My colleague (a native Mandarin speaker) insists they are the same sound, and thinks I am just confused because one speaker has a higher pitched voice. He said something about one speaker having a more feminine voice, but I'm not sure which of the two he meant.
I'm happy to accept that I'm tuning into a non-key part of the phoneme, but to my ear these sounds sound consistently very different from speaker to speaker.
The Wikipedia page on Mandarin phonology has an explanation for the variation:
I've also heard other speakers where a sound more like the English Y was more prominent. Is this difference something native speakers notice? Is it considered a regional variation, or as my colleague seems to be suggesting that one is more masculine and the other more feminine?