Feature request:
I would like to test myself in recognizing the characters/words that I have learned thru audio. can you create a quiz/review where the system plays audio, and we have to type in the pinyin and/or meaning? in this case, you would not show the character until after the user answers. In cases where two words have the same pronunciation, you can have the system say you got it right, but ask you to give another meaning (ming2 name vs. bright, etc).
thank you! great web app!
This is an interesting idea!
I think it can work for words but characters may not work. For example, the pinyin yi4 has 30 characters associated with it in the traditional course. shi4 has 23, yu4 as well
So I suppose this could be some sort of “extra game mode” section which only covers words. The question is which words to select? It could only be scoped to words recently reviewed in the last ~month or so, or all words… though I’d love to hear some opinions on which words one would want to choose 
Maybe options like
words learned in the last n days for n in {30, 7, 3, 1},HSK m word for m in {1, 2, 3, 4, 5, 6, 7-9}non-HSK wordsI think these subsets might be easier to group up front. Maybe adding in a word limit option since some of these categories could be well beyond a couple hundred words.
A long time ago I used some random website that just un-linked sounds from specific characters for all the reason Phil mentioned. Since there isn’t a nice 1:1 mapping from sound back to character, sound training can’t also be character training. But hearing shi2 vs shi3 correctly is still valuable without needing to target a specific character. If you typed in pinyin right = correct, if you didn’t = wrong. Not sure how that’d fit into HH specifically, but a listening trainer as a thing had value (although I pretty quickly transferred to full sentences as I found them much more engaging and useful).