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45楼
发表于 2018-3-8 21:28
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来自 美国 弗吉尼亚州劳登县阿什本地区Verizon
出处：https://www.head-fi.org/threads/ ... dave.766517/page-82
post 1220
Going back to when Hugo first came out, I noticed different SQ with different lap-tops and PC's.
Now the problem is definitely not jitter from the source - my DAC's can tolerate 2uS of jitter and it will have zero difference to the measurements - also the USB is isochronous asynchronous so the timing comes from the DAC clock, so source jitter is not a problem.
So I looked into the issue of different SQ with sources and found two sources of error:
1. RF noise. RF noise is a major pain with audio. With analogue electronics, very tiny amounts of RF noise will cause intermodulation distortion with the audio signal, and the intermodulation products is noise floor modulation. The effect is that the noise floor changes with signal level, and the effect is very audible - you perceive it as a brightness to the sound quality. Less noise floor modulation, smoother sound quality. The curious thing about this is that the brain is very sensitive to it, so you can easily hear it. Problem is that many listeners hear the brightness as more detail resolution, and so think it sounds better - but that's another story.
2. Correlated current noise. If a tiny current that is signal related but distorted enters the ground plane, then this current will be a source of error, as the current in the ground plane induces small voltages. Now this then adds or subtracts to small signals, thus degrading small signal resolution - and this upsets the brains ability to calculate depth. Now one of the most fascinating things I discovered with Dave is there is no limit to how small this error can be without a degradation in depth perception - so it does not matter how small the error is it will have an impact.
So the solution to the above problems is galvanic isolation. This means that RF noise from the source can't get into Dave, and small correlated currents can't get in too. And this approach gave two benefits - much smoother sound quality, and a deeper soundstage.
Now with Dave I can no longer hear which source is connected, but before without the galvanic isolation it was easy to hear. Additionally, optical sounds almost identical to the USB, as optical is clearly galvanically isolated too.
大意就是：rob能听hugo而辨别使用的数字源。但因为他设计的设备最高可以承受2us的jitter而不影响音质，所以导致声音有区别的原因不是jitter，而是以下两个方面：一个是射频噪音，另一个是电流噪音。他通过在dave上增加USB电气隔离的方式避免了这两种噪音对音质的影响，因此他现在用dave已经听不出dave前面使用什么数字源了。所以目前来讲，在dave上使用USB是性能最好的输入方式，其次是光纤，因为光纤因为自身原理，本身也是电气隔离的，而同轴界面则是最差的。
2qute的usb同样带galvanic isolation，所以以上结论一样成立。
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