MP3 samples are automatically generated shortly after you upload your WAV file and are only used for PromoWorx downloads/previews, as well as for your own reference within the LabelWorx system. In most cases, you won't need to generate any MP3 samples yourself.
Please note that these MP3s are not distributed to any of the stores we work with. The stores will instead generate their own samples and downloadable file formats using the WAV file which you uploaded.
You should only generate MP3 samples if you are intending on using our PromoWorx service, or if you have replaced your WAV file due to a track audio update.
If these reasons apply, then clicking the 'Make 320k' icon will regenerate the MP3 file that your DJ recipients can download, and the 'Make 128k' icon will regenerate the short preview clip.