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DTMF and Pulse Dialing

I had promised before that I would write about DTMF and pulse dialing in future. Finally I have decided to write about them!

This article may be ignored by IVR professionals as they must be quite bored with these two terminologies! But many users who have to listen to announcements like “If you are in pulse mode, then please come to Tone mode by pressing # ( Hash), thank you”, for them it might be useful!

Many telephone Instruments/Telephone Handsets has a button on either bottom-side of it or side of it which says P And T on either side. It means Pulse or Tone. Depending on the position of that button, your telephone instrument will generate either pulses or DTMF tones on pressing a key on the keypad.

DTMF stands for Dual Tone Multiple Frequency.  It esentially used to depict the 4X4 Matrix keypad used for Telephone Keypad. 1,2,3,4,5,6,7,8,9,*,0,#,A,B,C,D. Many telephone instruments don’t have A B C D keys! DTMF constitutes two frequencies which are combined together for denoting a DTMF digit.

Here is the table :

1209 Hz

1336 Hz























This tables shows that:

When you press Key 1, it generates two frequencies, 1209Hz and 697Hz.  Now, lets unsrstand the telephone operation

It has two state or situation

Connecting state : Here you lift the phone, hear the dial tone, and press the number you want to dial. And wait for either ring back tone or some busy tone! This state can be called connecting state. In this state, when you press the keys, these keys ( the two frequencies ) are transmitted to the exchange. Exchnage in turns try to connect to the number you have dialed.


Connected State : In this state, call is connected and you are talking to your friends ( girfriends), relatives, business contacts or IVRS! Now if you press a key, it will still produce the same two frequencies and it will be heard by you as well as the person at other end which can be IVRS too! That is how DTMF is used for selectiing various options in IVRS! The tone duration has minimum period to detect and I think its 40ms ON and 80ms OFF. it means it has to generate the tones for minimum period of 40ms for the other end to detect and minimum 80ms of gap for the next DTMF tone!

TIP : If you a smart person, you can use the above information this way!

Suppose you have a landline phone in your house. And your father has put a lock on the keypads so that you can not make any outgoing calls! But you can still make outgoing calls! All you have to do is, using your mobile phone, press the keys of the number you want to call, and then record those tones! ( How do you do it, I wont tell!) Just record those tones, lift the handset, play the recorded tones in front of the mouthpiece of handset and wow, you made a call to that number! I hope I wont be sued for this piece of information!

If the Telephone handset is in Pulse Mode, then when you press a key, it will connect / disconnect corresponding to the number of the key! Suppose, you press a 1, it will disconnect once and then connect again! You can think this as ON HOOK and OFF HOOK! This cycle is for certain duration and the duration is standardized. Its called Break and Connect too.

In connected state too, you can press keys in pulse dialing! It will produce some sound which corresponds to some frequency only! And if IVR can detect that frequency, IVR can detect pulse dialing too in connection state and IVR will stop asking you to come to Tone mode! But most IVR Systems dont support this!

Last information : Mobile Phones dont have Pulse dialing option.

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{ 7 comments… add one }
  • Nirmal February 28, 2009, 2:12 am

    Excellent! Specially the tip! I never thought one can make calls without pressing keys!

    Thank you very much for the informative article.

  • Siavash May 24, 2010, 1:48 pm

    really nice, i need this information…

  • Nadia Raza August 19, 2010, 2:08 pm

    Mind blowing info, simply amazing & above all easy to understand . that TIP will remain in my mind for the rest of my life 🙂

  • Uttam Pegu August 19, 2010, 4:19 pm

    Hi Nadia,
    Thank you for the feedback!

    I have made many calls using the TIP when I was in college! You bet, not only from the phone at our home!

  • Ankit November 13, 2010, 7:28 am

    wow the tip seems to be the useful one…

  • dave April 16, 2013, 2:17 am

    Article provided some useful information but was hard to read with all the spelling and grammatical errors.

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