That’s like saying “no video nitrates over 10mbps will have noticeable improvement”. It’s definitely true if you’re watching, say, Khan Academy.

Switch it to a fireworks show and watch the quality suffer.

320kbps MP3 just means the codec allocates 320kb to store each second of compressed signal. Obviously some signals compress better than others and need much lower than that for an acceptable quality (audiobooks are often distributed at 64kbps).

From my own experience, 320kbps MP3 is enough to handle any music without noticable audio degradation. I have not done double blind tests, and this was in my 20s when my hearing was a lot better, but at 128 kbps I could clearly hear the loss of quality in some spots like cymbal crashes. At 192 kbps I could not tell the difference between the mp3 and lossless, using good over-ear earphones or speakers.

And as I said, the airpods are medium quality earbuds. Not bad, not great. You will NOT hear any loss of audio quality if you play 320 kbps mp3 through them.

I'm sure most people could not hear any quality loss on 128 kbps mp3 (I don't these days), or even 64. But above 320 there is just no way.

Often, when people say 'I couldn't (or cannot) hear the difference' they are not, or have not, been a/b'ing or making other technically meaningful comparisons. It is effectively saying, 'when I listened to the mp3 it sounded the same as when I listened to the lossless'. These are aesthetic remarks, which also count, but they may not be of value for everyone else.

While i did not do double blind tests, or even blind tests, I did play the problematic sections (like 1-2 seconds) over and over to be sure I could hear the artifacts. It was not some casual listening. And I could only hear the artifacts in specific places, like crash cymbals in rock music, which I never normally listen to.

Glad to hear it (pun intended, if puns are allowed).

The practical difference in the listening experience is, as you infer, negligible, to almost everyone. Classical music, or other such audio with large dynamic ranges, suffer the most. And while those frequencies above 12-16kHz are often the most obviously hit, the entire range suffers in other ways, phase, low end smearing, transient loss. And while first generation lossless to lossy conversion really is an excellent trade off, lossy to lossy very quickly produces audibly worse sound, even 320 to 320 conversion. But you knew that.

Exactly. Audio codecs for VOIP run as low as 6kbps and sound really good for voices, but completely break down if you try to play any kind of music through them.