Sound to light. Adapting the Chemelec light organ

Discussion in 'The Projects Forum' started by Fenris, Aug 17, 2009.

  1. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    Hi Guys

    I was browsing the web, as you do, when I cam upon this 'light organ' circuit. Now I have a particular use for this and with that in mind I have chopped the circuit up a bit. I only require one driver section.

    Now as I only need 2 parts of an LM324 I could simply substitute another op-amp couldn't I? So long as it is OK on 12VDC.

    The mosfet shown was a single but in another circuit I have it has 2 in parallel so I will do the same and use the IRF540 which I have plenty of rather than the one suggested. The Bulbs will be 2off 12V/24W wired in parallel.

    The input will be from an LM358 pre-amp and electret mic to drive this light organ. Other than what I have asked it looks fairly straight forward. My only other question is -

    Where does the human voice fit as far as frequency range goes when looking at high pass, low pass, and Bandpass. Which one would best serve the vocal input?

    Thanks in advance

    regards

    Fenris
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    The telcos got by with a range of about 300 - 3000 Hz. That's a bit restricted, but most of the important vocal noise is in there.
     
  3. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    The telecom does a fair play, but i've seen that human voice goes till a bit more than 4kHz.
     
  4. bertus

    Administrator

    Apr 5, 2008
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  5. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The harmonics of vowels go to 4khz but the important consonants go up to 14kHz.
    Polycom make speakerphones that use two telephone lines for 7kHz response instead of the muffled 3.4kHz response of a single phone line.
    Then you clearly hear the difference between "faucet" and "soffet".
    You hear the big difference between "failing" and "sailing".
    On an ordinary phone call the words failing and sailing both sound like "ailing".

    Polycom lists 24 small words that all sound the same on an ordinary telephone call.

    When I worked with boardroom tele-conferencing systems I made an equalizer that boosted 3.4kHz +10dB (don't tell Bell) so that voices were much clearer. Everywhere I demo'd, my demo unit was sold.

    http://www.polycom.com/global/docum..._of_bandwidth_on_speech_intelligibility_2.pdf
     
  6. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    Hi Chaps thanks for the input. Perhaps I should have been a little more precise in what I was asking about the frequency range.

    I gather that the 3 different filters work by the RC network which sets what each filter lets through and stops. I have just tried doing the math following an online wiki but as is usual my maths sucks.

    So which setup of the three would let more of the human voice through so that the lights react accordingly.

    Also am I correct in my assumption that I can just slip any old op-amp in place due to the fact that I only need 2 of the 4 parts of the original LM324, a 14 Pin package. So an op-amp with only 2 parts, an 8 Pin package, would be fine.

    regards

    Fenris
     
  7. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    The TL072 or TL082 are well known dual Fet opamps.
    If you want rail to rail capability check the OPA284.
    See the datasheets for more details.

    Greetings,
    Bertus
     
  8. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    Cheers Bertus

    I am only going single rail supply so the TL072 will be fine. I already have the PCB Drawn up and ready to role.........although if I have selected the wrong filter that will cause problems :D.

    regards

    Fenris
     
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