In an audio recording (say a telephone conv. b/w two people), how would I programatically detect and remove the dial-tone at the beginning of a call using python. Ex : sample audio call As you can see the first 15 seconds or so is just a dial tone like tring-tring-tring-tring.

Are there any audio analysis libraries in python that could help me achieve this?

If this is not the right forum, kindly point me to the right place.

  • 1
    $\begingroup$ unless your country's telephones work extremely different then my country's ones, then "tring" is not a dial tone, but a ring tone? Also, what about simply detecting the crossing of an amplitude threshold? This looks extremely much like "amplitude higher than 0.7 for more than a millisecond" is a reliable detector. $\endgroup$ Nov 17, 2017 at 8:09
  • $\begingroup$ Ok thank you for correcting me. ringtone/hold music/ivrs was what I meant. the tring tring part. could you please point me to any python libraries please. thank you. $\endgroup$
    – kRazzy R
    Nov 17, 2017 at 19:41
  • $\begingroup$ . OK, updating my question. But you got it right, I just want to `detect parts of the call which has automated IVRS, or hold music or the tring tring $\endgroup$
    – kRazzy R
    Nov 17, 2017 at 20:24
  • $\begingroup$ @MarcusMüller Could you pleae tell me how to go about "amplitude higher than 0.7 for more than a millisecond detection method $\endgroup$
    – kRazzy R
    Dec 5, 2017 at 19:08
  • $\begingroup$ I'm afraid I don't know where to start if you don't know what "amplitude" means in the context of a digital signal. $\endgroup$ Dec 5, 2017 at 19:42

1 Answer 1


You can use librosa and scikit-learn to create a machine learning classifier. It would work roughly like this:


  1. Get training signals of (A) just phone ringing, and (B) no phone ringing, e.g. ordinary conversation.
  2. Segment the training signals with a frame size of ~50-500 milliseconds.
  3. Extract features from each frame, e.g. MFCCs.
  4. Train a scikit-learn classifier, e.g.

    classifier.fit(X, y)

    where X is a ndarray of feature vectors, and y are the target labels, e.g. "ring" (1) and "no ring" (0).



where X is an ndarray of feature vectors extracted in the same way from a test signal.

The latest frame which returns a positive "ring" label is where to truncate the signal.

  • $\begingroup$ by Segment the training signals with a frame size of ~50-500 milliseconds do you mean splitting the whole audio into pieces of 50milliseconds each? Or do you mean for it to be the sliding window frame size. $\endgroup$
    – kRazzy R
    Dec 5, 2017 at 22:54
  • $\begingroup$ Do you have example for such sets to train and observe the results? $\endgroup$
    – Mark
    Apr 19, 2021 at 6:52

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