Opening the door to HD: audio of the new generation of audio and video technology

Author: little monk afa published in: Period 2008-03 of Microcomputer

Preface

"HD" is a complete system, not a single standard or product. In the HD era, both video and audio must meet the HD standard. What is high-definition audio? What are the benefits of high-definition audio compared with normal audio? Starting from high-definition audio, the technology of high-definition audio has been unveiled layer by layer.

How to define HD Audio

1. Multi-Channel 5.1 surround sound, "pass line" of HD Audio"
Without a doubt, we live in a ring environment. In reality, the location and strength of the voice can be perceived by our ears. Since movie and television, people have been exploring how to get closer to the real and natural sense of hearing in addition to better visual experience. In the video and disc era, people began to get familiar with and understand the multi-channel, and found that the effect of multi-channel surround sound is far better than that of the previous two channels. Although not perfect, it sounds much more realistic.
In terms of experience, the closer it is to nature and truth, the closer it is to sound like an immersive voice, and the closer it is to the standard of HD audio. Therefore, we can say that to determine whether we have heard HD Audio, multi-channel 5.1 surround sound is the most basic. The 6.1 or even 7.1 multi-channel surround sound extended on this basis is closer to the definition of HD Audio.
However, from the "audio channel" perspective, the so-called HD Audio has already been implemented. Even many years ago, the audio standards of the DVD era have easily reached this level. In this way, there is no need to look into HD Audio again? Actually not.
2. Not only sound channels, but more details and higher fidelity are also important.
Is there enough sound channels, even the threshold for HD audio? This understanding is not completely correct, because the original intention of HD Audio is to give people a realistic sound effect. Multi-channel just creates a relatively real sound field for us. To obtain more sound details, ensure that the sound is more authentic, we must start with the sound encoding method-Adopt low-loss encoding compression, lossless encoding compression, or even non-compression processing methods. Therefore, industry giants of Dolby and DTS have launched their own high-definition audio encoding standards.
What they have in common is that compared with the most basic multi-channel audio in the past, they have a higher sampling rate, higher sampling accuracy, and several times the ultra-high bit rate of the previous generation of multi-channel audio format. This allows them to restore very high fidelity sound, exactly what the recording engineer in the recording studio heard. Combined with HD video signals, we can provide an unprecedented audio and video experience-what we see and hear are all high-definition effects.
As a matter of fact, the high-definition video source based on BD and hd dvd that we have reached through the network also contains different high-definition audio signals.

Resolve the conflict between compression ratio and sound quality-Dolby Digital Plus

HD Audio sounds better than traditional audio because it contains more information. However, this poses a problem-for the same program source, HD Audio must be stored in a larger space. At the same time, this feature puts pressure on network transmission. To alleviate the storage and transmission problems, it is effective to adopt a encoding method with a higher compression ratio, but the cost of using a higher compression ratio is a reduction in sound quality.
Dolby Digital Plus, also known as "DD + (Dolby Digital +) or DD plus", is the next-generation audio technology designed for HD programs and media. Similar to the previously used Dolby Digital Audio Encoding format, it also belongs to lossy encoding. However, as a new generation of Dolby audio encoding format, it features excellent encoding efficiency, allowing users to enjoy high-quality sound effects while saving storage space.
Dolby Digital Plus uses multi-channel surround sound output from separate channels to Process audio programs of up to 7.1 channels, and supports more than 8 channels. It has a very high bit rate, up to 6 Mbps (the highest bit rate in hd dvd is 3 Mbps, and the highest bit rate in BD is 1.7 Mbps ). At the same time, Dolby Digital Plus is highly compatible with your existing multi-channel audio system that integrates the Dolby Digital technology. Dubi digital signals can be output for playback on an existing digital system. It is worth mentioning that in the next generation of DVD standards, Dolby Digital Plus is set by hd dvd and BD as mandatory and optional audio standards.

Lossless sound and amazing results-Dolby TrueHD

People always expect better things. In terms of sound effects, we always want it to be as close as possible to the original sound. Although Dolby Digital Plus is excellent, it is a Lossy encoding format. Compared with Dolby Digital, it is only a step closer to the "original sound. Dolby TrueHD is a new generation of lossless coding technology designed for HD media.
Dolby TrueHD uses nearly 100% lossless audio encoding technology, so that each bit is exactly the same as the recording time to obtain sound effects that are similar to the quality of the recording shed mother band. It supports up to eight 24-bit/96 kHz full-band channels (theoretically up to 13.1 channels), with a bit rate of up to 18 Mbps.
In addition, like Dolby Digital Plus, HDMI1.3a is supported, and HD DVDs and BD are set to both mandatory and optional audio standards. Interestingly, DolbyTrueHD also features a user-friendly feature-dynamic range control (night mode ). This allows you to change the sound settings when playing the video, and reduce the peak volume level while ensuring the sound details, so as not to watch the video at night, others are influenced by big dynamic scenes.
The development of Dolby TrueHD largely benefited from an earlier technology-MLP Lossless compression (MLP Lossless ). MLP Lossless is a Lossless coding technology dedicated to DVD-Audio. It does not affect the Audio quality of high-resolution PCM (Pulse Code Modulation, pulsed coding Modulation, used for CD Audio, this effectively doubles the disk space so that the DVD-Audio can carry the same program's stereo and multi-channel Audio tracks. In fact, the highest standard-Master Audio of the DTS-HD will be involved later, also using a similar bit corresponding bit encoding method.

Flexible, high-quality audio solution-DTS-HD

At present, DTS in the high definition audio standard is DTS-HD, first of all, the DTS-HD technology is similar to Dolby Digital Plus, are based on 7.1 sound channel as the starting point, and can support up to 32 sound loop playback, at the same time, the bit rate will reach Mbps or above, thus achieving 8 ~ 192 kHz (16/24 bit) sampling range.
DTS-HD sampling method is flexible, taking into account the network transmission, and backward compatible with DTS, dts es, DTS 96/24 and other formats, DTS-HD and Dolby Digital Plus, Dolby TrueHD, also obtained the support of HDMI1.3a.
The DTS-HD follows the MLP audio technology and makes improvements. The new MLP technology continues the advantages of DVD-AUDIO audio when HD and Blu-Ray DVD are used as the carrier for pure audio encoding. The first is a larger data stream, which will be of great help to improve the MLP audio technology, the pure BD or hd dvd-Audio will increase from the original 9.6Mbps data volume to 18 mbps; the MLP technology also expands the number of Audio channels in the DVD-Audio from the previous six channels to eight channels to achieve more perfect and real Audio performance.
DTS-HD and Dolby's new generation of HD audio format, the realization of the true meaning of the 7.1 channel digital output, rather than on the existing 5.1 channel based on the decoding "simulation" to generate more channels. DTS-HD surround from encoding began to let the DVD disk have a really more sound surround mode, because when making a DVD film, it has been identified 13.1, even 32 loop mode in which, and with the DTS-HD's ultra-large data traffic characteristics, ensure that the sound information and sound quality have reached a higher level, the restored surround sound is closer to the real effect.
The downward compatibility of the DTS-HD is embodied in the design, is to adopt the core + expansion design method. The Core DTS Core (formerly DTS Encore) is a compatible part with a bit rate of 1.536 Mbps and 5.1 channels, which is lossy compression. The previous playback devices can recognize the core data streams and ignore all the extensions to achieve compatibility. If a new playing device is used, the core and extended parts can be recognized, and the two can be combined to achieve the highest sound quality.
DTS-HD is divided into several encoding and decoding formats based on different extended applications. DTS-HD can be encoded and decoded in three DTS formats-DTS-HD Master Audio, DTS-HD High Resolution Audio and DTS Digital Surround.
When all extensions are added, it is the highest DTS-HD Master Audio. DTS-HD Master Audio can process the Audio in the same bit as the original recording. The audio bit rate can reach 24.5 Mbps on BD and 18.0 Mbps on hd dvd. At this time, the 8-channel audio of 7.1 channels can reach 24 BIT/96 kHz, which is exactly the same as the original recording version. The extension plus is DTS-HD High Resolution. The DTS-HD High Resolution handles a 7.1-channel sound with no audible differences from the original sound.
The bit rate of dtshd high-resolution audio processing is BD 6 Mbps and hd dvd 3 Mbps. It can also reach 7.1-channel 24bit/96 kHz. Without expansion, DTS-HD Digital surround, which is the original DTS decoding format of home theater audio. If this format is retained, you can use the original playback device with DTS decoding capability to play BD and HD DVDs.
For the production of DTS-HD master audio, DTS company provides the latest audio coding tools-DTS-HD master audio suite, referred to as MAS. Mas not only supports DTS 5.1 music discs (I .e. DTS-CD), DVD-video, DTS Audio Encoding in DVD-audio. It also provides a complete set of solutions for the production of DTS-HD audio in the next generation of HD format CDS (BD and hd dvd), including audio codec, quality control and code stream management. Audio Encoding using MAS allows you to create surround audio with up to 7.1 channels, a sampling frequency of up to 192 kHz, and a transmission code stream of up to 24 .5mbps. This allows you to reproduce the original audio in bits.

Original flavor-LPCM

Lpcm (linear pulse code modulation, linear pulse Coding Modulation) is a technology for recording audio without compression. It extracts analog signals and converts them into digital signals in a continuous linear sampling mode, generally, the lpcm is a 16-bit/48 khz stereo signal, which is one of the standard audio specifications of the DVD and is basically not distorted.
In simple terms, the lpcm is the reproduction of uncompressed original audio, theoretically having the best sound quality. However, because no compression format is used, the data volume is very large and is generally used in CD and DVD. The same principle applies to CD, DVD, and even higher specifications. The difference lies in the difference between quantization accuracy and sampling frequency. The general CD type is 16bit/44.1 kHz, while the DVD type is various. The quantization accuracy can be divided into 16bit20bit and 24bit, and the sampling frequency can be divided into 48 khz and 96 kHz. In addition, the Dolby Surround Sound information can be entered in the lpcm signal for use by the Dolby targeting logic system.
That is to say, there is no need to decode the LPCM because there is no encoding at all. The record is actually a digital multi-channel linear signal. As long as it is transmitted through the transmission channel, it can be directly amplified after the DA (digital-analog) Conversion inside the power amplifier, therefore, the transmission path of the LPCM is the shortest.
However, we must reiterate that the LPCM is only the best Playback Method in theory. The sound quality of the recording depends on the quality of the recording. If it is made well, it is well deserved to be the best. If the quality is not high at the time of preparation, what we ultimately get is, it may not be as good as lossy compressed Audio, but it is more likely to be inferior to the Audio signal of Dolby TrueHD and DTSHD Master Audio that can accept post-Audio field processing (such as DSP sound field processing provided by power amplifier.

Conclusion

In the HD era, apart from Video Effects improvement, audio quality must also be improved simultaneously. From the next generation of encoding formats, it is not difficult to find that in the future, home cinemas will have at least 7.1 audio playback capabilities. Due to the introduction of more advanced encoding modes, at the same bit rate, we will enjoy higher quality audio.
In the new era of audio and video, signals, software, display devices, playing devices, and connecting devices are required. A perfect HD experience can be achieved only when shadows and sounds are truly combined.

 

 

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