→ padro:其他我想問的前面louis0407兄已經幫我問了 XD 07/08 19:46
※ 編輯: padro 來自: 140.113.27.50 (07/08 19:47)
推 john0312:專業文推. 07/09 09:24
這邊我要澄清一下
Blu-spec CD
跟
Blu-ray Disc
是不一樣的 XD
前者(Blu-spec CD)
其實還是CD
只是使用了BD的一些染料技術
在bit-rate或取樣上並無與CD有所不同 (這點與SHM-CD是相同的)
前面我有提到
即使是相同的母帶
譬如說K2或K2HD使用的取樣就跟44.1kHz/16bit的CD並不盡相同
所以我不拿XRCD來探討
另外 SHM-CD (Super High Material CD)不是只有在CD本身的材質跟切割上有差異
bit-rate或是sampling沒有不同不是嗎? @@
還是說是我記錯了?!
anyway
即使是CD
各家仍有強調24bit或20bit sampling之後
以16bit re-sampling
加上mastering過程的差異
所以前述我談的是
在同一地區所發行之CD、Blu-spec CD、SHM-CD (同一張專輯之不同版本)
Mastering問題排除在外
這樣的條件控制目的在於CD、SHM-CD以及Blu-spec CD所存放之音訊資料為相同
再來做後續的比較 :)
※ 引述《john0312 (Chen John L)》之銘言：
: 對於不同的CD格式, 我們首先要看的, 是數位資訊如何的存在這些載體當中.
: CD 是採用 44.1kHz/16bit Stereo Pulse Code Modulation
: SHM-CD 是 2.8224 MHz Direct Stream Digital ( Please refer to that
: oversampling thing )
: BluRay disk則不一定, BluRay支援許多格式(PCM, Digital Dolby, DTS... etc), 而且
: 有一些還是有損壓縮, 而實際使用的格式才能決定他的品質.
: 也就是說, 從這些光碟裡面讀出來的資料不一定相同. 我猜測BluRay裡面你們聽到的應該
: 是192kHz/24bit PCM, 因為其他幾乎都是有損壓縮格式. 如果他採用有損壓縮格式, 音質
: 必定會下降.
: 另外, 這三種格式的物理結構也有差距. 例如說BluRay的資料層較接近於表面, 所以他比
: 較容易被刮傷. 這些都會影響音質.
: ----------------------------------------------
: 再來討論CD to CD variation. 感謝louis0407兄提出的兩篇論文
: 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
--
同名專輯
http://lopadro.blogspot.com/
--
※ 發信站: 批踢踢實業坊(ptt.cc)
◆ From: 140.113.27.50