I use my iPad for ear training and I can absolutely tell the difference between my DragonFly red and the Apple USB-C DAC. I'm just better with the DragonFly.
Don't get me started on the Bluetooth headsets. For music they are ok but there's really basic interval training that I score 100% on with the DAC and like 80% with Bluetooth. Consistently.
I use Complete Ear Training for interval training, with the grand piano or the Rhodes sound pack. I switch pack every once in a while. I also use TonalEnergy Tuner to sing intervals or scales to it and see if I'm in tune.
In something like a year I went from "telling apart major and minor thirds is black magic" to being able to sing the major scale right like 60% of the time and I have an 80% success rate for all intervals up to a fifth. It did improve my piano improvisational skills by a lot.
It would likely be quite easy if you could compare them back to back, as in swapping from one to the other and playing a controlled source with a hi-fidelity amp and good headphones. The analog side of digital-analog conversion is an art unto itself and I've found a lot of variance between DACs, even though I'm neither a sound engineer nor an audiophile. If you are just playing a 64k AAC file on your EarPods, probably not.
The Apple USB-C dongle is actually pretty well regarded as an inexpensive step up from onboard audio for “normal” headphones, and some folks will use it as a starter DAC to pair with an amp for less “normal” headphones …
That's interesting. It looks really tiny on their site, so I guess the analog signal must be generated in the computer? So it seem more like a "PC manufacturers typically put more effort into their USB implementation than their 3.5mm implementation" sort of thing, I guess?
Don't get me started on the Bluetooth headsets. For music they are ok but there's really basic interval training that I score 100% on with the DAC and like 80% with Bluetooth. Consistently.