DTMF decoding in noisy environment

7 thoughts on “DTMF decoding in noisy environment

  1. I am using DTMF decoder on GL865-DUAL, but when the line is opened, ambient sound (radio), generates false DTMF tones (that are not sent using keypad).

    How can reject that. One possibility is by AT#DTMFCFG command, so any suggestions about scaling and threshold values? Thanks!

      1. Far end is my GSM headset that is close to loudspeaker. It is the source of noise. Module microphone is muted.

          1. GSM moblile is close to the speaker of my laptop that is playing internet radio and this sound is generating wrong DTMF codes in the module side.

          2. This is the first time we have a similar feedback from a customer
            Regarding DTMF decoder. Also we never observed a noise which can cause a false
            DTMF on module. 
            Meanwhile you can try to improve the threshold step by step (step of 100 every time)
            to see how this change improve the performance of the decoder( don’t exceed the value of 5000).

            It can be interesting to have, if possible, a wave file recorded
            At module output to analyze it; if this is possible, please send the file to TS-EMEA@telit.com.

          3. The problem is not with me but with our customer that is testing device.

            DTMF decoder is working great, taking in mind that so noisy envoronment is not typical during voice conversations. Especially sending music via audio channel could result false DTMF decoding – vusic as well voice spectra are in the same band as DTMF tones.

            We solve the problem by decoding double tones – double push 1or 2 or … till # and *.


            Btw, last month I had a problem with our GSM operator Globul. They reject sending DTMF tones within their network.It was impossible to send DTMF between two phones with Globul SIM card, but sending?receiving fro other operator was possible (MTEL->GLOBUL and GLOBUL->MTEL). I asked them to repair this and now everything is OK.