[Freeswitch-users] fax tone detection failed

[Kristian Kielhofner]

This would be awesome because (as you say) you can't count on the
receiving machine sending the 2100Hz tone...

On Thu, Apr 14, 2011 at 1:58 PM, Steve Underwood <steveu at coppice.org> wrote:
> On 04/15/2011 01:32 AM, Christopher Rienzo wrote:
>> 2100 Hz is the ANS tone from the receiving side of the fax call.
>> That's what I detect on my outbound calls.
> An answering machine sends 2100Hz, but its very unreliable to rely on
> hearing it. In spandsp there is a module which does a much more thorough
> job of detecting a FAX machine. It will accept the V.21 preamble, which
> normally follows the 2100Hz tone, as a substitute for the 2100Hz itself.
> That way a call which starts passing audio a bit late (which they often
> do) still results in proper FAX detection. We need to expose that
> functionality in FreeSwitch, but have not done so yet.
>
> Steve

-- 
Kristian Kielhofner