Popularization of basic audio knowledge (VII)

　　Whenever you enjoy the climaxing music in a DVD, have you ever thought about collecting these beloved music clips and enjoying them separately? Or when a friend has a top-notch DVD audio test disc and refuses to lend it, you want to take it back to test your own audio equipment? For some music lovers, they often encounter the same problem. For example, ever since I saw the DVD of "Fantasy 2000", I have always wanted to extract the exciting music from it and make a CD to enjoy it slowly with my eyes closed; not only that, I often want to burn all the thrilling multi-channel special effects in "The Prince of Egypt", "Terminator 2" and "The Matrix" on a disc so that I can take it to an audio and video equipment store to test the machine...

　　All of this is now easy to achieve. All you need is a DVD-ROM and an ordinary CD burner, and then follow the methods in this article to burn your favorite multi-channel audio tracks from the DVD to a CD-R (RW), and make a DTS CD to take home for listening and testing.

　　DTS 和 DTS CDl

　　First, let's take a look at what DTS CD is :

　　The so-called DTS soundtrack uses the 5.1 channel standard after being encoded by DTS (Digital Theater Systems). The maximum encoding flow of DTS is the same as that of LPCM, that is, 48000*16*2=1536000bps=1536kbps per second. Relatively speaking, this is much larger than the 448kbps provided by Dolby Digital (AC3), another popular multi-channel encoding system. In other words, DTS has much less distortion in the compression process of multi-channel sound products. This feature gives DTS an inherent advantage in multi-channel encoding systems. Because of this, DTS-related products and equipment are increasingly favored by consumers in the market.

　　As for DTS CD, as the name implies, it is an audio-CD with DTS soundtrack. Its storage method is the same as that of ordinary music CDs, with 16 bits and 44.1kHz sampling frequency. However, the actual content recorded in DTS CD is not the PCM sampling signal of ordinary CD, but the DTS-encoded soundtrack signal. Since the DTS CD file recording format is compatible with ordinary CDs, it can be reproduced, produced and played in the same ordinary way as music CDs. In addition, most DVD players and CD players with digital output functions on the market currently support direct output of DTS digital signals. In addition, most audio enthusiasts or equipment stores already have DTS decoding equipment, which makes it easy and convenient to enjoy DTS CDs.

　　Extract multi-channel audio tracks from DVD files

　　To make a DTS CD from a 5.1 channel audio track on a DVD, you need to first copy the digital audio signal from the DVD to the computer hard disk. This is because the DTS encoding and CD burning work must be completed on the computer, and copying the digital information to the hard disk is the most basic condition for completing the DTS CD production. Therefore, we also need to have a basic understanding of the DVD data structure.

　　If we use a DVD-ROM to open a DVD video disc, we will see a file directory named "VIDEO_TS". The main video, audio, subtitle data, time code, paragraph segmentation information, etc. in the DVD video disc are all stored in various VOB files under this "VIDEO_TS" directory. Naturally, the multi-channel AC3 audio tracks in the DVD video disc are contained in these VOB files.

　　It is not complicated to separate the various audio tracks contained in VOB. Many software can complete this task. Here we take VOBRator as an example to roughly understand the basic principle of separating audio tracks. After you have a certain understanding of this step, you can apply it by analogy and use various advanced DeCSS software you like.

　　After opening the VOB file on a DVD disc (or hard disk) with VOBRator, a tree-like list of DVD track information will appear in the "Streams" column. This list lists all the contents contained in the VOB. When selecting each item, the information column on the right will also display the specific information of the track: such as sampling rate, number of channels, bit rate, etc. What we need is to let VOBRator output specific audio tracks according to our needs.

　　In the entire tree list, we must first select ****.VOB at the "root" and click the "include in output" option on the right to cancel it. Then you should see a cute little red cross on all the items. Then, select the 5.1-channel AC3 audio track you want to capture, and also click the "include in output" option on the right to make this track the only one selected. Now, VOBRator will obediently process the selected audio track according to your requirements. Click "DeMUX" (that is, directly separate the data), and VOBRator will output a ****.ac3 AC3 format multi-channel audio track file.

　　You can use the same method to continue to capture your favorite audio track segments, and finally collect these AC3 files together, further encode them into DTS, and import them into CD burning software to further burn them into DTS CD.

　　Channel separation

　　After obtaining the 5.1-channel AC3 digital audio file, the next goal is to separate each channel in the digital audio file for re-encoding. There are a series of professional or amateur software that can be used to edit and separate the channels in AC3 audio files. Among them, the most famous one is the powerful Dobly Digtal AC3 editing software launched by Sonic Foundry, a professional audio editing software development company - Sonic Foundry Soft Encode.

　　Sonic Foundry Soft Encode can decode and encode AC3 audio channels, and we need to use it to decode AC3 files and output WAV audio files recorded in PCM format that can be recognized by the encoding software. Of course, PCM-WAV itself does not support 5.1 multi-channel mode, and DTS encoding software cannot recognize 5.1-channel AC3 files. Therefore, we must separate each channel in the AC3 file into a WAV file. Although this process is cumbersome, it is not difficult:

　　Open Sonic Foundry Soft Encode, first enter [Decode Setting] under the [Option] menu, and confirm that the "Dynamic Range Compression" is in the "RF remod mode" mode to ensure the correct decoding effect. Then click [Open...] in the [File] menu. Note that you must select "Decode to PCM" in the open mode switch next to the file type and confirm to open the AC3 audio file. This process may take a while, as the CPU needs to decode the AC3 file and save it in PCM format to a temporary folder. The waiting time is related to the CPU's computing speed. When the decoding is completed, the 6-channel audio tracks will be neatly arranged in the main window of Sonic Foundry Soft Encode.

　　At this time, if we are lazy and browse the directory where Sonic Foundry Soft Encode stores temporary files, we will see that there are 6 *.tmp files lying there quietly. They are actually six-channel audio files arranged in the order of "left", "center", "right", "left rear", "right rear", and "subwoofer". We just need to copy these files and rename them as WAV files, and then we can directly give them to the encoding software for use.

　　Of course, the lazy method above has a flaw, which is that it is easy to confuse the order of the six channels. Therefore, a proper method should be prepared as a backup: After the AC3 file has been opened, right-click on the channels that do not need to be retained one by one, and select "Delete" to delete them, so that Sonic Foundry Soft Encode only retains one "left front" channel. Click the "Save as..." icon to save this single "left front" channel as a standard PCM-WAV file for future use. After that, use the same method to save the "center", "right front", "left rear", "right rear", "subwoofer" and other channels separately.

　　Regardless of which of the above methods we use, after we obtain the separated channels, we can start encoding these 6 channels into DTS format.

　　DTS Encoding

　　DTS encoding software is rare, and the only software available to ordinary users may be the SurCode series from Minnetonka. In the SurCode series, there is a "SurCode CD Pro DTS" that is specially designed for making DTS-CDs. Users only need to provide the WAV files of each channel to the software, and SurCode CD Pro DTS can easily combine and encode them into 44kHz DTS format WAV audio files that can be used for DTS-CD burning.

　　The interface of SurCode CD Pro DTS is also very simple and intuitive. We just need to fill in the output file name at "Destination...", and then add the PCM audio track and channel files just separated from AC3 one by one according to the prompts on the interface, and then we can immediately click the "Encode" button to start DTS encoding. SurCode CD Pro DTS will also directly output the "disguised" DTS-WAV format, making it more convenient for other CD burning software to burn DTS CDs.

　　l Burning

　　At this point, the key issue of converting multi-channel information into a format that can be used to burn DTS-CD has been solved, and the remaining work can be said to be very easy. The method and process of burning DTS-CD are exactly the same as burning ordinary music CDs. For example, using the popular burning software Nero, just create an Audio CD project, drag the collected DTS-WAV files into the Audio column on the left according to your preferences, and click the "Burn" button in the toolbar, and our first DTS CD is done. If it is a direct-drag burning software such as EZCD or Drop CD, it is even simpler. Just drag the DTS-WAV generated by SurCode CD Pro DTS into the CD icon.

　　With the possibility of copying and making DTS CDs by yourself, you can enjoy the thrilling feeling of 5.1 channels with fewer restrictions. As for the enjoyment of the soul, the cultivation of art, and even the fever of the equipment, you can do whatever you want without any constraints.

　　Notes

　　When listening to DTS CD, you need to connect the digital output (SPDIF or optical output interface) of the player to the corresponding DTS decoder or decoding amplifier, and then the corresponding DTS decoder or decoding amplifier will decode the digital signal to obtain the wonderful DTS 5.1 channel output. If you play on a computer, you need to install a DTS-supported player such as PowerDVD to correctly play back the multi-channel audio signal of the DTS CD.

　　Basic audio articles

　　DTS is a hot topic in the home theater market this year. AV receivers with built-in Dolby Digital/DTS dual decoding functions have become the new favorites in the market, and DVD players with built-in DTS 5.1 decoding output have also been launched one after another. Next, let's learn about the basic situation of DTS and its technical background.

　　DTS technology is closely related to the American gold medal director Spielberg and the American Universal Studios. The DTS headquarters is located in Hollywood, USA, and has branches in Brussels, Belgium and other places. The company's main structure is divided into two parts: the professional "digital theater system" mainly for the encoding and decoding of movie music recording sites and cinemas, and the consumer electronics "DTS technology" mainly for the development of home decoders and the introduction of DVD/LD/CD and other package software.

　　DTS technology was created by Mr. Dreberg in January 1993. In the early 1990s, when the digital soundtrack of movies was first proposed, Dreberg proposed the solution of using CD-ROM to record compressed sound signals. At that time, although the technology of writing digital sound signals directly to film had been developed, the reading method of this technology often resulted in reading errors and the stability was not ideal. However, CD-ROM has been widely used in the computer field, with a stable supply and low price. When using CD-ROM to record, you only need to install the CD-ROM with recorded audio digital signals when showing the movie, and there is no need to record on traditional film.

　　After the development of this technology, once it was announced in the film industry, it was immediately highly valued by the great director Spielberg and Universal Pictures, who decided to first try to use DTS technology in the large-scale science fiction movie "Jurassic Park". As a result, "Jurassic Park" conquered the audience with its realistic special effects and stunning digital surround sound effects, and set off a "Jurassic whirlwind" with a global box office revenue of 920 million US dollars, becoming one of the most popular movies in history, second only to "Titanic" in 1997 and "Star Wars Prequel" in 1999. Spielberg spoke highly of DTS technology, and Universal Pictures was also very optimistic about the prospects of DTS. Therefore, Spielberg and Universal Pictures even cooperated with Derryberg to establish DTS.

　　Since Spielberg first used DTS in "Jurassic Park", many Hollywood movies have also begun to use DTS's digital surround sound system. Many directors, production staff and mixers believe that DTS is the system with the best sound reproduction, which can even compete with the original excellent 70mm film magnetic track soundtrack. Theater operators also believe that the movies produced by DTS are full of charm, and DTS technology is easy to operate, so it has gained absolute support. In the fifth year of DTS's advent, there are more than 200 movies with DTS soundtracks, and almost all new Hollywood movies have both Dolby Digital and DTS soundtracks. As a movie terminal, the number of cinemas using DTS sound reproduction systems is rapidly increasing. Currently, more than 60% of cinemas in North America are equipped with DTS sound reproduction systems, more than 25% in Europe, and 5% in Asia. These numbers are still increasing. It can be said that DTS has become a leader in digital surround sound tracks alongside Dolby Digital and has received strong support from most cinemas in the world. Together with Sony's SDDS, it has become one of the three major digital surround sound systems in the film industry.

　　In the field of consumer electronics, the chip for DTS decoder was developed in early 1996. About a year later, many audio product manufacturers began to adopt this technology. By the end of 1998, there were 12 manufacturers authorized to manufacture independent DTS decoders or AV amplifiers with built-in DTS decoding functions. At present, almost all AV amplifiers on the market with a price of more than 4,000 yuan have built-in DTS decoding functions.

　　As for DTS software, in January 1997, DTS-LD discs of "Jurassic Park" began to be sold, especially those of UNIVERSAL, and later, DVD movies of DTS also began to be sold. However, in terms of quantity, DTS discs still lag far behind Dolby Digital versions.

　　For LD, the data transmission rate of Dolby Digital is 448kbps, while DTS's signal compression ratio is more than three times the information volume of Dolby Digital, which is roughly the same as 16bit/44kHz/2-channel linear PCM, about 1411kbps, so DTS data occupies more space. In Japan, EFM digital sound is stipulated as the standard format for LD, and there is no space to accommodate DTS audio data. Therefore, Japanese versions of LD do not even have DTS versions. For DVD, the typical data transmission rate of 5.1-channel Dolby Digital format is 384kbps, and the transmission rate of DTS sound recorded on DVD is actually roughly the same as 48kHz/16bit/2ch linear PCM sound, reaching 1536Kbps, which is higher than the transmission rate of DTS signals recorded on LD and CD (1411kbps). The sound of DTS-DVD is generally sold in the form of a combination of DTS 5.1 channels + Dolby Digital 2 channels. DTS is different from Dolby Digital in that it has 5.1 channels, while Dolby Digital can flexibly choose from 1 channel to 5.1 channels. Since DTS has a higher data rate than Dolby Digital, DVD movies in DTS format of about 2 hours often omit some functions such as multi-language and multi-angle or additional content such as film highlights and making-of specials. It is also difficult to have Dolby Digital 5.1 or PCM sound for selection at the same time, unless a larger capacity double-layer structure DVD disc or double-sided DVD is used to ensure the quality of the picture. Otherwise, it will not meet the requirements of directors and filmmakers for DVD quality. Therefore, except for "Saving Private Ryan", many works of the great director Spielberg (such as Jurassic Park, Lost World, etc.) have never met AV enthusiasts until recently, when the long-awaited "Jaws" special edition DVD was released.

　　The sound designers who participated in the DTS production process indicated that DTS can further expand its application in movies, music, etc. Yael Hud of Enterprise studio believes that 5.1 channels are most effective for live sound sources and can create a sense of presence that cannot be achieved by 2-channel mixing of broadcast recordings. He has won the production award 7 times. As a Universal Studios that has always supported DTS technology, the sound design studio composed of Max Stroh and Clark Landy has 20 years of rich experience in film mixing and has produced famous blockbusters such as "Speed", "Waterworld" and "Twister". They said that the competitiveness of DTS and Dolby Stereo's LT, RT Master, Dolby Digital and SDDS first started with the mixing operation. The 6-channel MAC Master they designed is all formatted.

　　When all movies and theaters are replayed with digital soundtracks, bold mixing that enhances the surround sound effect is possible. The revolutionary significance of digital soundtracks in terms of sound quality, especially in expanding dynamics and ensuring high signal-to-noise ratio, is equally important. This is paid great attention to when making DTS Master. When encoding, the signals below 140Hz of the surround channel must be separated from the subwoofer channel. Of course, if this is not the case, the surround channel can also be set to the full range. The sound processing in "Speed" and "Twister" is almost carried out according to this setting.