I'm a ten-letter word, but when I am heard,
It is a surprise, but I'm half that size.

My first sound is found when half isn't around.
When a pair is amiss, the other is called this.

The second has one where normally two form a pair.
You will get the nod if you look in a pod.

Together, my fifth and third hold music that is heard.
A pair you are seeking, alphabetically speaking.

And the fourth sound, it will be found
If you look where I send, in the middle of end.

What word am I?