Scientifically speaking, it should be noted that the adapter performs exceedingly well to the point of audible transparency[1]. You are not going to hear the distortion components as they lie below 90 dB.
The fact of the matter is that your ears simply cannot be trusted, not when it comes to discerning differences in DACs and amps. There is a beautiful read[2] that illustrates this by NwAvGuy, it's worth checking out even for non-audiophile.
And Xiph's Digital Show and Tell[3] (again, a must-read) tells us that the 44kHz of the dongle is more than enough for audible transparency to humans.
The differences you hear are likely due to incorrectly matched volumes. If you volume-match to a fraction of a decibel, you probably would not be able to tell the difference in a blind test. There are other potential differences like a different impedance etc but these should only effect a very small subset of IEMs, let alone your headphones.
[1]: https://www.kenrockwell.com/apple/lightning-adapter-audio-qu...
Regarding volume matching, with the SE headphone jack I could put the iOS volume around 40% and very much enjoy the sound. With the dongle I lost a lot of low and high end at 40%, and to bring them back to my typical volumes required iOS volume to be around 60-70%, and caused distortion around the low-mids. Yes, I tried another dongle.
I'm perfectly comfortable with trusting my ears, since that's the whole point of audio - making my ears happy.
Could you mention any better-performing DACs for $9? AFAIK none exist, which is in part the point of the linked post.
> I'm perfectly comfortable with trusting my ears,
Sure, but then you can't really make objective statements like "this distorts" when measurements are to the contrary and all modern audio science tells us your ears are probably wrong about minute differences like these.
The iPhone 6S costs much more than $9.
> I can see you're a bit of a lost soul so I'll stop trying to debate now.
I've provided sources for all of my statements. You've provided none. Feel free to ignore established science.
https://kenrockwell.com/apple/lightning-adapter-audio-qualit...
According to those measurements the adaptor's DAC is fantastic, especially for a $9 part.
And in the spirit of anecdotes, the old iPhone DACs were notoriously hissy and weak, and if you're buying high impedance headphones you have no business plugging that into a phone's headphone jack... spend the $20-50 on an amp/DAC and call it a day. Just a bigger dongle.
> certainly better than
> the Android ones that
> just pass analog through
> the USB-C jack
For me, they sound good driven from my iPad pro and a USB C charging/headphone adapter so I listen from that at my desk.
That is backwards. Lower output impedance is better as more power is delivered to the load all other things being equal.
[1] https://ifixit.org/blog/8448/apple-audio-adapter-teardown/