I started work on the decoder. It works by comparing each cycle of the sine wave recorded with a certain frequency (freq_t). The function that does this currently returns the last sample that falls in that range over all samples. The longest chain to match up with a certain frequency the best is interpreted as that frequency (assuming it passes an entrance floor to separate it from static).  I will probably extrapolate the sine wave to more samples (320 kbps+), but this works OK just for testing. I am also prepping the docs per the official BIP spec.