What is HDCD?
HDCD is the abbreviation of High DefiniTIon CompaTIble Digital, which uses a new recording technology to exceed the traditional CD format when sending analog audio signals on the master tape to the HDCD encoder. KHz, 16bit high resolution is programmed into a digital signal, and the signal generated at this time will be more than that of a normal CD.
Problems with CD specifications
The 12cm CD laser has been around for more than a decade. Because of its many unique advantages such as: small size, easy to save, wide frequency response, high signal to noise ratio, and large dynamic range, it is still the main source of HiFi equipment. As people's appreciation increases, the inherent defects of CD sources are becoming increasingly prominent. Compared with the traditional LP record, the sound played by the CD always has a little hard feeling, the details are few, and the sense of presence is lacking.
For the inherent flaws of the CD, it is necessary to start with the specifications of the Red Book that the CD made in that year.
Limited to the limitations of micro-processing technology hardware and software at that time, the CD DA laser disc red book standard released in February 1982 was as follows: disc diameter 120mm, disc speed 1.2m/s, modulation mode EFM, error correction CIRC, data rate 0.6 Mbps, the amount of data is 0.7GB. If you want to record the changed analog audio signal on this CD, you must first sample the analog signal. The condition for reproducing the signal waveform is based on Shannon's theorem: set the signal bandwidth to Bw, and the sampling frequency to fs, if Bw< With the condition of =fs/2, the original waveform can be completely reproduced. Based on the results of the study that the human ear can hear the highest frequency of 20 kHz, the sampling frequency of the CD is 44.1 kHz, and the sampled values ​​are discretely quantized (ie, quantized) with respect to the amplitude, and a series of After the pulse train, plus the CIRC error correction code, synchronization signal and address information, the data information obtained by the EFM format modulation can be poured onto the CD record.
Due to the limitation of the capacity of the disc and the chip technology at that time, the quantization uses 16-bit operation, and its dynamic range D can be expressed as D=20lg2+1.76[dB]=98dB(n=16), which is the theoretical dynamic range of the CD.
The frequency response of 20kHz, the dynamic range of 97dB and the low unmeasurable jitter make the laser discs shine in the digital audio field. It becomes an important source of HiFi sound equipment in a short period of time, so that people Do not hesitate to abandon tape and bakelite records. However, with the further deepening and discussion of digital audio. This 44.1 kHz/16-bit recording format has become increasingly prominent.
First, the 44.1 kHz sampling rate is the first factor affecting sound quality and tone. The 44.1 kHz sampling can completely reproduce a 20 kHz sine wave, but it is difficult to completely reproduce a 7 kHz non-sinusoidal signal. This is because a non-sinusoidal signal can decompose a fundamental wave plus a second harmonic... harmonic composition. Although the fundamental wave can be reproduced, more than three harmonics may be lost or distorted after the D/A conversion, so that the resulting waveform will be different from the original information, resulting in a change in the timbre.
At that time, the understanding and condition constraints, the data record recording format of the laser disc was defined as 16bit, and the theoretical dynamic range that can be achieved was 98dB. In fact, there is a safety margin to avoid strong clipping, and it is not enough to use 16bit. Coupled with the loss of the recording code to the decoding process, the dynamic range is difficult to break through 96dB, which is obviously not enough for the performance of classical percussion (118dB). This is a kind of distortion-defective distortion (SubtracTIve distorTIons) that people find.
Because the original analog information is infinitely continuous. The information on the CD is recorded in 65,536 stages. The 16-bit CD recording is perfect for information. The sound between the processing stages has to be rounded up to the previous stage or the next stage. In this way, even if the information contained in the CD can be completely restored, there is an error compared with the original sound.
If the precision of the quantization is high, the more realistic and reproducible the original analog information is, the more detailed, and it is easy to draw conclusions by comparing the pictures of a 16-bit game machine and a 32-bit game machine. The quantization of the lower bits makes the quantized error larger than the high-order quantization. The error (quantization noise) generated after these quantization makes the sense of hearing spurs and turbidity, especially when the small signal is more prominent, and the harmonics of these original signals are not. The wave component constitutes additive distortion.
As a special case of digital audio, the sound quality of VCD is the result of typical digital operation. It is more hollow than ordinary CD records, lacking detail and level, and the treble spike is more prominent. This is because VCD can reproduce on a 12cm disc for both image and sound information, and use it for image and sound information. The masking effect of the human ear ignores the information that is difficult for people to detect, and performs a large amount of compression and coding recombination on the data. The process is a large-scale subtraction operation, and the final result is similar and less.
If high-bit and high sampling rate are used for digital processing, the sound quality can be qualitatively leap. In fact, many recording companies have made master tapes in the CD pre-production, such as 96kHz sampling rate and 20~24bit recording technology, but in the production. CD records, subject to the current CD specifications, had to be re-encoded to conform to the 16bit/44.1kHz format, so we can see that the 20- and 24-bit CDs are still 16-bit data streams.
If you want to change the status quo of the CD, one is to overthrow the existing CD format, using high sampling, high bit recording format and playback equipment, which will undoubtedly increase the information capacity and transmission speed. The current CD player is not competent, but the DVD is available to solve this problem. However, the recording format of high-quality audio CDs has not yet been determined, and once confirmed, it means that the CD turntable, DAC, LD, and VCD machines that have been in the market for more than a decade will become toys without the demise of CD players. doom.
Another way to solve the problem is to improve the first CD in order to achieve a breakthrough under the current system, just like the transition of black and white TV to color TV. HDCD technology is a successful and mature example of such a solution. HDCD features
In order to improve the defects of the existing CD recording format, so that it is highly compatible and can achieve breakthroughs in sound quality, Pacific Microsonics has introduced a patented HDCD recording and broadcasting technology. Its full name is High Definition Compatible. Digital, translated as a high-resolution CD. The CD-ROM encoded by HDCD is highly compatible with ordinary CDs. It can be used on ordinary CD players to appreciate the superiority of HDCD-encoded recording technology, such as CD player with HDCD decoding. You can fully appreciate the unique charm of all released HDCD information: clear and delicate sound quality, wide dynamic range, high signal-to-noise ratio, and more natural and realistic sound.
HDCD coding and manufacturing
In response to the limitations and shortcomings of traditional CD recording formats, PM's two HDCD founders, Keith OJohnson Sound Recorder and Michael W.pflaumer computer experts, have found and confirmed several key factors affecting CD sound quality in many years of sound production. And put forward practical solutions.
HDCD technology pays attention to the completeness and accuracy of the recorded signal in the pre-recording production. The analog signal is sampled at a sampling frequency of 88.1 kHz higher than the conventional one to maximize the high-frequency response and reduce the distortion distortion. The high sampling rate also leaves room for HDCD encoding operations.
With 24bit quantization, the sample value is 1677216, which is 256 times higher than the 16-bit system. High bit processing technology can improve the processing precision, reduce the quantization error, and increase the dynamic range to 120dB.
In the analog to digital signal conversion process, HDCD technology attaches great importance to conversion accuracy, and minimizes the stability of crosstalk and processing. The index that can be achieved is one millionth of conversion accuracy and the distortion component is <-120dBfs.
This high-precision, wide-band digital signal forms the basis of HDCD encoding manufacturing, and its data information is very large. It cannot be accommodated in the conventional CD PCM encoding format. If you want to play compatible on a normal CD player, you need to use special operation coding.
The use of high-sampling and high-bit technology for CD recording production has been widely recognized and widely adopted, but the reminder is that the 20, 24bit CD compact discs currently available on the market should be the number of bits used in the recording process. Due to the 44.1 kHz/16-bit standard format defined by the CD "Red Book", these high-information masterings have been re-computed to produce 16-bit CDs when CDs are produced. Therefore, the specifications that we can now interpret on CD players are still 16bit/44.1kHz. Due to the different methods used by the record companies in the conversion process, the sound quality of different versions of CDs that we can now hear are indeed different, but one can Certainly: CD quality made by high bit high sampling technology is much better than CD made by 16bit/44.1kHz recording format.
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