past tense - I didn't hear what you've said

Is the sentence

I didn't hear what you've (just) said

a natural one? Some tell me that it's unnatural, but not ungrammatical. Others tell me that it's all right. I'm puzzled. What do you think? The trouble seems to be the usage of present perfect ("you've said") after past simple ("didn't hear").

Let me add a subquestion. Would you be likely to use the above-quoted sentence at all? I don't care much if it's grammatical or not, I would like to know if any native speaker speaks like that nowadays.

Answer

I think the present perfect sounds wrong here because there's no grammatical connection with the present. The connection is with the very recent past. "I didn't hear" is in the past tense, and the connection of "what you said" is to that past, so it's unnatural (and maybe ungrammatical) to use the present perfect. You can indeed say "I don't understand what you've just said", because there the connection is to the present (although I think most people would use the simple past there, as "what you just said" is a very common wording).