* Determine how and when the SID filter op-amps clip. Spice may perhaps be
  used to simulate the filter circuit.

* Use splines to specify filter cutoff frequency characteristics. This will
  facilitate interactive manipulation to approximate the filter of any SID
  chip.

* Model the audio output stage in the C64. This does high-pass filtering and
  may have audible effects.

* Write documentation. Possibly a paper describing how SID was reverse
  engineered.

* Implement a SID tune player. Put on ice because of the SIDPLAY support.
