[Freeswitch-users] Fax Codecs

[Steve Underwood]

On 01/13/2010 02:20 AM, Joseph L. Casale wrote:
> While faxing is working, I am seeing these in the log when I
> attempt to use rxfax:
>
> switch_ivr_play_say.c:1154 Codec Activated L16 at 8000hz 1 channels 30ms
> switch_core_io.c:652 sofia/internal/1002 at 192.168.13.1 receive message [TRANSCODING_NECESSARY]
>
> So later I see:
> switch_core_codec.c:128 sofia/internal/1002 at 192.168.13.1 Restore previous codec PCMU:0
>
> So I am actually not clear on what's happening? I thought I had the ua set to PCMU but I
> guess fs is seeing the incoming sip session as L16 which I read is bad for fax? What's
> the significance of the last line where it states its restoring the old codec?
>
> Can anyone shed some light on what's actually happening?
>    
A-law and u-law are the right things for the transmission of FAX 
signals, but you can't actually do signal processing on an A-law or 
u-law signal. It needs to be converted to a 16 bit linear signal (i.e. 
L16) for that. What you see is the correct action.

Steve