I've used the free version for several months. I was searching for a way to get good quality audio conversions of some choral singing from .wav files into 96 kbps mp3 files.

Audio Hijack Pro will do truly excellent conversions from .aiff or .wav to 96kbps mp3 but it won't do batch processing so you have to do each conversion individually and wait for the process to complete before going ahead to the next one.

iTunes will do batch processing to 96 kbps mp3 files but the results are not good- voices sound ragged on many occasions- a very inferior result to Audio Hijack Pro.

Switch uses much superior LAME software and batch processes perfect sounding files (to my ear). Just drag your WAV files into the window of Switch, choose .MP3 output (having preset the desired quality level in the preferences) and press the button.

Switch cannot process files to m4a files. This process is not even offered in the pay version for Macintosh (but it is for Windows). No problem here- iTunes does an excellent joy converting files to 128 kbps m4a files.

The paid version offers a lot of extra features.

You need to look for the correct download link on their webpage to get the free version.