Originally Posted by slim.a
I do remember that at some point, on Metrum's website, that they published comparisons of impulse response for NOS vs. oversampling DACs. From memory, the impulse response of the Metrum DAC looked more like analog (or DSD) than the 48K (or 96K, 192K) PCM shown in the picture above.
As for the Lundhal transformers, I don't know what to make of it.
That's true, but there's much more to the picture than that. While you may get a clean looking impulse response or square wave on NOS DACs, you'll also get stair-stepped sine waves that look like this:
An analog sine wave would look smooth, and you could make the argument that music is composed more of sine waves, not impulses or square waves. When you get to high treble frequencies, especially at or over 10KHz, the NOS sample-and-hold characteristic makes the measured signal look so stair-stepped that you can barely recognize the sine wave. One upside is that going to higher sampling rates greatly improves this. Even a 96KHz-sampled music file does wonders for this stair-stepped pattern on NOS DACs. (If you run NOS DACs, you owe it to yourself to get music at higher sampling rates or try to find software upsamplers without filter ringing.)
However, there's one idea floating around that by the time the wave goes through an amp, a driver, and hits your ears and brain, it'll be smoothed out. I think there may be some truth to this, but I'm not sure. On one hand, I've heard a NOS DAC that was able to play 0dB sine tests cleanly, subjectively, all the way up to 20KHz. This was a PCM1704-based NOS DAC. On the other hand, I've heard another NOS DAC (Metrums, TBH), that as you moved up to higher sine wave frequencies at 0dB, it would start to fall apart and sound more like a 56K dial-tone and would measure with a ton of distortion. A counterpoint to this is that music probably isn't going to have treble signals anywhere near the 0dB level, and high treble sine waves did sound subjectively cleaner and less distorted to me on the Metrums the more you lowered their level.
I know some believe upsampling/oversampling filters with pre and/or post-ringing don't have audible effects, but my (potential flawed or totally placebo) subjective tests make me think otherwise. The most noticeable, audible difference will be the slight treble droop on NOS DACs. But I do think there is something to be said about human hearing and what upsampling/oversampling filters with lots of ringing might do to the time domain in an audible manner.
There are potential trade-offs either way, in theory. I say just go with whatever sounds best to you, and I did love how smooth and musical the Metrum DACs could be. It's good to try to know what's going on with your sound on a technical level, but it's also best to trust your ears in the end and go with what works for your tastes. I know the Schiit Yggy is supposedly meant to optimize the frequency and time domains, so perhaps it'll actually be the best of both worlds. (Clean impulse and square wave on NOS being focused on time domain, smooth sine wave and no treble-droop on OS DACs being focused on frequency domain...sorta like that, if that makes sense.)
Now, as for those transformers in the Hex, I've heard some say the Quad and Octave sound more "direct" due to not having output transformers. Whatever that means. Some prefer it without, some prefer it with (Hex).
Edited by hans030390 - 10/20/14 at 12:22pm