Hi Babak, you can also try avmd module for a detection of single frequency sound. I have tested avmd on your audio and it detected 425.69 Hz frequency when it's variance threshold was set to 0.0006, 446.23 Hz with default threshold of 0.00025. 2016-04-07 12:32:05.820909 [NOTICE] switch_channel.c:1104 New Channel sofia/internal/1000@192.168.1.27 [4e41e5be-51a0-42fa-87b5-8fde76744530] 2016-04-07 12:32:06.060908 [INFO] mod_dialplan_xml.c:637 Processing beautiful display name <1000>->1705 in context default api avmd 4e41e5be-51a0-42fa-87b5-8fde76744530 start Content-Type: api/response Content-Length: 89 +OK [4e41e5be-51a0-42fa-87b5-8fde76744530] [sofia/internal/ 1000@192.168.1.27] started! 2016-04-07 12:32:12.760908 [INFO] switch_core_media_bug.c:701 Sending early media 2016-04-07 12:32:12.760908 [NOTICE] sofia_media.c:92 Pre-Answer sofia/internal/1000@192.168.1.27! 2016-04-07 12:32:12.760908 [INFO] mod_avmd.c:279 Avmd session initialized, [8000] samples/s 2016-04-07 12:32:12.760908 [INFO] mod_avmd.c:739 Avmd on channel [sofia/internal/1000@192.168.1.27] started! 2016-04-07 12:32:17.480907 [NOTICE] mod_avmd.c:919 <<< AVMD - Beep Detected: f = [425.688780], variance = [0.000533] >>> Avmd works for single frequency tones. Be sure to checkout latest master (this module is yet not of a production quality at this moment). cheers, Piotr