Regarding your query, Dropbox doesn’t modify your files in any way. However, there are very rare circumstances when a file can be ‘changed’ in some manner, though this is unrelated to Dropbox.
The first, and ‘most common’ is a third party app is affecting the file. This could be that a virus scanner is checking the file, and yet affects the original. Maybe on the originator’s end there was a similar issues, it’s hard to tell.
Another, albeit rare possibility, is that downloading through the browser itself could be the issue. While Dropbox can preview WAV files, it is subject to the limitations of the browser, likewise with downloading them. Again, this is very rare, but can happen.
Overall, in answer to your question, we’ve had many users sync high quality, uncompressed files, WAV, FLAC, APE etc, and none have experienced any issues. For those users that did experience some form of compression, corruption, or other matter, then it was usually due to an interrupted upload/download, poor encoding to begin with, or even not have the correct codec to play the file at the destination.
Even WAV files have codecs on how it reads the uncompressed music!
Hopefully this should clarify matters for you, however if you have any questions, feel free to let me know!
Dropbox Staff
