\x00 is null
\x01 is ^A
\x02 is ^B
\x03 is ^C
...
for chars grater than \x7F
\x81 is ~A
\x82 is ~B
\x83 is ~C
...

^char can be input as ctrl-v ctrl-char, i.e., ^A is ctrl-v ctrl-a

when ctrl-char has real meaning, like ^T or chars greater than x7f,

echo abc | sed s/a/\\x01/ | sed s/b/\\x02/ |sed s/c/\\x03/ > ctrls1.txt

echo abc | sed s/a/\\x81/ | sed s/b/\\x82/ |sed s/c/\\x83/ > ctrls2.txt