Waveforms 0000010011111011 and 0000011011111001
Waveforms 0000100011110111 and 0000111011110001
Waveforms 0001001011101101 and 0001011011101001
Waveforms 0001010011101011 and 0001101011100101
The tone generators of the 6560/1 VIC chip are capable of producing 15 extra waveforms, in addition to the square waves they were intended to produce. The above charts show the amplitude of the harmonics of these waveforms, using a Fourier series expansion, up to the 17th harmonic.
4 of the waveforms turn out to be duplicates, so there are in fact 11 new sounds in total. All of the sounds have odd-numbered harmonics only. The waveforms are listed in decreasing order of first harmonic amplitude.