这边我要澄清一下 Blu-spec CD 跟 Blu-ray Disc 是不一样的 XD 前者(Blu-spec CD) 其实还是CD 只是使用了BD的一些染料技术 在bit-rate或取样上并无与CD有所不同 (这点与SHM-CD是相同的) 前面我有提到 即使是相同的母带 譬如说K2或K2HD使用的取样就跟44.1kHz/16bit的CD并不尽相同 所以我不拿XRCD来探讨 另外 SHM-CD (Super High Material CD)不是只有在CD本身的材质跟切割上有差异 bit-rate或是sampling没有不同不是吗? @@ 还是说是我记错了?! anyway 即使是CD 各家仍有强调24bit或20bit sampling之後 以16bit re-sampling 加上mastering过程的差异 所以前述我谈的是 在同一地区所发行之CD、Blu-spec CD、SHM-CD (同一张专辑之不同版本) Mastering问题排除在外 这样的条件控制目的在於CD、SHM-CD以及Blu-spec CD所存放之音讯资料为相同 再来做後续的比较 :) ※ 引述《john0312 (Chen John L)》之铭言： : 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 -- 同名专辑 http://lopadro.blogspot.com/ --

※ 发信站: 批踢踢实业坊(ptt.cc) ◆ From: 140.113.27.50 ※ 编辑: padro 来自: 140.113.27.50 (07/08 19:47)