However, portaudio looks non-free to me.
http://www.portaudio.com/license.html:
* Any person wishing to distribute modifications to the Software is
requested to send the modifications to the original developer so that
they can be incorporated into the canonical version.
Sounds quite clearly like a request to me, not a requirement.
The difference between a non-binding request and a requirement is a
fine line especially considering why it's in the main license text not
some accompanying documentation.
Clarifying this is what is really required; moving the problematic
clause out of the way would help.