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.

Tangentially related: what tool(s) do you use for ear training on iPad?

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.

IIRC the iPhone dac/amp is supposed to be fairly decent for driving, like, normal headphones. At least in the past (not sure in the post-dongle days).

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?

It's even more interesting, there really is a tiny DAC embedded in the Lightning connector:

https://www.ifixit.com/Teardown/Apple+Lightning+to+Headphone...

Neat! I had no idea. Wonder if their USB-C version is better than the one that came with my non-Apple laptop...

sadly, it doesn't support mic if on windows - at least last time I've tried

Absolutely, and if I had an iPhone at the time I probably wouldn't have bought it.

I only started bothering with discrete amps when I picked up headphones with a 600 ohm impedance.