Hi Roger

I believe that the AIFF file version of the RealTracks are uncompressed 16 bit 44.1K audio data, and the smaller m4a version of the RealTracks are compressed versions of the same.

Compression loses a little bit of fidelity. Especially if a file is compressed too much. This is data compressiion, not amplitude compression as when you use a compressor-limiter to control the dynamic range of a track.

But "CD-quality" levels of compression sound surprisingly similar to the un-compressed version. In many cases you have to listen very closely to tell any difference.

We ship so much RealTracks content, that a full install is getting pretty big even using the smaller m4a files. Unless you can hear a definite difference using the "Audiophile" version with the uncompressed AIFF files, it is certainly more convenient to use the m4a variant (and less expensive). The many hours of RealTracks content uncompressed, requires a whole lot of disk space.

It just depends on whether you want to spend more money and have a much bigger disk drive, for (in my opinion) marginal improvement in audio fidelity. AIFF will be better, but whether it will be better enough to make a practical difference is hard to say.

James Chandler Jr
http://www.errnum.com/