I record screencasts on a PC with Camtasia Studio. I like to do some audio post processing on my Mac with GarageBand. I've noticed a strange problem. When I produce an audio only mp3 from within Camtasia, it plays and sounds fine. However GarageBand corrupts the file in unpredictable ways when it imports it. Most often it drops a few seconds here and there but sometimes it will lose as much as 30 seconds of the recording. I have certain mp3 files where this is repeatable over and over. I’ve even tried exporting and then importing .wav files but this also suffers corruption (in the form of really loud screechy noise and hiss in sections). These are pretty standard 16 bit mp3 files sampled at 44.1 KHz, Mono 128 Kbit/sec. They sound fine and complete when played on either computer. Many times short files will not exhibit the problem and a couple of times larger files have worked. Generally though once the audio is about 5 minutes in length I start to see problems. I had this problem in both GarageBand 09 and GarageBand 11.
I finally discovered a solution today. I first double-click the mp3 file, and import it into iTunes. Then inside iTunes right-click the file and select Create MP3 Version. I know it's already an mp3 but the exported file from iTunes then works fine in GB. (If you have some other Create… version showing then use the General tab of the iTunes preferences to set it to MP3 as shown in the image at the left). I tried changing the settings to the AIFF Encoder but this did not work. I ended up with the same screech/hiss artifacts as when I exported WAV files from Camtasia.