Shelving equalizer and frequencies

[RuudNL]

At the risk of asking an extremely stupid question, here it is...
How is the frequency (on the faceplate of a shelving equalizer) defined?
Is it the frequency where the maximum boost/cut occurs? (As indicated near the boost/cut knob.)
Or is it a 3 dB value from 'flat'?
Or is it something half way?...
I am asking this because I developed a good sounding equalizer with variable frequencies, but I would like to mark the frequency selector as is standard with this type of equalizer.
I am sure the EQ 'pros' know the answer!
Many thanks in advance.

This example shows frequency responses marked as: 33, 56, 100, 180 and 330 Hz.

 

[JohnRoberts]

I don't recall ever seeing an official definition. I would speculate half power (-3 dB), measured at full boost.

JR

 

[ruffrecords]

I am not aware of an accepted definition. Don't forget there are two turnover frequencies associated with a shelving EQ; the one where boost/cut starts and the one where it starts to flatten out. They are often a decade apart. I suspect most end users would expect it to mean the frequency at which the response effectively flattens out.

I do not design, build or use shelving EQs any more. Who needs boost extending beyond 20KHz or below 20Hz? Instead I design/use low Q peaking EQs (Q ~ 0.5). These have a similar response to shelving EQs but they have no out of band boost.

Cheers

Ian

 

[JohnRoberts]

I am not aware of an accepted definition. Don't forget there are two turnover frequencies associated with a shelving EQ; the one where boost/cut starts and the one where it starts to flatten out. They are often a decade apart. I suspect most end users would expect it to mean the frequency at which the response effectively flattens out.

I do not design, build or use shelving EQs any more. Who needs boost extending beyond 20KHz or below 20Hz? Instead I design/use low Q peaking EQs (Q ~ 0.5). These have a similar response to shelving EQs but they have no out of band boost.

Cheers

Ian

Bass and treble shelving EQ were very popular, cheap and easy general purpose (one op amp section) EQs.

One circuit trick that I used back in the day was to add a capacitor in series with the input to the LF boost/cut leg. Properly sized the RC could be tuned to deliver full 20Hz response while commanding cut, but effect a rising HPF pole that scaled higher frequency for larger amounts of LF boost commanded. This neatly avoids excessive LF boost, while delivering full LF cut.

JR

 

[Newmarket]

I would think that the frequency stated would be the "3dB frequency" as that is generally regarded as the "Turnover Frequency" Fc of such a filter.

 

[john12ax7]

There is no real standard. Anywhere from 1dB to 3dB or more below max boost is seen in commercial designs. Some will even use the midpoint turnover frequency.

 

[zamproject]

Neither I know any standard ?!?
Don't know if it help, but my daily use reference is an old 70' desk, where the boost/cut value (stepped) is exactly what the plot show at the announced (and fixed) frequency.
So the 80Hz shelve cut 6dB@80 when selector is @ -6dB

Meaning that in your implementation, for e.g. the -100Hz- frequency plot, with a 10dB boost (or cut) knob label point, the frequency knob point @ 400Hz
Or another one, if you set Hz@label 200 and boost/cut @label 10, you get your 56Hz plot

This is probably far from actual electrical/mathematical Fc corner at filter, but as operator it's easy to mentalize.
What you see on knobs -freq- and -gain- is what you get, at this point. Any decent sound engineer is well aware that overall shelve EQ shape start way before and finish far away from that point.

This may be challenged at extreme setting...but this is extreme setting, and then, when at mix you decide to be on the edge of a setting you no longer look for numbers on a knob

 

[john12ax7]

Another approach is if you have switchable bell and shelf, the bell frequency is well defined. Make the shelf look similar to the bell just extended in one direction.

 

[Madman]

At the risk of asking an extremely stupid question, here it is...
How is the frequency (on the faceplate of a shelving equalizer) defined?
Is it the frequency where the maximum boost/cut occurs? (As indicated near the boost/cut knob.)
Or is it a 3 dB value from 'flat'?
Or is it something half way?...
I am asking this because I developed a good sounding equalizer with variable frequencies, but I would like to mark the frequency selector as is standard with this type of equalizer.
I am sure the EQ 'pros' know the answer!
Many thanks in advance.

This example shows frequency responses marked as: 33, 56, 100, 180 and 330 Hz.

Normally the Freuqency of an Shelving EQ is defined at half gain, in your frequency response for example the red one is 200 Hz.

 

[MagnetoSound]

Does the Heritage LF shelf really start at 20kHz??

 

[RuudNL]

Does the Heritage LF shelf really start at 20kHz??

These are measured frequency responses on an equalizer with frequencies specified as: 33, 56, 100, 180 and 330 Hz.
So the one you marked in red is supposed to be the '56 Hz.'

 

[MagnetoSound]

Looks like the 3dB point on the 180 curve happens at ~2k

That’s low Q!

 

[Madman]

additional for those who want to know it in detail heres a mathematical derivation of a low shelf EQ

LowShelf: H(s) = A * (s^2 + (sqrt(A)/Q)*s + A)/(A*s^2 + (sqrt(A)/Q)*s + 1)

You can see that the linear gain A is also included as a root, sqrt(A).
If you look at it logarithmically, sqrt(A) is not the -3 dB point (that would be half the power or 0.7071 times the amplitude), but half the gain in dB.

 

[Matt Syson]

From my now patchy memory for shelving EQ curves the frequency was at the 3dB down (or up) from nominally flat.
For peaking bell for example they would be the frequency of the peak of the response bearing in mind low Q is quite wide.

 

[ruffrecords]

Looks like the 3dB point on the 180 curve happens at ~2k

That’s low Q!

Surely Q has no meaning in a shelving EQ.

Cheers

Ian

 

[MagnetoSound]

Of course, Ian is right. We call it slope, I think, as you would in a filter? But it still looks remarkably broad for a low shelf. I was pretty sure the Neve diagrams of old used to show the LF boost and cut beginning well below 1kHz. Were we being misled, or am I misremembering?

 

[abbey road d enfer]

Indeed there is no standard definition, but it's commonly admitted that the frequency indicated on the fascia is that where a "significant fraction" of the max amplitude is measured.
It is certainly not the +/- 3dB point, nor the 6dB, nor the "half-max".
Lots of variables here, since everyone has their own definition of a "significant fraction", and EQ's with +/-12dB Boost/Cut are different than those with +/-18dB.

 

[abbey road d enfer]

additional for those who want to know it in detail heres a mathematical derivation of a low shelf EQ

LowShelf: H(s) = A * (s^2 + (sqrt(A)/Q)*s + A)/(A*s^2 + (sqrt(A)/Q)*s + 1)

Care to elaborate? I would think that a shelving EQ, being based on two 1st-order filters, would not have a Q in its definition.
The Q you mention is the Q of what filter?

 

[abbey road d enfer]

Normally the Freuqency of an Shelving EQ is defined at half gain, in your frequency response for example the red one is 200 Hz.


View attachment 133664

Are you really sure the frequencies are marked as 120, 200, 400, 800 and 1600 Hz?
Wouldn't make much sense for many usrs; they would probably think it's a mid control.

 

[Gold]

The main problem in defining a shelf is that what makes sense technically for a high shelf doesn't make sense operationally. Unlike a low shelf where it does. For the red line I'd probably call that a 1K low shelf. Because it's boosting down from about 1K. This definition doesn't make operational sense for a high shelf. If you define a high shelf by the frequency at the top of the shelf, operationally it is the opposite concept of the low shelf. You are not boosting above the top frequency, you are boosting below the top frequency. For a high shelf it makes more sense to define it by the low end of the shelf, which isn't well defined technically. It makes more sense operationally though.

In other words you could define something that boosts or cuts between 1K and 10K either a 1K high shelf or a 10K low shelf. Some like Sontec call it a 10K high shelf, which is my least favorite way.