Is there any such thing as a bad sounding DAC these days?

@mikhailark +1

@aberyclark 
"I have the Topping E70Velvet and it sounds superb."
I am curious. How much opera do you listen to? How many Cds with sopranos do you have?

@mikhailark Reviewers like Amir at ASR also include multitone tests to look at more extensive IMD phenomena:

In terms of music comparison, there is software like Delta Wave Null Comparator that can facilitate doing exactly that. To use with DACs, you have to confront that the ADC will have digitization limitations. For speakers and headphones, you have microphone/space considerations that are better accommodated using systems like Klippel that use repeated measurements to achieve anechoic approximations in regular spaces.

I recommend Audio Science Review as a resource for learning more about measurement techniques.

@markwd - yeah, I am familiar with the guy. He is just hobbyist, some former Microsoft guy that made money on stock options and thinks he knows everything. Typical corporate VP buffoon.  Multitone is OK, but still not enough.

@chervokas - to be entirely correct, it is just Fourier Transform (FT). FFT is a Fast Fourier Transform which is an algorithm (one of many) that implements FT in discrete form for a typical computer chip. FFT is only approximation, it is NEVER precise as Fourier sequence is infinite for complex signals like music. Thus, ANY transfer to frequency domain and back (such as for Dirac) is somewhat lossy. Discrete chips and methods all have limited precision.