Digital sound. How many myths revolve around this phrase. How many disputes arose between lovers of convenience and digital quality and adherents of the “lively airy” vinyl sound multiplied by the “warm tube” sound. In addition, there is a lot of debate among digital lovers: is 16x44.1 enough or is 24x192 needed? Which is better: multibit or delta-sigma? CDDA or SACD? PCM or DSD? In this article I will try in simple language outline the basics digital audio, and I will also dwell in more detail on the comparison of two types of analog signal encoding into digital: DSD and PCM.
First, let's answer the question, what is digital sound? How is it different from analog? In short, in mathematical language, analog sound signal- continuous function, digital audio signal - discrete function. What does it mean?
Analog signal
If we draw a graph of a sinusoid in our imagination (this is how a sound wave is most often depicted): then no matter how we magnify it, trying to consider all the details, we will always see a smooth smooth line: this is an analog sound signal (Fig. 1).
Rice. 1. Analog signal
Analog sound (recording) has many parameters with which you can evaluate its quality. Consider the three most important: frequency range, dynamic range, distortion.
SOUND STANDARDS
DVD technology allows you to record multi-channel audio, both in compressed form (Dolby Digital, DTS, MPEG) and uncompressed, in the form of linear and packet PCM. The more the sound is compressed, the worse its quality. Multichannel sound is designated as 2.0, 5.1, etc. - the first digit is the number of individual audio channels, the second indicates the presence of a low-frequency (subwoofer) track. Five-channel sound implementation involves 2 front speakers, 2 rear speakers, a center speaker and a subwoofer. With 6 and 7 channel sound, a central rear or a second central front or two side speakers are added. Many inexperienced users prefer Dolby Digital sound, but they do not know all its disadvantages.
The main formats for recording audio on DVDs are as follows:
Advanced Resolution (linear PCM and packed PCM)= applies only to recording MUSIC and only on DVD-AUDIO discs. This format provides the highest sound quality. Maximum resolution values = 24bit/192khz, however, equipment that supports such a high resolution is rare. The more common format is 24bit/96khz. Advanced Resolution comes in the following formats: 2.0; 4.0; 5.1
PCM (LPCM) (Pulse Code Modulation uncompressed)= linear pulse code modulated audio, just like a regular CD. On DVD programs usually recorded at a slightly better standard than CD = 16bit/48khz, but 20-bit recording is common. In very rare cases you can find 24bit/96khz - literally on single publications. This standard is used to record music programs, i.e. video clips and concerts, and for these programs it is the best. We have to deal with a lack of understanding among buyers who want to listen to music programs in Dolby Digital, but just listen on good PCM and Dolby equipment, and all the advantages of PCM become obvious even to the most deaf person. PCM comes only in 2.0, or STEREO, but if you want to hear surround sound, any receiver can easily decode this format into Dolby Surround Pro-Logic, however, the whole living essence of the music will die. Music should and should be listened to in uncompressed stereo format - this is the opinion of music lovers. PCM Stereo is the right choice for this.
DTS (Digital Theater System) is a surround sound recording system developed specifically for film distribution systems, later introduced into home video systems. The sound quality offered by this method is characterized by great dynamics and clarity. Audio compression is low - approximately 1:3, bit depth - 20bit, so DTS can compete with PCM in quality and is often used when publishing concert recordings on DVD. Some films are also released with a DTS track, although mostly in the original language. The DTS system provides the following number of channels: 2.0, 4.0, 5.0, 5.1, 6.1 and even 7.1. The last two standards are called DTS ES and DTS EX and require special decoders and additional amplification channels, although these two standards are compatible with conventional receivers with 5.1 sound implementation.
Dolby Digital is the most common and least good (or rather, most disgusting) sounding audio format in DVD technology. And this is not surprising, since the compression at maximum values reaches 1:11. True, the amount of this compression is variable and depends on the saturation of the audio stream, and with proper encoding, the shortcomings of compression can be somewhat leveled out. Nevertheless, for movies these shortcomings are almost invisible, but in music programs they are often very, very obvious, unfortunately. The method and quality of Dolby Digital encoding can be compared with recording in MP-3 format. And producers of music programs often follow the lead of the market, recording music in the popular popular Dolby Digital format, and not offering any alternative track in PCM or DTS. The Dolby Digital standard offers the following types of multichannel sound: 1.0; 2.0; 2.1; 4.0; 4.1; 5.0; 5.1; 6.1. THX certification of Dolby Digital involves making special changes in the time delays of the signal and in its frequency response. Naturally, it is used when recording film sound, but not music. Perhaps the only THX certified music release is the Rolling Stones "Live At The Max" concert, and even that, in fact, is a movie, since it was shot for screening in wide-film IMAX theaters.
Dolby Surround is an outdated surround sound system that allows you to get four components from a regular analog (not digital) stereo signal - right, left, center and rear channels, and it is also possible to connect a subwoofer. Additional channels are allocated by matrix decoding the out-of-phase signal from two stereo channels. This format is designated as 2.1, 3.1, 4.0 or 4.1
MPEG Multichannel is an outdated (rather stillborn) surround sound system offered by European disc manufacturers. It is practically no different from Dolby Digital; it was developed to avoid paying royalties to Dolby Labs. Currently, it is practically not found, except for rare French editions.
VIDEO STANDARDS
The DVD standard implies recording images with the aspect ratio adopted in television broadcasting, i.e. 3:4, or, in another way, 1.33. However, the vast majority of movies are shot in a different aspect ratio, namely 1.77; 1.85; 2.35, etc. That is, films are usually shot in widescreen. How can you fit a wide frame into the usual 1.33 format provided by the standard?
What happens to the image in this case is the most difficult to understand for beginners. Below on simple circuits We will explain to you how the image changes and what the user needs to know about it.
ILLUSTRATIONS ARE PREPARING:)))
ANAMORPHIC image is considered the highest QUALITY because it retains high resolution and allows, depending on the player settings, to watch the movie in both letterboxed and anamorphic form. If you have a regular, non-widescreen TV, then by specifying the TV type as 3:4 (normal) in the player settings, you will see a wide film as in picture 2, and by selecting the TV type as 16
:9 (wide), you will see an image like in picture 3. If you have a widescreen TV, then you can clearly see all the shortcomings of the letterbox, as in the illustration below:
ILLUSTRATIONS ARE PREPARING:)))
THE DEGREE OF ANAMORPHOSIS of a film image depends on the original film frame and ranges from 1.77 to 3.1; The most appropriate widescreen TV format is anamorphic at a ratio of 1.85. At higher ratios, narrow black bars appear at the top and bottom of the screen, but image quality is still consistently high. DVD collectors around the world prefer anamorphic editions. Top quality DVD pictures are produced on players with progressive scan capabilities that meet HDTV standards, i.e. high definition television.
What is PCM
Let's start with the fact that PCM (pulse code modulation) is initially older, the first mentions of its successful use date back to the middle of the last century and are associated, like many achievements of technical progress, with the defense industry, namely with Navy radars. As for household use, first of all it is a well-known CD with a sampling frequency of 44.1 kHz and a quantization level of 16 bits.
What is DSD
DSD (pulse density modulation) is a format developed by Sony and Philips at the end of the last century and intended for digital archiving of analog phonograms. The physical media of this format is SACD. In fact, these two formats have only one similarity - they are both digital, which for the user means the possibility of unlimited copying without loss. As for the difference, in relation to the field of graphic design, it is approximately the same as raster and Vector graphics. And if it’s even more artistic, it’s like cross stitch and watercolors. In both cases, a picture is obtained, but the method of its creation and, as a consequence, perception are completely different.
What is the difference?
PCM, even due to its age, is much more studied, has much better compatibility with a huge number of the most different devices, implies the possibility of editing (equalization, division into frequency bands, conversion). DSD is actually a closed format, you can record in it, you can play it, that’s all. However, it is by its nature much closer to the original analog signal.
What's better?
The first and most important conclusion is that from a technical point of view, the formats are very far from each other in terms of implementation methods, but are often practically indistinguishable in practical application, that is, in the sound of the final file. We are talking only about small differences in the nuances of music presentation. Therefore, all other things being equal, when choosing the next file to download and play, it is best to focus on the source material. If you are digitizing analogue, then DSD will probably be preferable and will retain more of the nuances of the original. If this is a remaster of a previously made digital recording in PCM, then it makes more sense for it to remain in this domain.
When it comes to high definition audio played from a Blu-ray player on a computer, many tend to think that the presence of an HDMI interface on the motherboard or video card automatically allows you to play high definition audio formats such as Dolby on your TV and home theater. Digital Plus, DTS-HD High Resolution, Dolby TrueHD and DTS-HD Master Audio. However, with the exception of a few interesting opportunities, in most cases this is absolutely not the case. Even relatively new ones equipped with a high-end HDMI interface motherboards, video cards and sound cards may not be able to handle such large streams of audio data on their own. It all ultimately comes down to what type of input signal they can accept and what kind of signal they can output.
In this review, we will look at all HD audio formats, their bitrate (stream) and delivery requirements to the playback medium. In Part 2, we'll continue to explore how digital audio streams may (or may not) be handled in typical PC components. After reading both articles, you should come away with a deep understanding of why so many home theater system users use multiple analog cables (three for 5.1-channel audio and four for 7.1-channel audio) instead of HDMI to get multi-channel audio to where they need to go. . We'll also cover some alternative solutions to converting digital to analog in a computer rather than a receiver or preamp, which is often the most accessible option for achieving optimal quality HD audio. Finally, you may understand why you should wait a little longer to buy a Blu-ray player for your home theater system; this will allow you to take advantage of some new benefits that should be available before the end of 2008, but are not quite ready yet (at least not ready at the time of this writing).
In the first part we will cover the following points.
- Blu-ray audio formats: Pulse Code Modulation (also called PCM, or sometimes LPCM from Linear PCM, supported by most audio devices), three types of Dolby (Dolby Digital, Dolby Digital Plus and Dolby TrueHD) and DTS (DTS, DTS-HD High Resolution and DTS-HD Master Audio).
- The bitrate (or stream) associated with each format, as well as the number of channels, sampling rates, and bit depths used to encode the formats.
- Can the SPDIF connector provide the required stream for each format, and what types of HDMI interfaces does each format work with?
In Part 2, we'll look at PC software codecs to find out what formats they work with, as well as the types of interfaces that HDMI-equipped motherboards, video cards, and sound cards can support. And since new chipsets and interfaces have recently become available (or will be available relatively soon), we'll also explain how new and upcoming Hardware can provide more simple solutions for high-definition audio for PC, which is on this moment is in a deplorable state.
High definition audio formats (HD audio)
Blu-ray discs can contain movie soundtracks in one of the following formats.
- PCM (Linear PCM, or LPCM);
- Dolby Digital;
- Dolby Digital Plus;
- DTS-HD High Resolution;
- Dolby TrueHD;
- DTS-HD Master Audio.
Before we move on to a detailed examination of the above formats, we note that Dolby technologies originated in the company Dolby Laboratories renowned provider of professional, semi-pro and consumer noise-canceling and multi-channel surround sound technologies. The DTS format (also called Digital Theater Systems) in turn comes from DTS, Inc.- also a well-known supplier of digital audio technologies, competing with Dolby Labs technologies.
PCM (Linear PCM or LPCM)
PCM stands for pulse code modulation and provides a digital representation of an analog signal, which is sampled (digitized) at regular intervals (with a specified frequency in hertz) and presented in binary form (with a specified precision - bit depth). In addition to using PCM for digital audio in computers and audio CDs, this format also used in some digital telephone systems and in a number of digital video formats. In PCM format, audio amplitude values are represented using different numbers of bits (depth); The audio track is typically digitized at 12 to 24 bits, but most studio encoding of PCM audio for Blu-ray disc recording uses 16 bits.
A PCM audio track can be an exact copy of the studio original, encoded onto disc without compression, as long as its bit depth is the same as the original. If the bit depth is reduced (as is often the case to save audio space on disk), this can result in downsampling: for example, using 16 bits instead of 24 bits. In technical terms, downsampling is not the same as compression, although it does reduce the fidelity of the resulting audio.
All Blu-ray players must support PCM Audio to comply with the Blu-ray specification, however not all Blu-ray discs include this format. Many movie database sites provide detailed information about Blu-ray discs, especially on the website Cinema Squid You can find a table ("The Audiophile") of the audio characteristics of various Blu-ray discs, where they are given a score on a scale from 0 to 100. Typical characteristics include the audio codec used (for example, Audio Codec: LPCM 5.1 - the only PCM presented format), the number of channels that a given codec provides on the disc (for LPCM you will find values of 2.0 for stereo, 5.1, and also rarely seen from time to time 6.1 and 7.1), audio fidelity (Audio Fidelity: usually 48 kHz/24 bit or 48 kHz/16-bit) as well as the stream (the highest value we could find was 13,824 kbps for the unusual 96-kHz/24-bit audio; but the most typical stream was 6,912 and 4,608 kbps for 48 -kHz/24-bit and 48-kHz/16-bit values, respectively).
The table at the end of our article provides information on Blu-ray audio formats: sound circuits(number of channels), support SPDIF and HDMI for PCM format. The good news about the PCM format is that if your computer can output this data via HDMI to your receiver, and your receiver supports PCM data streams, then you can probably decode 5.1 or 7.1 HD audio on your computer and output it to a home theater in PCM without losing quality. Any type of HDMI interface is suitable for PCM or LPCM: from HDMI 1.0 up to HDMI 1.3a.
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What is "video" high resolution", many understand; but what's the point of talking about HD audio at the recreation center? This term refers to multi-channel audio formats recorded on Blu-ray discs. Various methods are used to store digital audio, but their purpose is the same: best sound for your home theater.
Best? How much better?
On order. HD audio dramatically improves quality, and you don't need to be an expert to hear it. Every aspect of the sound improves - from dynamic range to realism. According to Dolby sales manager Andy Dowell, "You hear exactly what the mixing engineer heard during the mix - down to the beat." Anthony Wilkins, director of marketing at DTS, says: “When we discussed data compression for DVD audio, the correct term would have been 'trimming' because part of the original signal was irreversibly lost during the encoding process. This does not happen with HD audio codecs for Blu-ray; the result is identical to the original."
Identical to the original? Fully?
Exactly. Today, original movie audio tracks are recorded in uncompressed PCM format at 24-bit/48 kHz (better than CD). After mixing, the soundtrack is highly compressed for playback in the cinema or at home; it's similar to making an MP3 from a CD. In the Dolby Digital system, most often used for DVD creation, the bitrate corresponds to a good MP3 file - from 384 to 448 kbps. Compression has always been undesirable, but it was necessary in order to be able to “squeeze” the multi-channel sound of an entire film onto a limited reel or disk. However, a Blu-ray disc has a capacity of up to 50 GB, so there is no need for compression. Such a disc is capable of storing a complete soundtrack in PCM 7.1 format with 24 bit/48 kHz parameters; even a single-layer 25GB disc can easily accommodate an uncompressed PCM 5.1 audio track.
Why then doesn't every disc contain PCM audio?
It takes up quite a bit of space, especially on less expensive 25GB drives. To leave room for extras, foreign language tracks, commentary and the actual video component of the film, studios follow one of two approaches. One is to downscale 24-bit PCM audio to 16-bit/48kHz. However, it is more popular to use two lossless audio recording systems - DTS-HD Master Audio and Dolby TrueHD.
What does "no loss of quality" mean?
These systems are similar to file archivers: they pack 24-bit/48 kHz PCM into a smaller amount of memory. Playback requires "unzipping" the recorded file back into PCM; Both Blu-ray players and most AV receivers can do this. Dolby TrueHD technology produces 24-bit/48 kHz PCM audio but requires nearly half the storage space. In theory it should be identical to the original; Dolby and DTS say so. That's why these two technologies are so popular in Hollywood: they provide very high quality sound, but require more modest amounts of disk space compared to PCM. This reduces the cost of the disk (allowing you to limit yourself to 25 GB of media) and leaves more space for additional materials.
What the numbers say
For storage audio track A two-hour movie in PCM 5.1 (24 bit/48 kHz) requires 6.2 GB of memory. Dolby TrueHD reduces this figure to 3 GB; The more different audio channels a film has and the longer it is, the more useful the compression. As for comparing the two systems, DTS-HD Master Audio has a higher bitrate than Dolby TrueHD (24.5 Mbps and 18 Mbps), but in practice these values are almost never achieved. Some discs have tracks in both formats. Overall, both of them are quite good.
Three Major HD Audio Formats
- PCM uncompressed
PROS: Fantastic quality, like 3:10 to Yuma. Does not require “unzipping”; also available for older Blu-ray players or AV receivers.
CONS: Takes up a lot of space: Yuma in 7.1 format requires more than 8 GB.
- Dolby TrueHD
PROS: Amazing sound quality; takes up much less disk space than PCM. The Dark Knight soundtrack in TrueHD is one of the most amazing.
CONS: In theory, a bitrate of 18 Mbps gives slightly less than 24.5 of DTS-HD MA.
- DTS-HD Master Audio
PROS: The most common lossless codec on Blu-ray discs; sounds wonderful - the Avatar soundtrack proves it.
CONS: Some argue that it is actually better than Dolby TrueHD; We're not sure about that.
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