How do you use a parametric eq (like a Boss PQ-4)?

KissTone

Silver Supporting Member
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3,128
I was just reading a posting on another site by a guy who uses a Boss PQ-4 to tweak his tone, but I really have no idea what a parametric EQ does and/or why one would use one. Can someone enlighten me? Thanks.
 

John Phillips

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13,038
It's like the four EQ bands (bass, middle, treble, presence) that you get on amps, but instead of having one knob for each, you can control the frequency as well as the amount of each so you can more finely tune them. In fact, only the two middle (equivalent to mid and treble) bands are tuneable on the PQ-4, so it's a bit more limited, but also simpler to set up. (A true parametric EQ has all the bands fully adjustable, and also has 'Q' or band width controls for each too.)

The difference in mid frequencies can be important, it's a big part of the difference between a Marshall and a Mesa tone for example. So it would let you set up fairly different tones if you use the amp for your 'normal' one and then impose a different EQ on it for your 'alternate' one.
 

pgissi

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2,478
...if not used properly

Parametric EQ does more than adjust the amplitude of individual Freq Bands like a Graphic EQ, it alters a range of adjacent freq bands determined by the Q setting of its filter and is typically adjustable in larger units. The Q is the bandwidth of the filter or the range of afffected freq's.

If the Q is not adjustable the it can be said to be Quasi or Semi Parametric

Parametrics can also employ some additional Shelving EQ like Bell Shaped, Bandpass, Low Pass or High Pass types but this is limited to more complex rack units for pro audio processing.

To relate Parametric in a practical sense-

For example, say you want to alter the region between 300 and 500hz in a signal. Using a graphic to accomplish this is easy and in this example a simplistic assumption is that for some reason, graphic is not adequate here.

The solution would be to use a Parametric EQ with its center Freq somewhere close to mid-point between the desired affected range of 300 to 500hz. If the Q is adjustable you could accomplish this with 1 filter to include the desired range and this is adjusting the bandwidth of the filter.

Once you have the Q set, adjusting the filter alters the balance of freq's controlled/affected by the filter. The Q can also be set Narrow, lower bandwidth to where a smaller range or even 1 freq (precision types) can be affected.

Parametrics are often called the most powerful eq types and typically employ + or - 15 to 20db boost/cut. Where a graphic EQ can be used to adjust freq response for a room, parametric can be used for Tonal emphasis or de-emphasis (tonal correction) of a source to rid it of noise or boost its fundamental freq to increase its apparent loudness in a mix without over boosting it.

Parametrics are the most difficult to use of all EQ types and when improperly used can be worse than no treatment.

The most useful guitar application of parametric EQ for me is to dial in a more acoustic sound from an electric guitar, suck out the mids to clean up an electric for psuedo acoustic tone. I tend to avoid using it for my guitar tone in general and that is more representative of whats available and practical, having good tone than its usefullness.

Wider bandwidths (Q setting) sound more natural generally but if improperly used, you could end up in nasal tone city or be boosting too much of what you dont want and masking what you want.

Proceed cautiously
 

KissTone

Silver Supporting Member
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3,128
...if not used properly

Proceed cautiously

Ah, jeez. Now I'm scared.;)

Thanks for the info. My limited knowledge of parametric EQ relates to my only exposure to it: a friend had a SS Yamaha amp back in the 80s with a 'parametric' mid control as I recall. I just remember that one knob selected the mid frequency and another knob was then the boost/cut of that mid frequency.

So a graphic EQ has frequencies preset, say for example, I can cut or boost at 1k----but a parametric would let me cut or boost the frequency of my choosing?
 

pgissi

Member
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2,478
Just be aware that it can not be as pleasing as your expectations

So a graphic EQ has frequencies preset, say for example, I can cut or boost at 1k----but a parametric would let me cut or boost the frequency of my choosing?

Yes, the freq centers are preset on a graphic and adjustbale on a parametric and I am guessing the boss may allow for adjustment of especially 1k, the telephone sound freq which is the enemy of metalheads everywhere.

If you want to sound like that fraud Alexander Graham Bell, the annointed inventor of the telephone, calling his minion Watson in some tinny voice, boost 1k as much as you can.

I expectthe boss is designed to compliment guitar tone so it may actually be more pleasing than try to use a full blown parametric

Since the guitar range is what 160 to 6k (low E is 160 in standard tuning) and is not considered a full range 20 to 20hz signal, using parametric sparingly will get the most mileage

But then again, you may be on the verge of some groundbreaking thing so dont be worried to toss the rules if thats what gets you there.

As I always say, the real test is on a loud stage with a loud and obnoxious rock band, if its right, it cuts like a knife, slaying all those who defy

Sorry, 70's/80's prog metal reference creeping in
 

g-nem

Member
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1,070
I've always dug parametrics because they are so flexible. They are good 'problem-solvers' - say you have a guitar with a weird mid-range hump, or bass resonance, etc- these are easy things to dial in or out with a parametric. The key is to slowly sweep the frequency knob to hear which frequency you are affecting.

There is no reason to be afraid of a parametric EQ- you just have to listen to what you are doing, and be subtle. Just like on a graphic EQ you wouldn't boost every knob to +12, on a paramtric small boosts at the right frequencies can make a big difference. I wish there was a super small parametric EQ pedal readily available- they are hard to find, and ones made for guitar tend to not be transparent or widely adjustable.
 

GeeerJunkie

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5
I would like to simplify the description of what the Boss PQ-4 pedal is and does, and how to use it.

Think of this as an EQ Pedal with 4 EQ Bands you can control, essentially Bass, Lower Mid-range, Upper Mid-range, and Treble. Additionally, you can decide the center frequencies of the two "midrange" controls, and you can control the overall gain or cut in volume of the pedal. You cannot control the specific Bass and Treble frequencies.

I simplified that description as some of that "lower mid-range" could rightfully be called upper bass frequencies, and some of what I'm calling "upper mid-range" can rightfully be called lower treble frequencies. But that's what happens when you simplify.

The reason this can be powerful for a guitar is because most of what you want to hear cutting through the mix is happening with the two middle controls (lower and upper midrange, i.e between 100 to 8000 Hz, and especially between about 1000 and 4000 Hz.

From left to right the knobs are controlling:

The LOW knob controls the boost or cut in ALL FREQUENCIES BELOW 100 HZ. This is what I'm calling the "Bass" control.
The PRESENCE knob controls the boost or cut in ALL FREQUENCIES ABOVE 8000 Hz. This is what I'm calling the "Treble".
The MIDDLE knobs control the specific frequency and the level of boost or cut, of a band of frequencies centered on any frequency you choose from 100 to 1600 Hz. This is "Lower Mid-range".
The HIGH knobs control the specific frequency and the level of boost or cut, of a band of frequencies centered on any frequency you choose from 500 Hz to 8000Hz. This is "Upper Mid-range"
The LEVEL knob controls the overall gain or volume of the pedal output.

When I say a "band of frequencies" I mean a bell shaped curve (or upside down bell if cutting). So if you center the band at 2000 Hz, you are also adjusting frequencies to the both sides of that center point, but the amount decreases the further you get from that center point.

A truly parametric EQ lets you adjust the width of that bell shaped curve as well. The Boss PQ-4 does not allow you to do that however.

You can use it to shape your tone, or you can use it to eliminate weird feedback frequencies using the "cut", but a notch filter is better for that.
 
Messages
12,568
A parametric lets you choose the most important frequency and do whatever you want with it. If you have multiple bands you can alter that many frequencies.

It gives you complete control, way beyond a graphic or other tone controls.

It does take a learning curve and good ear to work properly. But once you get used to it like I have, it is the only way to go. To me parametrics are easy, but I have been using them forever.

Whatever your imagination can think is what you can have with a parametric.

If you don't know what you are doing and just start turning knobs, well, then you are likely to be very disappointed with a parametric. But don't be scared. It just takes a little while of messing with them, then you are set for life.
 

DaveKS

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we-have-to-go-back-to-the-past-we-have-to-go-back.jpg



Nice thread resurrection.
 




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