Cutoff Frequencies?

  1. So im making a color organ using my ipod, speakers, splitter, butterworth filters with gain for three seperate frequencies. I want to have a low, mid, and high but I have no idea what the cutoff frequencies for each should be. I know we hear something like a band of 200 Hz to 20 kHz but im totally not sure at all if that would be reasonable to filter an audio signal to seperate bass, treble, and mid sounds. So my question is what cutoff frequencies should i use to adequately filter bass, mid, and treble with each of the three filters im designing?
     
  2. jcsd
  3. gneill

    Staff: Mentor

    You might want to take a look at this vintage article from the 60's:

    "Musette" color organ
     
  4. I'd probably suggest something like

    Bass range: 0 - 120 Hz
    Mid range: 120 Hz - 5 kHz*
    Treble range: 5* - 20 kHz

    * EDIT: On a second thought, I had some doubts; 5 kHz might be too high, maybe 3 or 4 kHz would be better, I'm not sure, I've never built any light organ. But I've done a lot of audio processing and I've built various audiohardware, so I'm probably not completely off :biggrin:.

    The human hearing range is about 20 Hz - 20 kHz (not 200 Hz - 20 kHz) and with some individual variations. You can also google for "instrument frequency chart"; such charts can be helpful. I'm posting an example of such a chart here:

    [​IMG]
     
    Last edited: Sep 2, 2013
  5. An interesting way to play with it is to install a graphic equalizer app and play with the frequency ranges. You can sorta try to visualize sound vs light. Has drawbacks, but helps you to understand the frequency characteristics of the stuff you listen to.
     
  6. jim hardy

    jim hardy 5,016
    Science Advisor
    Gold Member
    2014 Award

  7. That is an excellent suggestion. :thumbs:

    EDIT: try an equalizer which shows the spectrum, like e.g.:

    [​IMG]

    (I will give you some suggestions on free software, gotta check my resources, I'll be back soon...)
     
    Last edited: Sep 3, 2013
  8. Some software suggestions:

    1. In the Winamp media player, there is a built-in equalizer and a spectrum (but the spectrum window is pretty small, though).
    2. Free spectrum analyzers can be found here.
    3. Free equalizers can be found here.
    Regarding point 2 and 3 I'm not sure if the list contains only VST plugins (which need an audio software host) or also includes stand-alone software. I would personally try this: Voxengo SPAN (it's a free plugin). I haven't tried that particular plugin, but I have tried other Voxengo software, and they are pretty good.

    Maybe someone else here has a suggestion on a stand-alone equalizer/spectrum analyzer.
     
  9. Winamp is OK because you can change it while listening. The spectrum window sucks though (shows clipping when there is none, and it always shows the input spectrum, not the results after EQ.)

    Third octave equalizers are the best since the position of the sliders are a good representation of the actual frequency response. The final curves with winamp won't really be the slider positions (close enough for getting a feel though)
     
  10. those are some awesome suggestions. thank you very much
     
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