Using bitwise operators won't work because te masked bytes will be null; which are still characters.

Faster that split would be to use unpack:

#! perl -slw
use strict;

print unpack 'x3a7x2a4x2a7', $_ while <DATA>;

__DATA__
0121012102??????????12121212????????
0111011102??????????12111112????????
0111011102??????????12111112????????
[download]

Produces:

C:\test>junk55
1012102??????12121
1011102??????12111
1011102??????12111
[download]

Possibly faster still would be to set up an array of substr refs into a single buffer:

#! perl -slw
use strict;

my $buf = chr(0) x 400_000;
my @refs = map {
    \substr $buf, $_->[0], $_->[1]
} [3,7],[12,4],[18,7];

while( <DATA> ) {
    substr( $buf, 0 ) = $_;
    print map $$_, @refs;
}
__DATA__
0121012102??????????12121212????????
0111011102??????????12111112????????
0111011102??????????12111112????????
[download]

Produces:

C:\test>junk55
1012102??????12121
1011102??????12111
1011102??????12111
[download]

You'll have to benchmark to see if whether the latter which was once faster on some earlier version of perl still is on yours.