Getting DD Sound On TS & Not On Airtel

Hi Friends

I have Samsung Full HD Led F5500. From manual shows that it has the capability of Dolby Digital Sound option.

Recently my Airtel HD box got updated will new changes of Dolby Digital Sound through Hdmi. When i activated "Dolby Digtal Sound" option from my Airtel box then no audio came on all HD channels.

On same settings my Tatasky HD + box is giving Dolby Digital sound through Hdmi.

Now i am fully puzzled that which gadget have problem, Samsung or Airtel?

Please guide me