When do cockerels start to crow properly?

[clyvelovestuna]

Just out of curiosity lol!
My cockerel about a year old and a couple of months old now, and his crowing sounds funny. Its more of an e-eeer-eerrrr than a cock-a-doodle-doo.
Is this normal? is the latter just a stereotype within chickens or will his crow slowly develop into that sound?

 

[Callender Girl]

My Cochin Bantam rooster started crowing when he was about three months old, and the sound was much like what you've described. He's about eight months old now, and although he doesn't have the volume of my mature Iowa Blue rooster, Billie Boy now produces a genuine cock-a-doodle-doo.