Parametric vs Graphic EQ

[calpolyengineer]

What is the difference between Graphic and Parametric EQ? I already understand graphic eq but I can't figure out what parametric eq is. Also, are there instances where one is favorable to the other?

-Joe

[John Lyons]

Parametric Eq is usually 3 knobs. Cut/boost, frequency and Q/resonance. You can boost of cut a frequency make a narrow of wide frequency boost cut with the Q control and sweep through the frequencies in order to perfectly get the right sound. he Parametric EQ is used in the recording studio with surgical acuracy to fix problems. It can also be used to boost wide or narrow frequency regions. Basically an Eq in steroids! It can be subtle as well. A lot of EQ to play with as opposed to Graphic which is preset frequency sliders.

John

[calpolyengineer]

so basically an adjustable notch filter

[nosamiam]

so basically an adjustable notch filter

Yup, but it can boost or cut.  Do notch filters also boost?  Never used one so I don't know.  But I use Parametrics EQ's all the time.

And about the # of knobs... Sort of stating the obvious here, but... A fully parametric EQ has 3 knobs for EACH frequency it is affecting.  So an EQ with 3 knobs can only do one--albeit sweepable--frequency.  If you want one that can do a low freq, mid, and high, you'll need 9 knobs.

[Paul Perry (Frostwave)]

The thing wiht parametrics is, you can get much more 'extreme' results because, you can adjust the centre frequencies.
In a practical sense, I'd use parametric for stuff like percussion, and graphic eq for vocals or premixed sounds. But opinions will vary, widely!

[twabelljr]

http://www.geofex.com/Article_Folders/EQs/paramet.htm#variable_l

[Mark Hammer]

A "parameter" is just a characteristic of something, right?  If you adjust the "parameters" of something, then you adjust the characteristics independently.

An "equalizer" is somethat helps to adjust the frequency content so that it is balanced in some manner.

A "graphic equalizer" is simply one that uses slider pots so that points of emphasis (boost) and de-emphasis (cut) can be easily seen at a glance by the user (such as a soundman).

Typically, the more bands a graphic qualizer has, the more specific each band is, so that boosting and cutting at any particular frequency does not affect slightly higher and lower frequencies in a 31-band EQ as much as it does in a 5-band or 10-band.  The more bands, the more specific and focussed the effect of each pot is.

A parametric equalizer can often be the very same circuit as what is used in a graphic equalizer, except that where component values might normally be fixed in the EQ circuit to zero in on a particular range of frequencies, those values are made variable in the parametric EQ so that they can be adjusted.  Same circuit.  Just a question of whether you can tailor the parameters or not.

So, a 6-band graphic would try to cover a large part of the spectrum by having centre frequencies an octave apart (e.g., 125hz, 250hz, 500hz, 1khz, 2khz, 4khz). Because of their spacing, each EQ "section" would be designed to affect a broad range above and below its centre frequency.  Those very same sections, depending on how they are designed, could have changes made to them so that the specific centre frequency is adjustable, and so that they could be highly selective (just like a 31-band) or much less selective (just like a 5 or 7-band).  Same circuit, but by making some parts variable, those parameters can be adjusted.

[John Lyons]

Here is a Parametric Eq I built based on the Schematic at AMZ. The other single knob opposite is a LPB2.
I used a high band and a mid band. The mid band goes down to about 400 hertz.


Built from American Chestnut and Walnut on the bottom.

[Mark Hammer]

Very nice work.  Pretty.  Bet it gives a real woody tone.

It also illustrates something important about the difference between parametric and nonparametric EQ...

• If you don't know which frequencies you need to change, and you can't change how selective the boost/cut is, or where it needs to occur, you end up with lots of sliders.  They HAVE that many bands because the manufacturer has no  idea what you'll need to boost/cut and neither do you, so 31 bands leaves you..."prepared".  People who are accustomed to seeing racks of 31-band graphic EQs are a little uncomfortable when they see a parametric with a measly 3 or 4 bands of control. It just doesn't seem like enough to them.  However, because you can change where the boost/cut is applied and how broad/narrow and effect it will have, 3-4 bands of parametric can often provide as much control as 31 bands of fixed graphic EQ do.
• What you need for tailoring the acoustic response of a room, and what you need for shaping the tone of an instrument are different.  Rooms can have lots of different resonances, and if it is a matter of adjusting the room for a multi-source audio signal (drums, keyboards, vocals, guitar, bass, horns, etc.), you need to be able to provide a very detailed compensation at many different points in the spectrum.  If it is a matter of shaping your instrument's tone, 2 bands can be more than enough, when combined with switching pickups, instrument tone controls, amp controls, etc.  What basicaudio shows is close to as much EQ control as you'd want

Note as well that there also exists the category of "semi-parametric" EQ, which is basically halfway between graphic types and full parametric.  Here, there is no adjustment (at least on the control panel) for selectivity or Q of each resonant section, just boost/cut and variable centre frequency.  Somehing like what basicaudio has (i.e., 6 knobs), but with 2 bands of semi-parametric and a treble and bass shelving EQ, would provide gobs of control for most users.  Just pick a Q for parametric sections that strikes a good balance between  pickiness and wide effect.  In fact, it would not be unreasonable to picky a narrower boost/cut for the lower range, and a wider one for the upper range, or even have two overlapping sections (e.g., one you could tune from 200hz to 1khz and another you could tuine from 400hz to 2khz) with one set for high Q and the other set for lower Q).  Happily, the articles at GEOFEX provide plenty of how-to information.

[rockgardenlove]

Where's the shematic for that parametric EQ basicaudio made?  I didn't see it anywhere online.

[RDV]

Where's the shematic for that parametric EQ basicaudio made?  I didn't see it anywhere online.

http://www.muzique.com/amz-cd.htm

RDV

[toneman]

RDV, 

did U mean *this* article???

http://www.geofex.com/Article_Folders/EQs/paramet.htm

[John Lyons]

Yes, sorry. I built mine from the information from GEO not AMZ. Silly me!
John

And yes mark, I wood (pun)  agree with you.

John

[343 Salty Beans]

I learned this in calculus today.

"Parametric" means "simultaneous". And that was the only part I heard cuz it had to do with music.

[Paul Perry (Frostwave)]

That's tragic, Saltybeans! the only thing you learned in calculus today was wrong!  (maybe there was something to do with parametric equations..)

[calpolyengineer]

Parametric equations are where two variables are both "modulated" so-to-speak by a third variable (usually time)
So x=f(t) and y=g(t) so to graph x vs y you would solve for the points (f(t), g(t)) for all t in your interval.

They are simultaneous though because the functions f and g can be really crazy equations, but they are both simultaneous with respect to t.

[Ge_Whiz]

Hmmm, thanks for the graphic explanation. Yuk yuk yuk.

[343 Salty Beans]

You and your cal poly-ness.

Cal Poly Pomona? I'm like ten minutes away from there.

On a random tangent, isn't g usually the inverse of f?

[Paul Perry (Frostwave)]

Thanks calpolyengineer! I can see me havign a few questions for you!

[George Giblet]

For parametric equalizer parameteric just means the parameters for the bandpass/finite notch boost/cut filter is adjustable.  The adjustable parameters are boost/cut, the frequency and the bandwidth of the equalizer - for a second order equalizer there are no more parameters to play with.  Instead of defining the bandwidth of the filter you can also parametize the filter with the Q of the filter as the adjustable variable.

On a graphic equalizer only the boost/but parameter is adjustable and there is generally more than one band.  .  For each band the frequency and bandwidth is *conceptually* fixed.  Also The term graphic comes from the fact the boost/cut controls represent a graphic picture of the frequency response.

In reality:

- The bandwidth is not constant.  More often than not the bandwidth is a function of the amount of boost/cut - and yes that applies to parametric equalizers in spite of the band or Q setting on the panel.  See the Rane corporation documents on "constant Q" equalizes to get a handle on the issues.

- For graphic equalizers the panel rarely represents the frequency response.  The bands interact.  The true amount of boost/cut, bandwidth and centre frequency for a given band depends on where the other bands are set - again in spite of the appearance of the control settings.  Different equalizer topologies interract in different ways.  Rane corporation have some documents on this too.

As far as the mathematics goes the parameter can be arbitrary (doesn't have to form inverses or anything).

For example a circle is defined as x^2 + y^2 = r^2 (a relation).  If x is made the independent variable and y the dependent variable the circle cannot be represented as a function since there are two y values for each x value.  You need to a separate function for each half ie.
y = sqrt(r^2 - x^2) and y = -sqrt(r^2 - x^2).  In parametric form you don't have this problem,
x = r cos(theta), y = r sin(theta) where the parameter theta goes from 0 to 2pi.  Now the parameter is arbitrary  I could easily have written
x = r cos(2 pi t), y = r sin(2 pi t) where the parameter t goes from 0 to 1.