Hallo, first post.
Learned a lot about audio here already, and hope for more

Many thanks for that.
Out of curiosity I've been measuring my "Apple USB-C to Headphone Jack Adapter" (Model A2049) lately.
Measurement hardware is an old Thinkpad T400 running Linux and an even older E-MU 0202 USB,
both powered by laptop battery to avoid ground loops.
The Apple Adapter was first connected to a RaspberryPi 2 (for the measurements shown), and later
for cross checking the results to a Thinkpad T430s (measurements not shown, but nearly identical
to the measurements with Pi).
Both devices were running Linux with pulseaudio disabled. Pure ALSA audio, DAC volume at 100%.
First test was 1kHz, 24 bit, 48kHz, reproducing Amir's result. Good.
View attachment 50402
Next test was multitone, because I missed that one in the review.
I picked up the multitone test file Amir provided here:
Multitone test file
Downsampled to 48k with sox:
sox 'APx555 Multitone 32 192 khz 24 bit.wav' -b 24 -c 2 'Multitone_48000_24_0dB.wav' rate -v -L 48000 dither
Measurement result looked very disappointing: not even 70dB of distortion free range!
View attachment 50403
Next I 'measured' the used test file via ALSA loopback device with REW to ensure the test file does not contain any unwanted artifacts from downsampling. Test file was OK.
Maybe clipping in the DAC?
Ok, downsampled multitone file again, this time with -3dB gain, providing some headroom to the DAC:
sox 'APx555 Multitone 32 192 khz 24 bit.wav' -b 24 -c 2 'Multitone_48000_24_-3dB.wav' rate -v -L 48000 gain -3 dither
Much better, but still a bit disappointing: slightly more than 90dB of distortion free range. Even my Behringer UCA202 can do that (in 16bit!).
View attachment 50404
This was the best measurement for multitone test I could come up with.
I'm not absolutely sure that my measurements are correct,
so I would appreciate it very much if someone else would share his findings.
Until then, assuming my measurements are correct, I see two things to take away:
1) Ensure to feed the DAC with about 3dB headroom to avoid clipping.
2) Should we still call the DAC transparent, as I've seen here occasionally in some threads?
I don't think so.
Don't get me wrong. The DAC is cheap and small and good enough for many use cases. Just don't expect wonders.