Convert audio using ffmpeg.

batch_audio_convert.txt

1. Download the binary ffmpeg: http://ffmpegmac.net/
2. Extract the executable ffmpeg file. 
3. Copy it to a directory that is in your executable path, e.g. /usr/bin.
    sudo cp ~/Downloads/ffmpeg /usr/bin/ffmpeg
4. Make it executable:
    sudo chmod +x /usr/bin/ffmpeg

Now, in the folder with the AIFF files, run this:

    for f in *.aiff; do ffmpeg -i "$f" "${f%.aiff}.ogg" -aq:a 2; done

Where:
  -aq:a 2   <- This sets the audio output quality.