I'm surprised by the cross over distortion. I don't see it when measuring the outputs of my M7 (using Rigol DSO)... Will post a SS when I'm not posting from iCrap.
I'm not experienced on the matter, and the FFT measurements show all other signals other than fundamental are near noise floor. But I wouldn't of expected it in a device where fidelity is meant to be the main goal...
The M7 has a sign magnitude DAC (PCM1704) that is actually intended for audio.
Because it is sign magnitude the MSB doesn't 'topple' at the '0' Volt point but it does at the -6dBFS point instead where it is 'masked' by the large signal level.
The chip (AD5791) used in this DAC is not designed for audio in a sense that it needs another physical input signal (non standard audio related format) and post processing of the analog signal (deglitching) compared to chips designed for audio.
Because of its wide operating temperature range and stability it has been approved/designed for military and aerospace.
Not because it is more accurate or 'better'.
The somewhat confusing part here is that Schiit uses 2 of these chips per channel and claim 21 bit resolution so it stands to reason mr Moffat made it signed magnitude as well.
As the smallest 'step' of the PCM1704 is 23 bit (accuracy seems decent so who knows how small the steps can be) and the AD5791 is 'merely' 20 bit the accuracy of the first steps of the 1704 are likely to be better as in more accurate as theoretical the smallest possible step is 8x smaller in the PCM1704.
The large amount of spikes that run fairly high in level compared to most other DAC's around are caused by the LSB step size most likely or a very, very small DC offset in the DAC output signal which would only be a problem if used in signed magnitude configuration.
Again, that chip isn't designed for this specifically.
It stands out even more because the noise floor of the analog section is very good as well.
In practise it is too bad that extremely low noise floor is decreased by say 20 to 30dB as when music is played there will be lots more 'poles' all over the freq band creating a higher noise floor.
I wouldn't care about this because I would like to see a recording that actually has a noise floor below -100dB anyway.
However, like with everything else it's not just the DAC chip that matters but the implication.
The digital and analog signal handling, PCB design, power supply and other used parts are of greater importance.
I seriously doubt if any 'garbage' below say 120dB would be audible as you would have to play extremely loud for it to reach audible levels.
At least that's what I think.
Aside from that, Schiit uses magic in their designs where AGD just uses chips.
It seems to me mr. Moffat knows his Schiit and if its good enough for the goose .....
And ... did I tell you I am impressed with the amount of jitter (even though I could not care less about this)
