Sound of Fitness

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?

Check Braingle.com for the answer.