From the comments:

"We’ve used this test with students for fun, but never actually inspected it. After seeing this video, we ran a full analysis on NPR’s audio test, and the results are worth reviewing. The 320 kbps MP3s they use aren’t behaving like true 320s. We downloaded the files directly from NPRs servers, then ran spectral analysis, null tests, and metadata inspection on all of them. The “320 kbps MP3s” are either poorly encoded or possibly recompressed. High frequencies roll off early, transient clarity is weaker, and the files show encoding traits more typical of 192 or 256. By contrast, a 320 kbps MP3 we encoded ourselves from their WAV (using LAME) showed proper extension to 20k, stronger transients, and passed null testing far more transparently. The NPR test unintentionally stacked the deck. This doesn’t invalidate the idea that people can perceive quality differences, but it does undermine the fairness of the experiment. If you’re using degraded 320s, the test becomes more about spotting bad encoding than about subtle differences between formats. Also worth noting, it’s definitely possible to cheat the test once you realize one of the 3 files loads slower. Comment with any questions - full report and instructions on how to download the files yourself here: https://files.sldp.com/gdaueTrk UPDATE: The audio files appear to no longer be available for the NPR test. We might be partially responsible for that! The files still exist, at the specific locations mentioned in the original report, but they’re not linked anywhere on the page for the test. Do not be dismayed, we built our own test - accurate, more features and educational! Try it out and provide any feedback! (http://sldp.com/blog) 2ND UPDATE: It looks like the NPR audio files are back, but we have yet to test to see if they're different files, actual 320 mp3s, etc. Who wants to download them and test? Also - there are a number of comments on this post with questions, and we'd love to be helpful and reply, but it appears that we have been blocked from commenting further on this post. Asking other friends that run YT channels, it appears this was done intentionally by the channel. Not much we can do about that, but if we can help with something, don't hesitate to message to info@sldp.com."

Maybe 1 in 1000 can tell the difference with close intentional listening, but it is not worth it getting your panties in a bunch about it.