Thanks. I keep forgetting how broken un/pack are in this respect. Having "B6" load the high six bits (of the low byte of the integer) is just non-sensical.

So for the most sane configuration (bits split based on base-2 representation not some "ascending bit order" representation) you have to work harder:

my @fields=
     unpack "C*",    # 16 6-bit numeric values
     pack   "b6"x16, # string of 16 bytes, each holding a 6-bit value
     map ''.reverse, # 16 6-character ascending-bit strings
     unpack "a6"x16, # 16 6-character base-2 strings
     unpack "B*",    # 96-character base-2 string
     "twelve bytes"; # 12-byte packed string
print "(@fields)\n";

my $string=
     pack   "B*",    # 12-byte packed string
     pack   "a6"x16, # 96-character base-2 string
     map ''.reverse, # 16 6-character base-2 strings
     unpack "b6"x16, # 16 6-character ascending-bit strings
     pack   "C*",    # string of 16 bytes, each holding a 6-bit value
     @fields;        # 16 6-bit numeric values
print "($string)\n";
[download]

outputs:

(29 7 29 37 27 7 25 37 8 6 9 57 29 6 21 51)
(twelve bytes)
[download]