I am a speech scientist and member of the Acoustical Society of America. I have never put much stock in ABX tests to tell anything but the most egregiously audible differences in the sound. Is there a scientific publication which proves that if you can't hear a change in an ABX test, it is not audible? I don't know of one. There are other possibilities for testing audibility of changes in the sound, such as sound morphing during playback. But even these are limited because they fail to account for the evolving nature of every sound.