[Freeswitch-users] inband DTMF detection and drop

SamyGo govoiper at gmail.com
Wed May 13 17:23:26 UTC 2020

Hi all,
I've followed all the previous suggestions to detect the inband DTMF coming
from a provider and to drop them from going further into B leg. However the
inband DTMF still goes to otherside and user can hear clicking sounds.
Here's what I've  done so far:

FreeSWITCH Version 1.10.2-release+git~20191231T140119Z~f7bdd3845a~64bit
(git f7bdd38 2019-12-31 14:01:19Z 64bit)

*OS:* Ubuntu 18.04.4 LTS

<extension name="dtmf_filter">
            <condition field="${acl(${network_addr} lan)}"
            <condition field="destination_number" expression="(.*)">
                        <action application="set"
                        <action application="set"
                        <action application="set"
                        <action application="set" data="dtmf_verbose=true"/>
                        <action application="set" data="drop_dtmf=true"/>
                        <action application="spandsp_start_dtmf"/>
                        <action application="bridge"

I've also tried suggestion by other users on mailing list related to flush
JB on DTMF rtp_bug but that doesnt help either.

*CONSOLE OUTPUT:*2020-05-12 23:59:10.195999 [DEBUG] mod_spandsp_fax.c:295
FLOW DTMF Potentially '5' - total -15.55dB, row -32.25dB, col -40.30dB,
duration 338436 - miss
2020-05-12 23:59:10.195999 [DEBUG] mod_spandsp_fax.c:295 FLOW DTMF
Potentially '5' - total -17.99dB, row -30.58dB, col -40.99dB, duration
338538 - miss

It does detect the number but its not a hit.

Can I get some more ideas how to drop inband DTMF tones, Thanks.

Best Regards,
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