Duplicate identification

[BookOfBen]

You could check if the filename of the audio being uploaded is identical to any of the last 20 files uploaded, and flag it to the user as a potential duplicate.

[Czar]

Thank you for your suggestion. How often this happens as it will require some time for development and implementation?

[Hernan]

The problem would be when the person uploads the first part and then, the second part of the sample (unless he states that for sure).

[BookOfBen]

Czar, my guess would be four times a day, but that's probably skewed, since I figure I'm online when the site isn't as active (due to my timezone). Your moderators would have a better idea.

Hernan, that's why I mentioned to flag it, rather than outright prevent it.
Another option would be to let the user do it without issue, and flag it to the moderators to check.