[mattr@taygeta mattr]$ time perl -e '
$max=100000; $c=0; 
open(OUT,">codes"); 
open (IN,"cat /dev/audio | xxd -u -ps -c 5 |cut -b 1-9 |"); 
while (<IN>) { 
  $l++; 
  if(!exists($h{$_})) { 
    $h{$_}=1; $c++; chomp; print "$c\n" unless $c%100;
  }
  if ($c>$max) {
   print "$l lines $c uniques found\n"; close(IN); 
   foreach (keys %h) {print OUT "$_";} close(OUT); exit;}
}' 

...
99800
99900
100000
107849 lines 100001 uniques found

real    0m18.977s
user    0m3.720s
sys     0m0.190s

##</code><code>##

File "codes" contains stuff like (actual data):
C5FF33FF3
FF2F0082F
FFE2FE5AF
6800EF004
99FF35006
20003101A
F3FF7DFFC
FF14FF46F