Minesh Patel

Difference between Parametric & Graphic EQ

There's a lot of talk & interest in the new receivers from Pioneer Elite & Yamaha that do auto-equalizing of the room. But I don't know what's the difference between the two in the type of equalization they use, e.g. graphical vs. parametric.

BruceD

This is not completely accurate, but may give you some idea about EQ operation.

If you think about a roller-coaster track, and how steep or gentle the "rise to the top and drop to the bottom" is, that can be like a representation of an EQ filter's operational bandwidth (how many frequencies if actually corrects or affects).


For graphic EQs it is mostly a gentle slope over a full octave (not user adjustable). The center frequency (top of the track) is also fixed and usually can't be adjusted by the user (they call this 7-band, 10-band or 1/3 octave). This changes a lot more frequencies in addition to the specific frequency you are trying to correct and is similiar to a "tone control" and thus less desirable.

For Parametric EQs, a filter's steepness(sp?) or "Q" is typically controlled by the user and can be as narrow as 1/60th of an octave or as wide as one or more octaves. This means you can be selective and only correct the problem frequencies, leaving adjacent frequencies untouched. The center frequency is also user controlled.

An octave is a doubling of frequency, for example, it's one octave from 40Hz to 80Hz and it's one octave from 500Hz to 1000Hz.

PaulT

Graphic Equalizers have fixed frequencies in which you can adjust the gain at that frequency only.

Parametric Equalizers have adjustable centre frequencies, bandwidth adjustment (how far on either side of the centre is affected) and gain control.

You may have seen Graphic Eq's alone or in equipment as a row of vertical sliders.

Ahhh, I see you beat me to it BruceD

Parametric would be the better way to go due to a much better adjustment range.

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Bill Polley

a graphic EQ is what most people think of as an EQ. It has a number of sliders equally spaced across the frequency spectrum, anywhere from 1/6 octave apart to a full octave apart. Each slider acts as a tone control, basically a better defined bass and treble control (like having 10 knobs). When set, the EQ sliders give a graphical presentation of their settings, hence the name.

A parametric EQ is a much more flexible beast. It allows a person to set the exact frequency to affect, the bandwidth (how much to adjust on each side of the set frequency), and the amount of gain or cut at the particular frequency.

If you have a large hump in response at 50hz, and have a 1/3 octave graphic EQ, you would need to adjust at both 40hz and 63hz, and would affect frequencies as low as 20hz and as high as 125hz with most consumer models. With a parametric, you can set the frequency to be cut to 50hz, set the bandwidth to affect only the frequencies that are part of the hump, and adjust the gain until the response is smooth throughout the region.

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Minesh Patel

Thanks for the replies. I guess parametric really is the way to go. I'll also guess that stand-alone parametric eq's are relatively expensive, and will also require test equipment to use properly. Pretty cool of Yamaha to use that in their latest receivers.

Marty Neudel

I'm going to fly in the face of conventional wisdom by pointing out that, in many cases, a well-designed graphic equalizer is the better choice.

If you have the equipment that enables you to measure the pesponse characteristics in many points of your room, and if you know how to use the formularly used to set the parameters of the p.e., then the p.e. will give you considerably better performance.

If you don't have the equipment or do not have working knowledge of the formularly, then a g.e. is likely to do a better job for you.

The above applies to expensive ultra-high end consumer and professional grade equipment. At the level most of us purchase, we are really dependant on the manufacturer to choose and implement the most effnoective solution for our price-point.

Note the following two points: 1)In a good g.e., the curve is designed to compliment the bandwidth, making it considerably easier fot the user to obtain the equalization he needs; 2)In many p.e.'s there aren't enough equalization steps to satisfy the needs of the particular room.

The best advice is to audition the unit you want at home. If your processor (or receiver) gives you the quality of performance you require, then it is the right unit for you.

Marty

BruceD

The frequencies that need EQ in almost all Home Theaters are the bass frequencies (typically <80Hz).

Unfortunately, graphic EQs are simply ineffective at correcting bass mode peaks, which are called room modes because they are bass frequency reflections that are a direct result of the room's dimensions.

My problem with Yamaha's YPAO implementation is that they hard code the center frequencies (typically 1/3 octave spacing). They also skimp on the bass frequencies, only hard coding the center frequencies of 80Hz and 63Hz in the bass frequency region (simply inadequate and not low enough in the bass frequency region in my opinion). But, Yamaha is the only one offering parametric EQ in the digital domain, so at least it's a good start.

The BFD 1124 (from Behringer) is a parametric EQ with 12 parametric filters per stereo channel (24 filters total for frequencies as low as 20Hz), that can be used on the sub-out channel to correct room mode problems. This unit is typically available for about $100 (very inexpensive). If you search this forum you will see hundreds of threads on BFD and hundreds of HT enthusiasts as users, it is that popular.