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Junior Member
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引用:
Originally posted by rswill
很明顯adelies兄只是在說客氣話,不過某仁兄好像趁機吃了他豆腐
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???
原來您還沒看出某些資料所代表的涵義
恕小弟再提醒您一次
根據下文資料(1999年2月)
(摘自 http://www.geffers.demon.co.uk/cd.html)
引用:
The First Stage of Error Correction
.....Some CD players attempt to fix two errors, which is possible if there really are just two errors, however the mathematics is not so reliable for more than two errors. Several errors could create a situtation that looks like only two errors, and we can end up with a frame that we think is good, but is in fact bad.
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截至1999年為止
(當時)還只有部分的player的C1解碼運算
可以做到更正1個frame裡面有2個錯誤
所以更古老的晶片
的確在運算能力上不如現在想的強大
只能處理1個frame裡面有1個錯誤的情形
所以當C1高到一定程度
代表錯誤密度高到一定程度時
1個frame裡面有2個錯誤的現象就會變的較嚴重
古老的晶片就解不開了
這情況就可以解釋為何古老player不收C1高的片子
也可以解釋古老VCD player碰到輕微刮傷就有馬賽克、停格
1999年左右的晶片
由於運算能力的強大
所以一些player會解1個frame裡面有2個錯誤的現象
只要您肯花一些時間去推敲一下C1解碼的演算法
就會知道，其實解2個錯誤還不算難
只是要花的時間會變多而已
其實整個C1C2解碼的流程，又更複雜
所以晶片的設計和運算能力
的確會關係到是否能順利解開更多的錯誤
請仔細看如下adelies兄亦引用過的話
(摘自 http://www.geffers.demon.co.uk/cd.html)
引用:
Is There Any Way to Fix More Errors!?
The way CD players are currently built relies on a very limited hardware set of RAM, i.e. temporary storage. Given some more space, various options open up for correcting more errors.
With a 4K buffer to hold the data between the C1 and C2 stage, it is possible to redo the C1 fix-one-error operation after you have done the C2 fix-four-errors stage. Since each byte of the C2 stage comes from a different C1, any time that we correct a C2's error, we can go back to the C1 of which that byte was a part, fix a single error if possible, and clear the flag that marks that C1 frame as bad for the C2's yet to come. This means that at best we can be fixing 32 errors at C1, and also 28 errors at C2, but those are extreme conditions. Often of course you will be fixing C1 errors too late to benefit the C2's that have already gone by, but on average you will be fixing about 40 percent more C2 errors. Given infinite storage and processor power, you could continue to reprocess C1 and C2 frames, but since decoding is normally done real time, this is not usually practical. This is a fairly radical correction strategy described in this paragraph, please contact me for more information.
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小弟請您仔細看過adelies兄所提示的資料
就會理解為何adelies兄後來也認為早期的晶片很遜 |