Topping dx3pro provides 6 different digital filters. Most people say they can't hear a difference. Sure the mechanics of the function of human auditory system don't really allow us to hear obvious difference of these filters. We hare most sensitive to frequency response. But we can't hear over 20khz so the difference there are not important to us. Then harmonic distortion is very common measurements for us to do. But real music are consistent of all types of harmonics and most likely our headphones have 100 times more harmonic distortion. Now that lead to the third possibility. IMD. Intermodulation distortions. There are already different ways of measuring numbers of IMD. But from my experience, they are far from accurate and won't show the whole spectrum (pun intended). So what I decided to do is to look at the frequency spectrum of different imd exciters.
(before I did the measurements, I did an extensive listening test, will talk about subjective experience later)
After I did different types of measurements from multitone, ccif, smpte, to din, aes dfd. CCIF and DFD show most difference between filters. And CCIF is just a little bit more obvious, and these two are essentially the same tests. So I'll just use CCIF for demonstration.
(before I did the measurements, I did an extensive listening test, will talk about subjective experience later)
After I did different types of measurements from multitone, ccif, smpte, to din, aes dfd. CCIF and DFD show most difference between filters. And CCIF is just a little bit more obvious, and these two are essentially the same tests. So I'll just use CCIF for demonstration.