BTW, I've took some time to improve the audio modem library a bit:

• a few optimizations so decoding can run "in parallel", while the audio is being recorded.
• unit test suite with good code coverage (integrated with https://travis-ci.org/romanz/amodem and https://coveralls.io/r/romanz/amodem)
• better (and easier) command line interface for sending and receiving data.
• make the library code to be PEP8 compatible.
• add support for Python 3.
• calibration process now checks all frequencies that are used for transmission.
• improve equalization process, with better handling of signal distortions.
• I am using a hexagonal constellation grid (instead of standard QAM), to improve SNR for existing bit rate -> thus decreasing error probablity

See https://github.com/romanz/amodem for details.