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A Notch Filter Is A What?

Discussion in 'Amps and Cabs [BG]' started by SurferJoe46, Jun 4, 2011.


  1. Firstly, my amp has a Notch Filter.

    Is it a compressor or a limiter?

    I lean toward limiter - but I'm not 100% convinced I know that for sure.
     
  2. lomo

    lomo passionate hack Supporting Member

    Apr 15, 2006
    Montreal
    A notch filter is a device that can remove/attenuate a narrow freq range. It's designed to "surgically" lower a freq that is causing problems, without taking out a broad spectrum. An eg is specific frequencies causing boom or feedback.
     
  3. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Right--basically it's a type of EQ with a very specific purpose: to cut a very narrow band of frequencies.
     
  4. Right.



    I was gonna say that. :ninja:
     
  5. Alex1984

    Alex1984

    Jan 16, 2010
    Vancouver
    Yeah. Very useful for eliminating feedback. It's like the opposite of a band-pass filter.
     
  6. Sorta a network?
     
  7. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Neither, it's a tone control. Google it. Google is your friend.
     
  8. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    There have been a couple of instances where an amp company used the word "network" to describe some amp feature, but generally speaking the word "network" does not apply here. It's a cut-only EQ, period.
     
  9. So Bill - I took your advice and as I see it from a Google reference, the Q-factor is set and that a HIGH Q-factor is not wanted, whereas a MODIFIED or lesser Q-Factor is wanted more-so for our purposes - right?

    Begs a new question then:

    ........ why isn't the Q-Factor adjustable? Kinda like changing the aperture of a camera, this would seem to be a necessary factor for a Notch Filter to work better/correctly.

    Seems to me that any chosen Notched Frequency zone then also the width of that zone (Q-Factor) would be just as important to get the best control of offending/booming frequencies.
     
  10. GrowlerBox

    GrowlerBox

    Feb 10, 2010
    Nude Zealand
    You've just decided to buy a fully parametric EQ. Good on you!
     
  11. I never knew what one of them wuz b4! Thanks.
     
  12. Bob C

    Bob C

    Mar 26, 2000
    Duluth, MN
    The notch filter has a very specific and limited function and purpose - to reduce (by a little or a lot) a very narrow frequency. Other types of EQ's will do other things that you may want or need.
     
  13. bring the noise

    bring the noise

    May 18, 2011
    The acoustic users manual says It's a active -10db notch for freqs between 50hz-1000hz. 12 o'clock on the freq knob is at approximately 250 Hz. I don't really understand it.
     
  14. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    If you let us know what part of it is not clear to you, we can help.
     
  15. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Not necessarily. If the filter has a Q (width) control the bandwidth can be adjusted.

    Read this, specifically the section on bandpass filters, though all of it should be second nature:
    Signal Processing Fundamentals

    A notch filter is a bandpass filter that can only cut, not boost.
     
  16. Bob C

    Bob C

    Mar 26, 2000
    Duluth, MN
    Okay, sorry. I stand corrected.
     
  17. bring the noise

    bring the noise

    May 18, 2011
    I guess I understand what it does, just why wouldn't you cut the freq on the eq. So whatever freq is selected is always cut at -10db?
     
  18. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Because the EQ on an amp is typically very wide-band, meaning if you turn down a knob labeled "500 Hz", you are also turning down everything from (for one example) around 100 Hz to 900 Hz, in a bell-shaped curve. The width of the range of different frequencies affected is described by the "bandwidth" or "quality" (Q).

    A notch filter is designed to cut a narrow bandwidth, a "notch" in the frequencies, rather than a broad bell shape. Sorry Bill, but I have never ever seen a notch filter with anything other than a very narrow bandwidth. Give it a wider band and it's a cut-only EQ, but not a notch filter.
     
  19. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    It's simply a matter of using the extra knob and other components required. For the same reason this example seems to have a fixed cut rather than variable. The physical difference between a narrow bandwidth notch filter and a wide bandwidth midrange cut filter can be as simple as a single resistor value.
     
  20. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Guess we're both splitting hairs here, but still--you are describing a parametric EQ, of which "notch filter" is a small subset.
     

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