Benchmark DAC1 采用了Analog Device 公司的新产品AD1896 数字接收芯片,而之前多数DAC都是采用Crystal 的CS8420.
AD1896 的重要作用,就是可以减弱jitter , 其基本原理在于AD1896不根据输入的数字信号来决定时间长短,而是根据DAC自带的主时钟和输入的数据平均码率来决定输出码率, 所以才能做到" 对转盘不敏感" , " 你可以用CD-ROM加Benchmark DAC1 超过一万美元的CD系统"
这里是一段英文,来自论坛的讨论:
Will AD1896 improve jitter rejection? Post #1
how to connect AD1896 to improve jitter rejection?
Is input 44.1khz and output 192khz a good idea? or the ratio should be integer?
如果连接AD1896才能改善jitter消除? 输入44.1khz输出192Khz可以吗?
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06-10-2003 03:46 AM
jwb []
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Post #2
AD1896 will attenuate jitter. Big time. Hook it up like it says in the datasheet. Ratio makes no difference, and no matter how hard you try you won't get an integer anyway. The AD1896 (and other ASRCs) use a rate estimator to determine the average incoming data rate, and use the master clock to determine the desired output rate. Then they apply digital filters to complete the conversion. The output should have the same jitter as your master clock.
AD1896可以衰减itter. AD1896通过对输入速率的估计来决定平均输入数据流.用主时钟来决定输出速率,然后通过数字滤波器去完成转换. 输出的信号的jitter 和DAC上的主时钟一样.
I don't see any reason to not go 44.1 to 192. Your DAC is probably going to oversample this to an ever higher rate anyway.
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06-10-2003 04:34 AM
yejun []
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Post #3
Is it possible AD1896 has a better oversampler than normal DAC?
AD1896超采样比普通的DAC 更好吗?
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06-10-2003 05:01 AM
machinow []
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Post #4
quote:
Originally posted by yejun
Is it possible AD1896 has a better oversampler than normal DAC?
yejun,
the oversampling is necessary for the digital filter, not anyway.
I suggest you if you use a sigma-delta DAC and no more than 44.1-48kHz source, to resample it to ONLY 48 kHz with the 1896 chip. This will leave more headroom for the digital filter, integrated in the sigma-delta, and it will use 8xoversampling /for example, see AD1853, AD1955 datasheet!/ If u resample to 192kHz, the DAC will be left with only 2xOversampling and the frequency and phase responce becomes uglier
超采样对于数字滤波器总是必要的.我建议如果你使用44.1-48Khz的数字源的话, 使用1896 把它重新采样成48Khz, 这样, 你的Delta-Sigma 方式的DAC就有更大空间,对于比如AD1853这块DAC就可以有8倍超采样.
So you can see it is significant what kind of source and DAC you will use. Many people here hate Sigma-deltas, but they are a lot Cheaper and good ones have very good Digital filters inside and characteristics also.
Regards
Kaloyan
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06-10-2003 10:11 AM
锗?怡桕 []
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Post #5
Hi All!
By the way, ad1896 wonderfully works in a synchronous mode, when it is equivalent to the ordinary digital filter with integer factor of oversampling.
From it is possible to receive 4Xoversampling for 44.1 or 48kHz.
In this mode it is comparable with digital filters SM5842/5847 and subjectively sounds better than SM.
顺便说, AD1896 在同步模式下工作的非常好. 这时候他等价于一个整数倍升频的普通数字滤波器, 他可以把44.1或48Khz进行4倍升频. 这时候,他差不多和SM5842/5847数字滤波器相当, 而且声音比后者更好.
Probably it explains in short length of the digital filter AD1896 (only 64 taps).
In an asynchronous mode, it certainly suppresses a jitter, but sounds considerably worse than SM from NPC.
这可能解释了AD1896数字滤波器的短长度(64taps ) ? (没明白)
在非同步模式下,他可以抑制jitter, 但是声音比使用SM 从NPC 中要差很多. (难道抑制jitter并不能改善声音? )
But to apply a synchronous mode it is possible only in case of presence of separate clockline for synchronization DAC with transport.
但是应用同步模式的时候, 只有在DAC和转盘使用各自的时钟的时候才可以.
This mode can be used as with R-2R DAC, and as with the delta sigma DAC as AD1955 and PCM1738 (i.e. there, where is possible to disconnect the built-in digital filter, in the other case, with ordinary D/S DAC here is no sense in it, good anything is not present in a double digital filtration, where one of them also with fractional factor).
这种模式(同步) 可以和R-2R DAC一起使用, 加上Delta-Sigma 方式的 DAC,比如AD1955或PCM1738 ( 太难,自己看吧
)
For what to use it in a synchronous mode with R-2R multibit DACs (or inputs 1955/1738 in external digital filter mode), it is necessary to AD1896 on an output to put the shift register. It is possible to carry out synchronous reclocking at desire.
The main generator and divider is necessary for establishing in the DAC module, ad1896 to establish in slave mode (in/out) completely, and requires submission of a grid of frequencies from a divider.
From the same generator the transport / decoder should be synchronized.
Regards
Halyavshick
__________________
sorry my wrong English
综上,看来有几个观点:
1. AD1896工作在非同步模式可以显著降低jitter
2. 据说非同步模式下AD1896声音没有"SM from NPC" 好 ?
3. AD1896工作在同步模式下,可以做4倍升频,并且效果非常好
看来还是有几个问题不明?
1. Benchmark DAC1 是使用AD1896的非同步模式还是同步模式?
如果是非同步,看起来比较合乎逻辑, 但jitter降下来了,声音一定好吗? 如果好,那么天价转盘就没必要了
2. 如果是同步模式AD1896,那么4倍升频会不会带来惊喜? 那么天价转盘还是必要的了.
