DTMF Audio filter?

Discussion in 'General Electronics Chat' started by Resist10k, May 7, 2011.

  1. Resist10k

    Thread Starter New Member

    May 7, 2011
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    Im trying ti make a filter to take out dtmf frequencies from my computer ive tried making the simple RC notch and highpass filter but it never seems to work i guess im doing something wrong does anyone know of a filter circuit that will work with a PC
     
  2. marshallf3

    Well-Known Member

    Jul 26, 2010
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  3. Kermit2

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    Feb 5, 2010
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  4. Resist10k

    Thread Starter New Member

    May 7, 2011
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    I'm not looking for an IC to decode DTMF signals or Software, i was trying to Build a circuit to Block the DTMF Frequencies.Possibly a notch or Highpass Filter preferably with just Resistors and capacitors but everything i googled and tried to build hasnt worked too well :(
     
  5. rogs

    Active Member

    Aug 28, 2009
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    What frequencies do you intend to still pass through then?
    DTMF frequencies cover the 'important' part of the audio spectrum, and any simple resistive/capitive 'notch filters,' that block all the DTMF frequencies, are going to block most of the audio band between 300 Hz-2KHz as well.
    To isolate and notch out all the frequencies independently you're going to need pretty sophisticated digital filters, I suspect.
    But why do you want to block them anyway?
     
  6. beenthere

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  7. Resist10k

    Thread Starter New Member

    May 7, 2011
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    i am hooking a dtmf decoder to the sound card to send data out and dont want to be able to hear the tones on certain speakers so i was going to make a filter to block it out. as for the frequenc ranges it seems dtmf is between 697hz and 1.6khz i dont have to block the whole range even if i could notch 3 or 4 frrquencies it would be just fine. my sound card seems to be able to produce a tone the decoder can detect tones just fine coming from computer so i would just need to block 3 or four frequencies to transparently control the decoder
     
  8. Kermit2

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    By resisting the audio 'software' option(which is perfect since you are using a computer) you have made yourself a mountain of a problem out of a simple refusal to consider this solution.

    Making a component based passive filter that will not distort your audio or render it noticeably different from its original form to the human ear is almost an impossibility. Notching a narrow frequency band just doesn't happen 'passively'. It requires complex powered circuitry and even more complex mathematics to design it properly. The best way to accomplish that(if you must do without the software option) is to purchase an already made unit like those used in PRO audio applications such as microphone feedback eliminators
     
  9. Resist10k

    Thread Starter New Member

    May 7, 2011
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    :( id be totally cool with a software solution but i need the dtmf tones to leave the computer so the decoder cant catch them then i wanted to filter them out so they wouldnt come out the external speakers. what would i circuit look like that would use passive components maybe i can fiddle with it so that it is marginally noticable im really not looking for anything that will reproduce high quality audio distortion is ok for now til i can find a better alternative
     
  10. retched

    AAC Fanatic!

    Dec 5, 2009
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    Why not just MUTE the speaker for the duration of the dtmf tone?

    You COuLD use software, if you had 2 sound cards.

    You could run the output of the first through the DTMF encoder/decoder then INTO the second soundcard, filter the unwanted frequencies, then out to the speaker amp, etc....
     
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