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EQ and shelving, explanation please

Discussion in 'Amps and Cabs [BG]' started by the low one, Sep 16, 2008.

  1. the low one

    the low one

    Feb 21, 2002
    I understand EQ and frequencies but what about shelving? On my Trace Elliot amp and MXR M80 when I read what the frequencies are for the bass, mid and treble it says shelving after the numbers, but what does “shelving” mean? Does it mean for example that by moving the bass knob up, and it’s voiced at 60 HZ say, that it doesn’t just affect the 60 HZ frequency but other frequencies around it as well to create a sort of EQ curve, or does it mean something else?
  2. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Shelving EQ affects the corner frequency and everything below it on bass, everything above it on treble. Peaking EQ peaks at a single frequency.
  3. Mcrelly


    Jun 16, 2003
    Minnesota, USA
    on a non shelving eq imagine a grading curve from school. lets say you boost 500hz 10db. 500 would be increased the most. the frequencies on either side of 500, say 400 and 600 will also be boosted a little less than 500. 300 and 700 a little less still. eq circuits have a width of affected frequencies designed into them. this is called the "Q" its usually a fixed range of frequencies on either side of the targe frequency.

    I'm not using proper terminology for all this because I don't know all the terms.

    shelving is usually used on lower frequency, maybe under 100hz and hhigh frequencies like 10k,15k etc depending on what the EQ is used for. I could imagine a bass eq might "shelve" closer to 10k, I'm guessing. now remember the "curve" I talked about? imagine at the top of the curve just continuing straight over to the lowest or highest frequency extreme. lets say you boost a shelving eq at 100hz 10db. it will boost 90hz 10db, 80 10db...etc while 110hz will be a little less than 10db and 120 a little less again

    understand? hope that helps...
  4. bongomania

    bongomania Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Low shelving cuts or boosts everything below the frequency you set. High shelving cuts/boosts everything above the frequency you set.
  5. jokerjkny


    Jan 19, 2002
    NY / NJ / PHL

    rather, every frequency below the 60Hz will be boosted up. i.e. 60hz, 50Hz, 40Hz and so on, will be boosted. literally like taking a real life shelf and moving up all those frequency sliders at once!

    high frequency shelves work in the same manner, but affect all the frequencies above it. i.e. on a 4kHz shelf, if you cut/boost that knob, all the freq's above 4kHz, 5kHz, 6kHz, and so on, can be cut/boosted at will.
    Larchi likes this.
  6. the low one

    the low one

    Feb 21, 2002
    Thanks everyone, I'm never to old to learn something new.
  7. One of those things I always thought I knew the answer to ..... but didn't.
  8. manchild


    Jan 30, 2008
    I know some EQ systems can alter how much the Q effects the frequencies surrounding the centre frequency.

    On systems where this is fixed how much of the surrounding frequencies are effected when you boost a particular point. For example if you were to boost 500hz by 6db at what point either side would the Q stopp effecting the range? Is there an industry standard or does it just differ between brands/models?

  9. will33


    May 22, 2006
    6 year resurrection.....not bad. :D

    Hat you're describing is the Q. That's how wide of a band of frequencies get affected on either side of the center frequency you've chosen.

    1 or 1-1/3 octaves seems to be fairly common in a lot of bass amps with frequency sweeps. Those are the "semi-parametric" eq's you see on some amps. They let you chose the center frequency, but the Q is still fixed. A parametric eq ( not semi ) lets you adjust the Q as well from very narrow to very wide. Don't see too many of those built into bass amps, maybe a couple models here or there. Most parametrics are built as outboard gear, or in programmable DSP systems.
  10. AlexanderB


    Feb 25, 2007
    To make things more complicated, some manufacturers also make "quasi-parametric" equalizers, such as in my EBS 1V2. In this case it is a sweepable, "boost only" equalizer where Q is affected by how much boost you add to the signal. For additional confusion, the mid range control also has a three position switch to set the Q-range; wide, normal and narrow.
    Seems very complex in text, but is pretty intuitive to work with and sounds very "musical" (I do not really like that expression but you might get the drift) in most settings.
  11. spz8


    Jan 19, 2009
    Glen Cove, NY
    I just noticed this is a resurrected thread, but since it's up and running, just why would you want a shelving type of EQ - e.g.: low shelving at 60hz? Maybe I want 120hz down to 60hz a little boosted, but certainly don't want 30hz boosted. This type of EQ doesn't sound very useful. Am I missing something?
  12. AlexanderB


    Feb 25, 2007
    I guess that is one argument for the above EBS equalizer - the shape of the boost is depending on how much you crank it. It "sort of" (not exactly) goes from shelving to bell shaped as you crank the knob.
  13. Most amps do have a highpass filter on the input stage, so nothing below 25 - 30 Hz is coming in too strong anyway.

    Many low mid controls do, in fact, go down to 100 - 120 - 150 to allow for the kind of adjustments you want to make. Very few shelving controls are voiced to start as high as 120, I would think that would be on a budget combo amp perhaps, where there would be high-passing on the input.
  14. AlexanderB


    Feb 25, 2007
  15. Lowbrow

    Lowbrow Supporting Member

    Apr 22, 2008
    Pittsburgh PA!
    I had a Peavey TNT in the '80s that in addition to the usual bass, treble and mid knobs has these mysterious ones called 'frequency' and 'bandwidth.' Nobody in the group could figure out what they were supposed to do. The running joke became that bandwidth would determine how closely together the band members had to stand and by cranking the frequency we'd get more gigs.
    Larchi likes this.
  16. Blankandson

    Blankandson Supporting Member

    Oct 20, 2010
    Gallatin, Tennessee
    If you actually enjoy learning about all the filters out there become a ham radio operator. You get to use or ignore a lot more of them. My ICOM had 'notch filters' in three widths. I could transmit with a keyer on a tiny piece of a huge bandwidth, and anyone just a tad on either side of me wouldn't be heard (by me). When you're chatting with someone in Brazil it make the conversation much more enjoyable. Fun stuff for more than just music.
    And I was wondering why BFM suddenly showed up! I miss the guy.
  17. Jim C

    Jim C Is that what you meant to play or is this jazz? Supporting Member

    Nov 29, 2008
    Bethesda, MD
    I thought for the OP.
    Not all filters / EQ sections are created equal
    One trick with semi-parametric equalizers is to pick a key frequency in the middle of the spectrum and cut and boost it severely.
    Some of the less expensive designs can often ring like a fire alarm with a lot of boost with a tight octave setting when others may sound more musical.

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