SIP Trunk different audio IP

My provider is sending me 2 VLAN, one with data and the other with a SIP Trunk.
I was told the audio ip and the signaling IP for Trunk Connection, no user or password is needed because it is configured in the fiber circuit.
The question is, how do I configure a SIP Trunk with the Signaling IP different from the Audio IP. When I put the signaling IP in the host parameter of the sip trunk I can make calls but no audio is passing.
Thanks in advanced for the help.

Use media_address

[quote]; The IP address used for media (audio, video, and text) in the SDP can also be overridden by using
; the media_address configuration option. This is only applicable to the general section and
; can not be set per-user or per-peer.
; Note that this does not change the listen address for RTP, it only changes the
; advertised address in the SDP. The Asterisk RTP engine will still listen on
; the standard IP address.
; media_address =[/quote]