[Freeswitch-users] Testing iSAC

I have an iSAC client that I'm testing against FreeSwitch. Currently I have my vars.xml with: global_codec_prefs=isac,PCMU,PCMA,GSM,G722 Which works, but only if the client specifies 32kHz mode. I want to test 16kHz mode, but FreeSwitch returns 'not acceptable here', and I can see that when Freeswitch offers iSAC in the SDP it says only isac/32000. So how to enable 16kHz mode for isac? I tried explicitly putting isac@320000h30i, isac@16000h30i into vars.xml, but this simply stops FreeSwitch from accepting anything. Hints gladly received. Regards, Martyn