FLAC is already a compressed format: AIFF isn't. There's always a tiny overhead when converting because of inevitable miniscule errors in the resampling, but these are likely to be insignificant and AIFF won't lose anything for you.
FLAC is already a compressed format: AIFF isn't. There's always a tiny overhead when converting because of inevitable miniscule errors in the resampling, but these are likely to be insignificant and AIFF won't lose anything for you.