cbmtape: sync ((marker octet)* D sync)*
264tape: sync ((marker octet)* C sync)*

sync = [AB]*
(byte) marker = DC
octet = 0*(10*10*)*10*, 9 bits (odd parity), _least_ significant bit first
0 = BC
1 = CB

A = pause
B = short pulse
C = medium pulse
D = long pulse