by THX and represents a certain level of sound performance . Of course, THX can complement AC-3 and DTS with AC-3 or DTS. The system , together with the certification of THX , is even more powerful . Of course, AC-3 and DTS equipment are as standard as possible , in line with THX 's standard for " sound quality performance ", of course, you can take THX for certification .
SDDS sound
SDDS full name is Sony Dynamic Digital Sound, of course, is that developed by Sony, which uses the same source and MD feeling coding compression technology, because the United States eight pictures of Columbia / Samsung (Columbia / Tri Star) companies under Sony Corporation's, of course, we will launch a copy of this sound, but at a higher share of Dolby Digital and DTS shadow, SDDS current influence is relatively low. and 5.1-channel Dolby Digital and DTS difference is, SDDS In the 7.1- channel system , the two channels are the center left channel and the center right channel , which means that the SDDS has five channels in front . The DTS follows the footsteps of Dolby Digital and officially enters the home surround system. market, SDDS also have a chance to enter the oar in the home market? At present, Sony has no action in this regard . In the short term, it is impossible to try SDDS sound at home .
DTS ES Discrete 6.1
When most of the AV fans have yet to have a 6.1 or 7.1 system, DTS and 2000 June 15 this year, officially announced the launch of the new 6.1-channel system, this new system is called DTS ES Discrete 6.1. Discrete what it means What? It is the meaning of separation and independence .
That is to say , DTS ES Discrete 6.1 records the surround back in a separate track (in fact , a separate extension is added to the 5.1- channel core area of ​​the master ) , without first being mixed by matrix coding. Programs for left and right surround channels .
Since there is no matrix coding, of course, there is no need to separate the channels from left and right surround decoder. In fact, we are currently in use 5.1 per channel is independent of, and not mixed with each other. In order to merely "expedient The surround back channel uses the old method of matrix blending to process the surround back channel . According to DTS 's Lorr Kramer ( Director of Spacial Technical Projects ) , they originally thought that the surround back channel was placed in a matrix. In the left and right surround channels, it is not appropriate , so I have long wanted to treat the surround back channel as an independent channel , which is not technically difficult .
Plus electronic E-Cinema movie after movie theater playing the (also known as Digital Cinema Digital Cinema) has been determined to use independent rear surround channels, DTS system share in the cinema and no less than the Dolby system, so be sure A separate surround back system will be used in the cinema . In this case , DTS simply decided to introduce a separate surround back channel system in the home market , which is the DTS ES Discrete 6.1 system .
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