Thank you Ben. This appears to have worked without actually trying to convert a file. At least the program opens.
For clarity sake for other people that may find this post…
You need to open /usr/bin/soundconverter with your text editor.
So in my case on XFCE, it is:
sudo mousepad /usr/bin/soundconverter
Replace mousepad with whatever you use for a text editor.
options, files = parser.parse_args(args[1:] if args else [])
Note: Edited the comment ‘open with sudo’ - because that’s entirely dependent on editor. Using fresh-editor, or Kate editor, for example - you only enter your admin password when you SAVE the file.