Audio Converter Pro Help - Purchase - Download - Acoustica
The option "Never create files higher in quality or size than necessary" at the bottom of the MP3 Options dialog will make sure that the software does not "over" encode any MP3 files.
When reconverting in batch mode you may not want to have some low quality files reconverted to larger files if the quality does not improve.
For example, if you have an 11,025 Hz WAV file and you have you’re MP3 encoding options to create 128 kbps MP3 files, this option will make sure that a more appropriate MP3 format is chosen. In this case, it might choose 64 or 96 kbps MP3 files.