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LPF vs. Shelving -dB treble EQ

Discussion in 'Effects [BG]' started by Nyarlathotep, Apr 19, 2009.


  1. Nyarlathotep

    Nyarlathotep Banned

    Feb 5, 2006
    West Coast of Canada
  2. rcubed

    rcubed

    May 8, 2008
    Vista, CA
  3. dannybuoy

    dannybuoy

    Aug 3, 2005
    England
    LPF's tend to have a steep dropoff at the selected frequency. The further up you go past the cutoff frequency, the steeper the rolloff, on a graph it would look like a cliff edge. Shelving EQs (if set to cut and not boost) will have a similar rolloff up to a point but will then plateau out so that all fequencies above that point will be reduced by the same amount of dB. On a graph it'll look like a straight line, or a shelf.
     
  4. slyjoe

    slyjoe Supporting Member

    Jun 28, 2008
    Valley of the Sun (AZ)
  5. Nyarlathotep

    Nyarlathotep Banned

    Feb 5, 2006
    West Coast of Canada
    Interesting..... So you can change the resistor or the cap.... *evil laugh*

    Thank you very much :D

    quick edit: I noticed that its for a 6db/oct filter. Any sites for stuff higher, like 15 or 30+?

    I'd look it up myself, but I gotta go to work. And tomorrows 4:20......
     
  6. slyjoe

    slyjoe Supporting Member

    Jun 28, 2008
    Valley of the Sun (AZ)
    The muzique site linked shows a low pass and high pass PASSIVE filter. And they are NOT the circuit used in instruments due to the interaction with other elements such as volume controls and coils in the pickups.

    15 or 30 dB high and low pass filters are going to take a lot more components - it seemed from the original post you were looking at active???
     
  7. dannybuoy

    dannybuoy

    Aug 3, 2005
    England
    Most basses have a passive LPF built into them - that's basically what your tone control is!
     
  8. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    I was just about to say...does nobody use knobs anymore? ;)

    Last night I had a gig where I thought I was too trebly...turned down the tone knob on the bass about 1/3...perfect!
     
  9. slyjoe

    slyjoe Supporting Member

    Jun 28, 2008
    Valley of the Sun (AZ)
    The tone control in a passive bass functions as a low pass filter (with some nuances) as danny and jimmy said, but the circuit is not configured as a LPF as illustrated at the muzique site.

    The LPF shown has a series resistor with a shunt capacitor. Tone circuits in instruments have a resistor (variable) in series with a capacitor; they are both shunted across the output. The only time they are equivalent is when the resistance = 0.

    Put that LPF circuit in your bass and you will get a much different response than a typical tone control you are familiar with.
     
  10. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    It isn't going to make a lick of difference to me when playing "Blue Moon" ;)
     
  11. slyjoe

    slyjoe Supporting Member

    Jun 28, 2008
    Valley of the Sun (AZ)
    HAH - you're right. :p Unless you're putting that circuit into your bass.
     
  12. Nyarlathotep

    Nyarlathotep Banned

    Feb 5, 2006
    West Coast of Canada
    Sorry for not replying yesturday (the earliest I could get on after you posted).... but it was 420....

    Anyways, yes Im looking for a schem for an adjustable freq sharp slope LPF. Im guessing thats active :oops:

    There was a schem for a 36dB/oct LPF @ 1Khz in the PDF I linked. Im wondering what resistors I could switch out for pots, or resistor+pots, to get a range of freqs on it. Im thinking something like 20-2000Hz for the corner freq.
     
  13. HogieWan

    HogieWan

    Feb 4, 2008
    Lafayette, LA
    LPFs cut out everything above the selected frequency (after a somewhat steep dropoff), but a shelf cuts (or boosts) everything above that freq equally. Think hill vs plateau.
     
  14. Doner Designs

    Doner Designs Steve Doner Gold Supporting Member

    Jun 2, 2012
    Metro Chicago Area
    Doner Designs is an alias for Steve Doner
    I came to this thread because I had the same question but just realized I know the answer (I think) and do not see it covered here very clearly.

    It's been awhile since I have raised a zombie from the dead, so here goes:

    A treble shelving control on an amp or bass works by boosting or cutting everything above a certain fixed frequency. The knob controls the amount of boost/cut.

    A typical LPF, similar to the VLE control on Markbass amps or the LPF/HPF box made by Broughton audio aggressively rolls off all frequencies above a certain frequency. The knob controls the cutoff frequency.

    Maybe I'll remember this now that I have written it down. :) Context is that I'm debating myself about whether or not to sell my Broughton LPF/HPF, my Empress ParaEq, both or neither. :)
     
    Last edited: Jun 5, 2017
  15. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    I love it when old threads come back to haunt me. A Broughton LPF and HPF are now mounted on my board and it's not the same as turning down the tone knob on my bass :D
     
    Doner Designs likes this.

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