No, just because the tag would include a huge number of posts. It seems like a good heuristic to have dedicated tags in these cases. Moreover, the tag can be removed if we eventually don’t find it useful, whereas the reverse seems more complicated. (I emphasize that we can also tag these posts with ‘audio’; I’m only proposing that we use a special tag regardless of what other tags we use.)
If these posts are going to be tagged, I suggest using a special tag besides, or instead of, the ‘audio’ tag.
Why, because it’s a nonhuman voice?
No, just because the tag would include a huge number of posts. It seems like a good heuristic to have dedicated tags in these cases. Moreover, the tag can be removed if we eventually don’t find it useful, whereas the reverse seems more complicated. (I emphasize that we can also tag these posts with ‘audio’; I’m only proposing that we use a special tag regardless of what other tags we use.)