The structure of SACD is roughly similar to that of DVD, with single and double playing surfaces and single and double information layers. At present, most SA CD disks on the market adopt single-sided and double-layer structure. One layer is a 0.6mm substrate, which stores the signals in the traditional CD format of 16bits and is compatible with CD, and the other layer is a high-density translucent layer of the 0.6mm substrate, which stores the signals in SACD format, and then the two substrates are bonded together like DVD discs. This kind of CD can be played on ordinary CD player or SACD player. Of course, their sound quality is different.
The technical index of SACD is far superior to that of CD, but it is similar to that of DVD-Audio.
The core technology of SACD is DSD (Direct Stream Digital), which is essentially different from the multi-bit recording principle of CD and DVD-Audio.
Technical points of drainage services department
The technology of DSD is simply to sample the signal at 2.8224MHz and output a signal stream of 1bit after multi-stage delta-sigma modulation.
Multi-stage (such as 7th-order) delta-sigma modulator, which uses negative feedback to compare the signal with the waveform sampled last time (differential operation), and outputs "1" if it is greater than it, and "0" if it is less than it. The adder accumulates waveforms in the sampling period to form the next comparison waveform. Δ and ∑ respectively represent the sum of differences. It can be seen that 1 bit signal stream is a relative value, while the quantized value recorded by traditional PCM is an absolute value.
It is a schematic diagram of 1 bit data flow after sine wave is modulated by multi-order Δ-σ. The figure shows that in the positive half cycle, the greater the amplitude, the more "1" appears; In the negative half cycle, the greater the amplitude, the more "0" appears. This picture reminds us of the sound waves transmitted by the loudspeaker in the air: in the first half of the week, the paper basin is pushed out to compress the air in front of the loudspeaker and increase the air density. The greater the amplitude, the greater the density; In the negative half cycle, the paper basin is pulled back, which reduces the air density. The greater the amplitude, the lower the density. It can be seen that the 1bit signal stream actually reflects the sound density formed in the air after the original analog signal acts on the speaker! At present, some companies have been developing digital power amplifiers and digital speakers, hoping to provide 1 bit binary data directly to digital speakers after being amplified by digital power amplifiers. Digital loudspeaker is not only a simple low-pass filter, but also a transducer that converts electric energy into acoustic energy, which not only simplifies the structure, but also improves the playback performance. I believe that in the near future, we will see the practical application of this digital device.
Compared with the traditional PCM signal, the modulation process of 1bit signal stream is simpler, with high precision, low cost and simpler demodulation process. Theoretically, the audio analog signal can be successfully restored only by an RC integrating circuit at the playback end. At the same time, some inherent distortions of PCM are fundamentally eliminated, and audio signals are highly restored. The sampling frequency of DSD system is 2.8224MHz, which is 64 times that of traditional CD (44. 1kHz), and the total information capacity is 4 times that of traditional CD. Theoretically, the frequency response range can be extended to 0Hz-400kHz, which greatly exceeds the limit of traditional CD 20k Hz. And the oversampling frequency of 64 times that of CD can make the quantization noise in the auditory range completely distributed outside the auditory range of human ears. Moreover, the so-called "noise shaping circuit" is developed in DSD technology, which can further transfer the noise in the audible frequency band (0 ~ 20kHz) to the super audio frequency range above 20kHz, thus making the signal-to-noise ratio of SACD as high as 120dB.
Comparison between SACD and DVD-Audio
Although their principles and circuits are different, their sound quality is much better than that of traditional CDs. As far as technical indicators are concerned, SACD is comparable to DVD-Audio. Therefore, the dispute between the two has not yet been unified. But as far as the current situation is concerned, SACD has always maintained a leading position.
First of all, SACD is one step ahead of DVD-Audio in hardware supply. As early as two or three years ago, Sony had a flagship SCD- 1 that caused a sensation in the industry, followed by SCD-777SE, SCD-555, SCD-XB940, and even DVP-S9000ES and MANNT900. Philips' SACD 1000, Japan's famous Hi-Fi products' DP-100/DC-1splitter, and others, such as Japan's Joan, Aiwa and First Audio, are too numerous to mention. So far, the DVD-Audio lineup has only a few varieties of Panasonic, Shengli, Tianlong and other companies. Recently, however, DVD audio is catching up.
Secondly, SACD was the first country to provide software. Up to now, more than 300 kinds of SACD records have been published, and nearly 100 kinds can be seen in China. On the one hand, Sony and Philips rely on their own record companies to continuously publish SACD records to show their support. On the other hand, we persuaded Telarc, DMP, Nassau, DI GITAL and other fever record companies to join SACD Chen Ying, and constantly introduced SACD software, which left a deep impression on consumers. However, DVD-Audio was unlucky, and the anti-piracy password was cracked in the cradle by computer hackers, which greatly delayed the launch schedule of DVD-Audio records, which is also the main reason why many record companies suffering from piracy temporarily did not consider supporting the DVD-Audio camp.
Grade: SACD has positioned itself at the high-end level from the beginning. Sony's first flagship SCD- 1 is extremely feverish. Both the internal materials and the whole machine technology are designed in strict accordance with the specifications of Hi-end record player, and the low-end models to be launched in the future are also designed and manufactured in strict accordance with the concept of heavy and stable materials. It is welcomed by most hi-fi enthusiasts. In the struggle with SACD, DVD-Audio camp has always regarded DVD-Audio as a cheap and effective function, which is attached to popular DVD players for publicity, giving people the feeling that it is a staple food. In addition, DVD-Audio has many functions, but it is not exclusive. The body is slim and the material is ordinary, which is not good-looking in the eyes of audio enthusiasts, thus losing to SACD in terms of grade.
Sound quality: Due to SACD's own positioning and the technical simplicity and advantages of 1 bit quantized DSD direct data stream, most experienced audio enthusiasts feel that SACD is slightly superior in sound quality after hearing it with their own ears. So many friends in the audio industry think that if a home theater is compatible with Hi-Fi, DVD-Audio should be the first choice. However, SACD is your ideal choice for friends who mainly play high-fidelity music, especially those who pursue true and pure sound quality and timbre.
Introduction to xrcd
Xrcd adopts K2 interface developed by Japanese JVC company, including mastering equipment, manufacturing technology, hardware and theory. By inventing this technology, the original master clock system is used to control the time base of each link in optical disc production, which greatly reduces the jitter distortion coefficient of optical disc production and the group difference coefficient of glass master mold, and correspondingly improves the plate-making accuracy, thus greatly ensuring the fidelity in optical disc production.
Xrcd can be said to be a perfect 16 bit, and it can present the highest sound effect of cd on any record player without any additional equipment. On the same sound system, xrcd is obviously superior to the original cd in transparency, smooth extension of high frequency, three-dimensional sense and smooth texture of beads. What a transparent voice, clean background, musical instruments and voices without any anger and burr. This is the first time to listen to XRCD. The original CD is like a mist between the listener and the player. Xrcd is like a gust of wind blowing away the light smoke, and everything is clear in front of you.
Introduction to xrcd2
Xrcd2 is an upgraded version of Xrcd.
Xrcd2 has taken a big step towards the goal of perfect digital audio. It is a representative technical achievement of JVC's deliberate pursuit of reproducing the original sound for many years. Xrcd2 is a recording product developed after in-depth study of related equipment and theories in the process of master art processing and industrial processing. She provides a better version of xrcd series for the audience who are looking for high-level sound quality. At the same time, like other products in the xrcd family, it does not need to use a special decoder and a special cd player.
The usual optical disc processing procedure is to arrange the master disc and send it to the processing factory for tabletting with U-matic 1630 tape or PMCD or DDP tape. From then on, performers, producers, directors and sound engineers can only pray that the products-CDs-will not change much with their carefully created works. There is no sound judgment benchmark between the recording studio and the production and processing factory. Even if the digital series is correct, it may not guarantee the highest sound quality reproduction. In addition, the production process of CD is composed of a variety of equipment and technologies, so its sound quality is also affected by various equipment conditions. This means that in order to faithfully reproduce the sound recorded on the original master, we must seriously pursue every tiny link from the tuning of the CD master to the production and processing. Therefore, it can not only meet the simple and high index of the existing detection data. Therefore, we should not only rely on simple test data, but also use long-term auditory experience to judge the best equipment with the best auditory effect. This effort even includes various test combinations from installation connection mode, AC power supply system, clock accuracy, recording format, handover system to CD material, and the result is xrcd2. So far, she has described the original sound more clearly than any CD, thus successfully providing a CD with better sound quality.
The processing of xrcd2 starts from the processing of the host. The analog signal is first made by a special mixer, and then converted into a digital signal by a 20-bit K2 A/D converter made by JVC Company. Then this 20-bit digital signal is output from the SDIF-2 interface through the newly developed digital K2 and recorded on the magneto-optical disk (MO). In this process, digital K2 is used to block the influence of digital part on analog part, thus realizing high-purity analog-to-digital conversion. In addition, in the processing procedure of xrcd2, a magneto-optical disc with stability and recording capacity greater than 20 bits is used as an audio recording carrier to be sent to the production procedure.
I got a 20-bit PCM-9000 magneto-optical disc from JVC Yokohama Factory, and played it again through the number K2. In this playback stage, the "Gita" noise parasitic in the digital signal is eliminated. Next, K2 super encoder converts the 20-bit signal into a 20-bit dominant 16-bit signal, which is encoded by EFM and sent to K2 laser. Here, the EFM signal is played back before being sent to the laser disc recorder. In the final stage, the residual transient "Gita" noise in the data stream is removed.
Through the above process from the master to the production process, the highest sound quality of the original master is transmitted to the CD. Fully take care of the details of the original sound, so as to reproduce the delicate performance of the performer, and reproduce this sound without distortion during recording, so that the audience can fully understand the performance intentions of the performer, producer, director and sound engineer. This is xrcd2.
Xrcd technology has been well received by the industry, and the latest version of xrcd2 products has strengthened the advantages of xrcd series in faithfully reproducing the original sound. In order to maintain the advantages of xrcd brand, JVC company has strict requirements on the quality selection of master tapes, and various processes such as master tape reproduction, master tape production and tabletting. In addition, due to technical secrecy and other reasons, JVC company strictly stipulates that it can only process and produce in its local designated studios and factories. Because of these characteristics, even if illegal copying is carried out in such a strict way as digital to digital engraving master, the advantages of xrcd will not be obvious without using xrcd technology in processing. So xrcd is also called "cd that can't be pirated".
What is HDCD?
HDCD is the abbreviation of high definition compatible number. It adopts a new recording technology. When the analog audio signal on the master tape is sent to the HDCD encoder, it will be encoded into a digital signal, the resolution of which exceeds the traditional CD standard of 44. 1KHz and 16bit, and the generated signal will exceed the capacity of ordinary CD.
CD status quo
12cm CD has been published for more than ten years. Because of its unique advantages such as small size, easy storage, wide frequency response, high signal-to-noise ratio and large dynamic range, it is still the main audio source of Hi-Fi equipment. With the improvement of people's appreciation level, the inherent defects of CD sound source are increasingly prominent. Compared with traditional LP records, the sound played by CD always has a little stiff feeling, with few details and a lack of presence. If the sound quality of VCD, which has been rising in recent years, is included, many friends and experts will feel sorry for it.
For this inherent defect of CD, we have to start from the red book specification formulated by CD in that year.
Limited by the hardware and software of microprocessor technology at that time, the red book standard of CD DA laser turntable published in February 1982 made the following provisions: turntable diameter 120mm, disk speed 1.2m/s, modulation mode EFM, error correction CIRC, data rate of 0.6Mbps, and data volume of 0.7GB.
Due to the limitation of CD capacity and chip technology at that time, 16 bit operation was adopted for quantization, and its dynamic range d was d = 20lg2+1.76 [db] = 98db (n =16), which is the theoretical dynamic range of CD.
The frequency response of 20kHz, dynamic range of 97dB and unpredictable jitter make the laser turntable shine in the field of digital audio, and soon it will become Hi. The important sound source of Fi sound reproduction equipment makes people abandon tapes and bakelite records without hesitation. However, with the further development and discussion of digital audio. The defects of this 44. 1 kHz/ 16bit recording format are increasingly prominent.
First of all, the sampling rate of 44. 1kHz is the first factor that affects the sound quality and timbre. 44. The sampling rate of1kHz can completely reproduce a 20kHz sine wave, but it is difficult to completely reproduce a 7kHz non-sinusoidal signal. This is because non-sinusoidal signals can be decomposed into fundamental waves and second and third harmonics. Although the fundamental wave can be reproduced, more than three harmonics may be lost or distorted after D/A conversion, which makes the final waveform different from the original information and changes the timbre.
Limited by the knowledge and conditions at that time, the data information recording format of CD is defined as 16bit, which can theoretically reach a dynamic range of 98dB. In fact, in order to avoid strong clipping, a safety margin is left, and 16bit cannot be fully used. In addition, the loss from recording and encoding to decoding makes it difficult to break through the dynamic range of 96dB, which is very important for the performance of classical percussion (1655). This is a unique distortion of digital audio-subtraction distortion.
Because the original analog information is infinite and constantly changing. The information on the CD is recorded by dividing the original information into 65536 stages. In order to perfect the information, 16-bit CD recording must round the sound between processing stages and add it to the previous stage or the next stage. In this way, even if the information contained in the CD can be completely restored, there are errors compared with the original sound.
If the quantization accuracy is high, the original analog information will be more real and more detailed. Comparing the pictures of 16-bit game consoles and 32-bit game consoles, it is easy to draw a conclusion. The quantization of low bits makes the quantized error greater than that of high bits, and the quantized error (quantization noise) makes the hearing feel stinging and turbid, especially when the signal is small, and these harmonic components that cannot be found in the original signal constitute additional distortion.
As a special case of digital audio, the sound quality of VCD is the result of typical digital operation. Compared with ordinary CD records, it feels more empty, lacking details and layering, and the high-pitched sharpness is more prominent. This is because VCD can play back image and sound information on a 12cm optical disc, and it ignores the information that people are not easy to perceive by using the masking effect of human ears, and compresses and reorganizes a lot of data. The process is a large-scale subtraction operation, and the final result is similar but lacking in spirit.
If digital processing with high bit rate and high sampling rate is adopted, the sound quality can be greatly improved. In fact, many record companies have already made the master tapes with the sampling rate of 96kHz and 20 ~ 24bitCD in advance. However, when making CD records, due to the current CD specifications, they had to re-encode to conform to the format of 16bit/44. 1kHz, so everything we can see is marked with.
If we want to change the present situation of optical disc, we must first subvert the existing optical disc format and adopt high sampling and high bit recording format and playback equipment, which will undoubtedly increase the information capacity and transmission speed. The current CD player is incompetent, but the advent of DVD can solve this problem. However, the recording format of high-quality audio CD has not yet been determined, and once it is determined, it means that CD turntables, DAC, LD and VCD players in the market for more than ten years will all become toys without it, and even CD players with a price of 10,000 yuan will be doomed.
Another way to solve the problem is to improve the advanced CD in order to make a breakthrough under the current system, just like the transition from black-and-white TV to color TV. HDCD technology is a successful and mature model of this scheme.
Introduction to HDCD
In order to improve the defects of the existing CD recording format, make it highly compatible, and make a breakthrough in sound quality, Pacific Micro Sound Company of the United States introduced a new technology for recording and playing HDCD, and obtained patent protection. Its full English name is High Definition Compatible Digital, which is translated into a high-resolution CD. HDCD-encoded optical discs have high compatibility with ordinary optical discs. When it is played on an ordinary CD player, the advantages of HDCD coding and recording technology can be reflected. If you play it on a CD player with HDCD decoding function, you can fully appreciate the unique charm of all published HDCD information: the sound quality is clear and delicate, the dynamic range is wide, the signal-to-noise ratio is extremely high, and the timbre is more natural and realistic.
Coding and manufacturing of HDCD
In view of the limitations and shortcomings of the traditional CD recording format, Keith O Johnson, two founders of HDCD in PM company, and Michael W.pflaumer, a computer expert, have discovered and confirmed several key factors affecting the sound quality of CD during their years of sound production, and put forward practical solutions.
HDCD technology pays attention to the integrity and accuracy of the recorded signal in the early recording production, and samples the analog signal at a sampling frequency of 88. 1kHz, which is twice the conventional sampling frequency, so as to maximize the high-frequency response and reduce the defect distortion. The high sampling rate also leaves enough space for HDCD encoding operation.
With 24-bit quantization, the sampling value is 16772 16, which is 256 times higher than that of 16-bit system. The high-level processing technology can improve the processing accuracy, reduce the quantization error, and improve the dynamic range to 120dB.
In the process of analog-to-digital signal conversion, HDCD technology attaches great importance to conversion accuracy and minimizes crosstalk and processing stability. The index it can achieve is one millionth of the conversion accuracy and distortion component.
This high-precision, broadband digital signal forms the basis of HDCD coding and manufacturing, and its data information is very huge. It can't adapt to the traditional CD pulse code modulation format. If you want to play compatible on an ordinary CD player, you need to encode it through special operations.
Using high sampling and high bit technology to record CD has been generally recognized and widely used, but it needs to be reminded that the essence of 20-bit and 24-bit CD laser discs available in the market at present should be the number of bits used in the recording process. Due to the limitation of the standard format of 44. 1kHz/ 16bit formulated by the CD "Red Book", these high-information master tapes need to be recalculated when recording CD records. So the specifications we can read on the CD player are still 16bit/44. 1kHz. Due to the different methods used by record companies in the conversion process, the sound quality of different versions of CDs we can hear now is indeed different, but one thing is certain: the sound quality of CDs made by high-bit and high-sampling technology is far better than that of 16 bit/44.6438+0 kHz recording.
So how does HDCD technology make HD records compatible with ordinary CDs?
Sampling frequency conversion. Firstly, the sampling data of 88. 1kHz is dynamically converted, which is a major feature of HDCD technology. It uses multiple data interpolation filters for dynamic control through an analysis system, analyzes the signal bandwidth, peak energy and high-frequency information in real time, and accurately controls the pass-through characteristics of the filters with high-resolution signals. Therefore, even if it changes to the final sampling rate of 44. 1kHz, its bandwidth changes little from 16 kHz to 22 kHz. The system has a sampling rate of more than 44. 1kHz, which can reflect every subtle change of sound.
Analysis of amplitude. Another feature of HDCD technology is that the amplitude is effectively controlled. The signal transmitted by the decimation filter is a 24-bit /44. 1kHz signal. In order to adapt to this kind of signal, the encoder performs accurate amplitude analysis and gain control at this stage, quantizes and edits it into 20 bits, and then assigns it to 16 bit format for operation.
The acoustics of nature vary widely. Sudden sound pressure will cause instantaneous overload of recording equipment and peak clipping. In the process of analog tape recording, level compression is used to avoid complete distortion of the tape. For digital recording system, overload will lead to unnecessary quantization error (data fragmentation) and affect the sound quality. Therefore, the common analog-to-digital converter device has an absolute maximum recording level (0dB) to ensure that the peak value will not be clipped. HDCD adopts a unique amplitude coding technology, which can obtain more capacity of 1 bit (equivalent to ++6dB) than traditional digital recording to process large dynamic signals. Due to the use of digital operation processing, this extended information can control the decoder recovery of playback equipment with accurate and stable characteristics. Coupled with the unique digital processing "foresight" ability, the system can restore the gain immediately before the start of large signals and provide more information capacity to avoid instantaneous signal overload.
For this one-bit information expansion, when to operate is constrained by the implicit control code of HDCD (mentioned later). For ordinary CD playback, the information remains the same, but when playing with HDCD decoder, the information can be accurately expanded under the control of implicit code to achieve the purpose of large dynamic playback.
Jitter (high frequency disturbance technology). Using high-frequency perturbation technology can improve the resolution of quantized signal, improve the nonlinear transformation characteristics of quantizer, reduce the harmonic distortion of low-level signal, and possibly reproduce signals below quantization difference. However, if it is added improperly, the disturbance will become real additional noise. HD CD technology adopts improved high-frequency disturbance technology, which has richer music details and lower noise.
HDCD implicit control code. For the last quantization operation part of HDCD, in order to accurately control the excessive information recorded by HDCD coding to be accurately played on the decoder, the relevant control code is specially set and inserted into the least significant LSB bit of the data recording block segment. If you play the code with an ordinary CD player, there will be hints and you will not be excited. Because it is located in a specific position, it only occupies the LSB of 1% ~ 5%, which has a weak influence on the sound quality of CD and is inaudible. When playing with HDCD decoder, the system can accurately capture the hidden code, and use it to activate the information of the main data channel, so as to expand the information, and the information output is several times that of the ordinary CD format. After DA conversion, an analog audio signal with large dynamics, rich details and high signal-to-noise ratio can be obtained.
In order to avoid error code operation, HDCD adopts dual-code synchronous timers in the main channel and the secondary channel, so that it will not be misaligned with the main information in the block segment. Only when the hidden code echoes the main related code, the main channel selection data is valid, otherwise the decoding operation is cancelled.
After the analog audio signal is low-pass filtered by the buffer, the analog-to-digital conversion is carried out first, and the ADC is controlled in real time by the high-frequency disturbance signal, and the 88. 1kHz, 24-bit data stream is generated by quantization. The data stream flow to that main channel and the auxiliary channel, the main channel information is delayed and store, and a component of the auxiliary channel information is analyzed before the main channel to generate a control signal, which dynamically controls the digital filter to perform sample rate conversion, amplitude code and gain control. Finally, the information that is easy to be missed after analysis, filtering and data reformatting is separated by the microprocessor (these information may involve timbre, sound field and subtle sound), and the hidden code and the control code are inserted into the LSB bit of the audio data of the main channel, and then quantized into the standard CD format of 16bit/44. 1kHz through high-frequency disturbance processing, thus completing the whole set of HDCD coding process.
Decoding process of HDCD and PMD 100
The decoding operation of HDCD is the reverse of the encoding process. The purpose of the design is to replace the digital filter of DAC with the decoding ASIC of HDCD, so as to complete the dual functions of HDCD information decoding and oversampling digital filtering.
The decoder first detects whether the LSB bits in the data stream carry HDCD hidden codes, and if so, activates the audio data information of the main channel for expansion according to the continuous instructions of the hidden codes, and resumes the compression of the data information during the encoding process. Because of the control of the hidden code, the peak value can be accurately extended in time, and the gain can be appropriately reduced for the information below the average level, so the HDCD method can obtain higher definition than the conventional large dynamic small signal.
As the only decoding chip of HDCD, PMD 100 produced by American PMI company needs authorization. This is a large scale integrated circuit with 28-pin DIP package.
When the input data received by PMD 100 is in HDCD encoding mode, it will automatically switch to HDCD decoding format, and the output current of PMD 100 will drive LED as status indicator.
When the signal is not HDCD, the information data is received for traditional oversampling digital filtering, so the device has dual characteristics. When it is used as a common digital filter in CD format, the characteristics of the device are also quite excellent. From 0 to 0~20kHz, the passband ripple is less than 0.000 1dB, and the stopband attenuation is >: 120dB.
Other features of the equipment are:
Digital filtering with 2, 4 and 8 times oversampling
Acceptable 24-bit input data and the same precision processing.
It can be sampled at any input frequency of 32~ 55kHz.
Output different data formats of 16, 18, 20 and 24bit.
With digital de-emphasis function
Digital volume control can be performed in steps of 0. 188dB.
The clock frequency is 256fs or 384fs.
Use soft and hard pressing methods.
Two control modes are provided: hardware setting and program mode.
Eight different types of high-frequency disturbance modes are provided to adapt to different types of DAC.
A constant output clock is provided for the DAC, so that even if the input data and the main pulse are lost, the DAC output can be guaranteed to be free from offset and pulse generation.
The pin arrangement of the decoding chip PMD 100 is similar to some top digital filters, such as SM5842, SM5803, DF 1700 and so on. Therefore, on the DAC or CD player with the above filter, the ordinary CD player or DAC can become a processor with HDCD decoding function with a little modification.
Unconsciously, CDs (compact discs) have been available for more than ten years, and countless music lovers and enthusiasts have collected hundreds or even thousands of CDs like the author. However, at the beginning of the new century, we have to face the reality that the variation of CD (or enhanced CD), SACD and DVD-Audio has gradually formed a situation of three heroes competing for hegemony. As consumers, where should we go? This article will unveil their mystery with you.