Predicting DACs sound quality by FFT

Indeed. EQ can be powerful, but it's not magic. And if not used properly, it can sound terrible.

I'd actually submit a "truly flat" response can sound terrible, particularly after someone has been accustomed to a particular, non-flat response.

I'm sure some like the "character" of their speakers, get used to that - and when you come along and de-characterize that sound, they can hear it as something's very wrong - I cant listen to this

I think I can hear - instantly - the sound of a DAC I dont like. Would the situation be flipped if I listened to the "bad" sounding one for, say, a few months and then switched to the "good" one?

Would the situation be "what have I been doing to myself!?!" or something else?
 
Proof denies faith and without faith I am nothing -god (Douglas Adams)

Can everything be quantified? Do you have a way to scientifically say why my dog likes bananas and not peanut butter? Can you prove with math that bananas are better? Can your ears really tell you something your computer cannot? How did they cut the stone at Puma Punka?
 
Finally I was able to understand why the (sound card’s) DAC with decent FFT sounds badly.


There are 2 reasons


The 1-st (and the main) is very specific resampling made by the DAC.
The DAC doesn’t follow the data source sampling rate automatically. It has an independent Sampling Rate setting. So if the data source is of 44.1 (for instance) but the DAC is (accidentally) set to 48 the result is terrible. When the sampling rates are equal everything is as expected.
Where exactly the resampling happens (by the driver or by the hardware) – no idea.
However if the sampling rates are different, the both, the FFT and the real sound are terrible. It's especially noticeable while measuring jitter (with ARTA)



The 2-nd is inexplicable huge harmonics levels on IM high frequencies (10+11kHz/1:1, for instance)
The IM distortions go lower with increasing and decreasing the frequency, so on 19+20 kHz or 1+2kHz they “match” FFT on 1kHz, but the evident and huge maximum (-55-60db) is reached on 10+11Khz.


So my conclusion is taking care to verify the sampling rate conversion (if any) and try IM, not just THD on a single (typical) frequency.
 
If you are talking about s ES9038PRO dac, you found something but not everything. The ASRC in Sabre dacs is not the best sounding one, but it sounds much better if DPLL Bandwidth is minimized as ESS recommends.

Also, you are correct that incoming jitter affects sound quality. It is that jitter which limits the lowest stable DPLL Bandwidth you are able to use.
 
It’s not ES9038 and not a Sabre at all. It’s AK4396 (Zoom UAC-2 USB interface).
I have no any auidable problem with any Sabre staring from ES9018, may be just excepting ES9023 ;-)


And, to make it clear, jitter was practically undetectable in the interface if the sampling rate matches. Jitter was just a sign there is something odd with the sampling rate conversion in that particular sound card