Apparently slight error in pronunciation
My apologies if my comment is incorrect, I found that in the Hindi lesson, sounds associated with cu & cu- (hyphen on top) were indistinguishable. Otherwise, I am happy and will be happy to contribute towards your good services, you have my admiration.
Personally, I find the श and ष indistinguishable.
The audio for the Hindi course is computer generated using the Polly service from Amazon. This is discussed at length here: https://aws.amazon.com/blogs/machine-learning/powering-language-learning-on-duolingo-with-amazon-polly/