A Notch Filter Is A What?

SurferJoe46 · #1 06-04-2011, 10:04 AM

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.

lomo · #2 06-04-2011, 10:12 AM

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.

bongomania · #3 06-04-2011, 10:17 AM

Right--basically it's a type of EQ with a very specific purpose: to cut a very narrow band of frequencies.

SurferJoe46 · #4 06-04-2011, 10:26 AM

Right.

I was gonna say that.

Alex1984 · #5 06-04-2011, 11:10 AM

Yeah. Very useful for eliminating feedback. It's like the opposite of a band-pass filter.

SurferJoe46 · #6 06-04-2011, 11:16 AM

Sorta a network?

billfitzmaurice · #7 06-04-2011, 12:04 PM

Quote:

Originally Posted by SurferJoe46

Firstly, my amp has a Notch Filter.

Is it a compressor or a limiter?

Neither, it's a tone control. Google it. Google is your friend.

bongomania · #8 06-04-2011, 12:29 PM

Quote:

Originally Posted by SurferJoe46

Sorta a network?

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.

SurferJoe46 · #9 06-04-2011, 12:33 PM

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.

GrowlerBox · #10 06-04-2011, 12:35 PM

Quote:

Originally Posted by SurferJoe46

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.

You've just decided to buy a fully parametric EQ. Good on you!

SurferJoe46 · #11 06-04-2011, 12:37 PM

I never knew what one of them wuz b4! Thanks.

Bob C · #12 06-04-2011, 12:49 PM

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.

bring the noise · #13 06-04-2011, 01:31 PM

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.

bongomania · #14 06-04-2011, 02:09 PM

If you let us know what part of it is not clear to you, we can help.

billfitzmaurice · #15 06-04-2011, 02:23 PM

Quote:

Originally Posted by Bob C

The notch filter has a very specific and limited function and purpose - to reduce (by a little or a lot) a very narrow frequency.

Not necessarily. If the filter has a Q (width) control the bandwidth can be adjusted.

Quote:

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.

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.

Bob C · #16 06-04-2011, 02:46 PM

Okay, sorry. I stand corrected.

bring the noise · #17 06-04-2011, 03:00 PM

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?

bongomania · #18 06-04-2011, 05:47 PM

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.

billfitzmaurice · #19 06-04-2011, 06:44 PM

Quote:

Originally Posted by bongomania

Sorry Bill, but I have never ever seen a notch filter with anything other than a very narrow bandwidth.

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.

bongomania · #20 06-04-2011, 09:26 PM

Guess we're both splitting hairs here, but still--you are describing a parametric EQ, of which "notch filter" is a small subset.