本帖最后由 andygaof 于 2018-5-12 13:51 编辑
ronbewen 发表于 2018-5-12 03:07
有个疑问啊，高总好像从来没听过polysinc或者xtr的dsd512回放模式，貌似只升频到了256，从我经验来看，256 ...
因为我的解码Total Six只能支持到DSD64，256都是在我不常用的解码上试的。
对于升频，我觉得不同的解码结果是不同的。所以还是听听自己做决定。
Total的作者对于升频的看法如下：（摘录自Total官方网站 http://www.totaldac.com/principles.htm），大意上是说，一旦加了FIR升频滤波，方波就会出现振铃，而不升频时方波就很方。但是呢不加滤波频响就会不太好。我以前测试过几个R2R DAC也是这样，一旦关了所有的滤波用NOS（no over sampling，不升频）方式，其频响曲线就会不平直。但是从方波上，有经验的声音开发者都会明白，一旦出现振铃，那么就会意味着瞬态和微动态的共同下降，但是声音听着反而变冲。出现比较明显的假解析升高的问题。当年9018备受争议的地方也在于此，它的方波振铃很厉害，解析听着很高，曾经备受称赞，但是大浪淘沙后，最终对9018的看法声音非常不自然，没有音乐味。但是Total加了升频滤波有这个问题是不是代表所有的解码器都有这个问题我无从得知，另外有些解码器本身就方波振铃，加了滤波也不会更严重，对于这些本身声音就不太自然的解码器，声音可能就会只有好处没有坏处了。
IR compensation filter: Non-oversampling DACs are known for their musicality but they all have a problem, the frequency response is not flat and the treble loss is more than3 dB at 20KHz. This is called sinus(x)/x loss. All DACs with oversampling compensate the sin(x)/x loss in their digital filter.On the TOTALDAC board I didn't want to use oversampling because I prefer non-oversampling DAC sound, but I used a FIR filter to compensate the sin(x)/x loss.It is a short FIR for high frequencies only, so response before impact is short and is not a problem.
Frequency response at 48KHz with and without FIR filter, the response is flat to 20KHz when the FIR is used:
820Hz square wave sampled at 44.1KHz without treble compensation FIR filter:
There are no oscillations, it is the pure NOS DAC mode.The horizontal level confirms the 0Hz bass bandwidth.
820Hz square wave sampled at 44.1KHz with treble compensation FIR filter:
When the FIR filter is activated some oscillations are visible but the amplitude and the number of oscillations is much smallerthan those on conventional DACs. This is part of what explains the natural sound of the DAC.
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发表于 2018-5-12 10:19:46
楼主
谢谢高总的解答。
