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原帖由 a.f 于 2006-5-15 23:56 发表
dat最有优势的地方就是听感,模拟味好,但兼顾高解析和大动态
和它用磁带作介质是有关系的。
还磁带介质呢,拜托不要再我们这些人当文盲忽悠 了.
DAT储存的是什么信号?????数字信号!!! 你当还有分金属带,塑料带只类的分别吧??
数字信号,说得简单点,就是把模拟信号处理成由01组成的一系列的数字流.它的优点之一就是对储存介质要求极低.为什么这么说呢????
举个例子,大家都去超市买过东西,那里的物品都有条形码标签.以一系列的粗细线条表示其物品价格...在结帐的时候,扫描器可以在隔着数层塑料带的情况下读出来,为什么???这就是它的优势了,不管它的信号多模糊,只要我们读出它的粗细间隔就可以得到我们想要的信息.
CDDA格式也是这样,一段同样的音乐,如果在DAT带上是010010101010101,在CD碟上也必定是010010101010101,这与用的什么介质无关,不是说转到CD上就成了000001111111了..
那么有人就要问了,按你这么说是不是CD原版和盗版不是一样了么?DAT母带和翻录带不也是没有区别了吗???
这里就需要我们认识数字信息的大敌,JITTER了.在数字时钟频率不一样的条件下,JITTER是无法避免的.相关的理论太过复杂,耳机上面谈得多这里不再重复..
DAT同样不能避免JITTER(如果避免了那这个世界真的就是DAT的天下了,呵呵).
国外的技术论坛上有人如此解释:
Ok, now we're talking about jitter as it is written onto the
DAT tape ?!?! I always thought the speed of the DAT head spinning
was locked to the PLL decoding the digital input (while recording).
How else could you record digital 44.056 and play it back at 44.1?
On the U bits, the rotation of the head is sent out as a single bit
click every time the head makes one rotation. I've watched this bit
and can tell you it is NOT constant.. yeah it's 2000rpm +/-.. but the
time between each click is not completely consistent.
When you record onto DAT, the PLL provides the master clock for the
whole enchilada, the DAC and digital out (for monitoring the recording)
AND the head rotation and probably tape speed. You have to lock to
your source because not everything out there is EXACTLY 48 or 44.1
... I've seen CD players that play at different speeds.. and I've seen
DAT decks that play the same tape at different speeds... mind you nothing
you would hear, but with the right equipment you can detect these changes.
similarly when you record onto the Hard Disk, you lock the PLL and it
dictates how the samples are written to disk.
When you play back from DAT, you base your whole system (DAC, head
speed etc etc) from a crystal oscillator inside the DAT machine... this
is how a tape recorded at 44.056 or 44.098 or whatever can end up
playing back at 44.101 on one DAT deck and 44.099 on someone elses
DAT deck. Similarly when you playback from the hard disk, the system
clocks off a crystal oscillator on the soundcard... well, unless you
have a ZA1 then you need to slave from another deck.. but that's
a bird of another color :) or something like that....
也就是说DAT的JITTER是无法避免的,再加上DAT是接触性读取,磨损不知比CD多了几倍,所以磁鼓的寿命比光头短.这个相信不用多解释..
至于换磁鼓,那简直是个笑话,纵然你有牛比的动手能力,但SONY的D100早就停产,哪里去找磁鼓????
又在坏的YLJ上拆???退一万步,你有多少个磁鼓换??换过以后没有专业器材全靠手动能不能保证好的状态还是另外一个问题............
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