对於不同的CD格式, 我们首先要看的, 是数位资讯如何的存在这些载体当中. CD 是采用 44.1kHz/16bit Stereo Pulse Code Modulation SHM-CD 是 2.8224 MHz Direct Stream Digital ( Please refer to that oversampling thing ) BluRay disk则不一定, BluRay支援许多格式(PCM, Digital Dolby, DTS... etc), 而且 有一些还是有损压缩, 而实际使用的格式才能决定他的品质. 也就是说, 从这些光碟里面读出来的资料不一定相同. 我猜测BluRay里面你们听到的应该 是192kHz/24bit PCM, 因为其他几乎都是有损压缩格式. 如果他采用有损压缩格式, 音质 必定会下降. 另外, 这三种格式的物理结构也有差距. 例如说BluRay的资料层较接近於表面, 所以他比 较容易被刮伤. 这些都会影响音质. ---------------------------------------------- 再来讨论CD to CD variation. 感谢louis0407兄提出的两篇论文 I've checked the Audio Engineering Society, and discovered that the two abovementioned paper actually cost twenty USD each. Therefore I doubt if you have actually read them before. I've to admit that I myself have not read them before as well, as I am not that rich to buy that paper. However, I have found later papers that are done by the same authors as the two abovementioned paper (Ian Dennis and Julian Dunn). The paper discussed the various possibilities that will cause two numerically identical Compact Disc to sound different. First of all, if the same digital data is feed to the DAC, it will produce the same analog waveform everytime, no matter where the digital data is from. However, there's one exception to the above statement, that is the power supply. We have to be aware that the two stepper motor used in the CD-ROM drive is inductive load, and due to the fast changing current, will cause the positive power rail to flunctuate if the power supply is not well designed. If the positive power rail flunctuates, it will be coupled into the internal Zener Diode voltage reference of the DAC. However, in modern CD Player design, the power supply for inductive loads ( the two motors ), the digital loads and the analog loads are completely seperated, that means it will not cause any observable change in the DAC output. Therefore, whatsoever that causes variation between CDs will cause the input to the DAC to change as well. In the paper, the authors addressed several issues, such as the different ways that a PCM signal could have been encoded in the CD-ROM, which might lead to differences between the master recording and the pressed CDs. As I've mentioned before, in the old times, because hardwares are not capable of that much calculation, they do not check if the data they read is erroneous, which leads to errors ( the so called jitters ) being passed onto the DAC, and leads to degradation of audio quality. In the paper, the author also carried out one mass listening test, and one "golden ear" listening test. However, neither of the two listening test is able to show that the difference between CDs, if any, is audiable, even to expert listener, or the so called "golden ears". In conclusion, if we are able to ensure that the motor noise doesn't get coupled into the sensitive analog circuits, and if use error correcting softwares to ensure that the data read from the CD-ROM drive is correct, we can be assured that there is no variation between audio CDs that are numerically equivalent. EDIT: The paper is at: http://www.prismsound.com/m_r_downloads/cdinvest.pdf --

※ 发信站: 批踢踢实业坊(ptt.cc) ◆ From: 220.133.76.65 ※ 编辑: john0312 来自: 220.133.76.65 (07/08 11:37)