The main purpose of audio recordings on this forum is the performance of the music itself, rather than to illustrate the quality of an instrument, and MP3 is usually sufficient for that. The idea of audio sample files was introduced as a concession to allow exact comparisons between instruments. MP3 is a "lossy" format, as it is compressed and does not give a completely true representation of the sound, so the WAV format is specified for such comparisons. The limitation on the length of the recording keeps the filesize down (important in uncompressed formats) and avoids copyright problems. While Bach is out of copyright, Mario Castelnuovo-Tedesco died in 1963 and so his works will be protected until 2034 (70 full years after the end of the year in which he died).
If your friend joins the forum, he or she can post an MP3 of the Bach recording in Our recordings of J. S. Bach
in accordance with the rules here
(note that members can only post their own recordings in those sections). Otherwise if your friend attaches it to a video or slideshow and posts it on Youtube, you could draw attention to it in Our favourite websites
. Other than that, you can find the rules on which attachments are allowed here
Classical Guitar Forum.
"Experience is something you don't get until just after you need it." - Steven Wright