I enlisted my wife to be part of a blind study this morning. The upsampling toggle switch on the CDT Mk3 is on the back of the transport, and it makes no audible noise when clicked up and down. She would be toggling the switch up and down in no particular order and would be asking me at each rest point of her choosing whether the toggle was in the up position or down position. Down is 44.1. Up is 176.4. I also placed a cloth cover over the front display on the Holo May DAC, so that the I could not see the state of the sampling.
The test was simple. She was to toggle the switch up and down in no particular order while I listened, At any point of her choosing she would ask me whether the toggle was in the up or down position while I listened to the music. We were listening to the first track of James Taylor’s album "October Road" which has always been one of my favorite test tracks in general. Since my wife loves to mess with my head, I was confident that she would randomize the heck out of her toggling. Since the toggle takes about 5 seconds to refresh the DAC screen we had to "pause" the track whenever its position was changed. She was free to say "pause," wait 5 seconds for the screen to update even though she had not changed the position of the toggle and vice versa. After about 20 cycles and swtcheroos - whether or not there had been a switcheroo, I asked her how I had done. She was somewhat annoyed that she had not been able to fool me. I correctly identified the position of the toggle every time. The difference was so obvious that even she - who does not pay any audiophilic attention to music - could hear differences.
I am wondering whether R2R DACS such as my Holo May are more musically agreeable to upsampling and also whether the GanFet amps such my Audions are also more sensitive to upsampling. The arguable technicalities, however, are not really my concern here. If it sounds better - I do it.
https://www.audioholics.com/audio-technologies/upsampling-vs-oversampling-for-digital-audio