The tone, accent, and tenor of Shinkansen announcements in English have changed very little since the 70s, so it's clear they make an effort to maintain consistent quality. Even so, back in the 70s, the English of the female announcer was so regal, genteel, calm and composed in an affected and controlled tone that I'm not sure that a Canadian, Australian, American, or Brit could have duplicated it, so I'd be willing to bet the earliest announcers were Japanese (though I could be wrong). After all, even back then, there were native-level Japanese speakers of English who were raised or spent many years abroad, so I'm sure there were many good Japanese candidates who would possess the requisite tone of voice for luxe Japanese train announcing. That said, this lady certainly has that Shinkansen announcer voice down.