A sound-based puzzle sounds great! I found it hard to make out the very small differences in tone- I think a button to replay what you've entered before submitting it would be a great quality-of-life change. And maybe, at least in the earlier levels, some sort of feedback to show that you have it partially right would help? I did not make it past even the first level, although I got maddeningly close (at least to my ears). Perhaps people with musical training would find this easier. But the concept is great, and I would absolutely play more of it!