When you say "shelf" what do you mean?

Essentially, yes.

While that graph shows some shifting of the peaking frequency at different 'Q' settings, the important fact is that you refer to it by the peak frequency and not the 'break' frequency: inother words the frequency at which it deviates from flat.

A further hypothetical example: if you draw a typical set of fixed Baxendall curves, you'll usually find that the HF boost deviates from flat at right around 1kHz, perhaps achieving full boost at 10kHz and staying more or less fully boosted above that. -We call that a 10kHz shelf. -Likewise a 100Hz low boost would probably be fully boosted at all frequencies below 100Hz, then above 100Hz it descends gently to flat, settling down also right around 1kHz.

If we were to use the 'break points' in this Baxendall example, they'd noth be called 1kHz shelving rewponses... but the perceived frequencies at which they have effect are in actuality 100Hz and 10kHz... thus we call them 100Hz and 10kHz shelf responses.

Notice that the frequencies are fixed. A 1dB boost would have a slope of about 0.3dB/8ve, a 3dB boost would produce a resulting slope of about 1dB/8ve, a 10dB boost would produce a slope of about 3dB/8ve... so you cannot refer to the Baxendall circuit in terms of a defined slope response... it varies with boost (or cut of course!)

Looking at it the other way around, a theroetical perfect high-pass filter has a fixed slope, -6 or 12 or 18dB/8ve are typical examples- but you can't really vary the amount of cut, because it is fixed... It's fixed and defined by the precise distance (in octaves) away from the corner frequency. -There's no "cut amount" control.

Keith

Thanks all and especially Keith. I now understand. This is one of those things that I've never really understood. Since it's a basic audio tool I felt a little stupid for not understanding it. As with many things that seem like they are basic and easy there are subtleties that are hard to grasp. It took me close to five years to get a handle on pads. But I'n no electronics wiz. I hope some others filled in a hole in the foundation.

Accuracy is Our Policy Dept.: The great man's name was Peter Baxandall.

See Laurie Fincham's eulogy:

http://www.aes.org/aeshc/docs/jaes.obit/JAES_V44_9_PG796.pdf


EDIT:
I do think Fincham's speculation that Peter was the last great analog audio engineer is a bit limiting---I think there is still a squeeze or two left in the old design toothpaste tube. However, if you ever decide to argue something like that with Laurie, don't let it degenerate into a drinking contest. You will lose.

When I say "shelf" I mean somebody designed either cheap or odd EQ to compensate 6 dB / Oct artifacts of either cheap or poor designed gear.

[quote author="Wavebourn"]When I say "shelf" I mean somebody designed either cheap or odd EQ to compensate 6 dB / Oct artifacts of either cheap or poor designed gear.[/quote]
You really must get out more...

Keith

LOL! :green:

The easily entertained
gb

Just had a chance to start reading the fantastic SD console series and came across this well-put tidbit:

… A personal wrinkle, for which provision is made in the design, is to leave a small controlled amount of under-damped ‘bump’ in the filter frequency response. This has two consequences, one being slightly more rapid out-of-band roll-off but the other- a subjective effect-is that the extra programme energy introduced by the ‘hump’ serves to help offset the loss of energy in programme below the turnover frequency. The perceived effect upon introducing the filter is more of a ‘change in sound’ rather than a direct drop in lf response.
This raises an interesting possible line of debate: Should equipment in the recording chain (not just console) be designed and set up to be perfect according to conventional techniques and wisdom, or to sound ‘right’?
Steve Dove, Designing a Professional Mixing Console - Studio Sound May 1981

[quote author="Crusty2"]
…This raises an interesting possible line of debate: Should equipment in the recording chain (not just console) be designed and set up to be perfect according to conventional techniques and wisdom, or to sound ‘right’?[/quote]

To which I respond that either approach is fine, but I prefer the third option of allowing a useful amount of user control, where budget and pandel space permit.

Keith

[quote author="SSLtech"][quote author="Crusty2"]
…This raises an interesting possible line of debate: Should equipment in the recording chain (not just console) be designed and set up to be perfect according to conventional techniques and wisdom, or to sound ‘right’?[/quote]

To which I respond that either approach is fine, but I prefer the third option of allowing a useful amount of user control, where budget and pandel space permit.

Keith[/quote]

Steve designed enough consoles to know the right answer to that (rhetorical) question. That was a good series of articles, BTW.

Designing a console with a non-flat frequency response because it sounds good to you involves a subjective decision, that may not translate across a broad user base.

I don't mean to dismiss the well known and widely practiced perceptual frequency response relationships like balancing HF and LF skirts, and the specific use of under-damped LF poles in ported speaker designs to generate the perception of a better bass response. Electronic paths don't have the same practical limits at LF.

I advocate making the audio path flat and linear, but giving the customer as much control as practical to get where he may want to go.

Ironically when I was designing for a value/mass market, years later there was justification for reducing the control range in some cases to make it harder to get bad sounds. But recording and SR are different animals.

JR

The Maselec which is my main EQ is flat at the turnover. I often find myself boosting with a bell somewhere around there, but often I don't. All things considered I think for a mastering EQ this is best. I like to choose the parameters of the bump. I also have the luxury of spare bands to do this. On an SR console where time is short and options are limited I could see how a litttle bump there would be usefull.