EQ

EQ-ing tools

• The Axe-Fx II offers a large number of EQ tools:
  • Parametric EQ block (PEQ)
  • Graphic EQ block (GEQ)
  • Global EQs
  • GEQ in the Amp block
  • Low and High Cut in the Cab block
  • etc.

Contribution from forum user Clarky

Graphic EQ [GEQ] and Parametric EQ [PEQ] are very different animals. This is not specific to the Axe as most reasonable quality fx-units will contain blocks that offer EQ with the same / similar functionality.

Graphic EQ - this has multiple frequency bands where the central frequency of each is fixed. Example: If your guitar amp has 4 tone controls - bass, mid, treble, presence - you can think of this as being a 4 band GEQ. Each 'band' [tone control] effects a pretty wide range of frequencies. The 'width' [the frequencies it effects from lowest to highest] of the band is called the Q. In a GEQ you can't change this, you can simply adjust the level of each band by boosting or cutting - using +ve or -ve gain values respectively. An 8 band GEQ is more of the same but by having more bands you have more detailed control and each band's Q is therefore narrower. Try thinking of an 8 band GEQ as having something like - low bass, mid bass, high bass, low mid, mid, high mid, treble, presence. Likewise a 16 band GEQ would have even more controls with narrower Q values that sit in between the bands described above. This being the case a GEQ is pretty straight forward to use. You simply boost / cut the various frequency bands to taste.

Parametric EQ - far more flexible but there are a few things you need to understand to get the best out of it. Each band has a Q control. This means that you can change the width of the band - and therefore the spread of frequencies that a given band effects. Low Q values create a wide EQ range and high values create very narrow range. This means that you can have very general EQ control with values from 1.0 or lower [not unlike a bass control on an amp], or have precise control [usually corrective] with narrow values such as 1.8 and above. The 'frequency' control in a PEQ allows you to change 'where' in the frequency spectrum the PEQ band is centred [and therefore the frequencies that it acts upon]. So unlike a GEQ with it's fixed bands, a PEQ band can effectively be moved up and down the frequency spectrum and made wide or narrow. In addition, the first and last PEQ bands can also have their filter type altered. Whereas the inner bands use a 'bell shaped curve' to effect the frequency band, the outer bands can be set to bell curves, hi-pass filters [let hi freq pass], low-pass filter [let low freqs pass] and more. This allows yet more EQ refinement.

Frequencies important for guitar:

Note: a guitar is actually a tenor instrument [despite all our music being written with a treble clef] so in general terms we can get pretty low [concert tuned]. Our low E is just a little higher than the low C of a cello [which is a bass instrument]. The numbers below are just a rough guide.

Sub bass: this is below 80Hz - guitars actually produce sounds lower than their lowest notes via sub-harmonics etc. This area of the frequency specrum generates a sense of power and energy in a mix. It's the 'shock and awe' area of the mix. However too much can cause a loss of clarity. Many produces will cut everything below 50Hz to tighten the tone.

Bass: 100Hz to 400Hz - this is where all the power is in guitar terms. Too much will destroy your definition and make you sound woolly.

Low mids: 400Hz to 800Hz - this is where your thump is. Low mids and bass beth generate a lot of energy [electrically and in terms of moving air] and at times can get in each other's way. If you want deep bass then scoop these out a little. But beware, a lack of low-mids will get you lost in the mix. The relationship between bass and low mids is critical. Tip - Never lose sight of the fact that your bassist provides most of the the deep bass. So often you can get away with using less bass and more low-mid in the mix. and between the two of you there will be plenty of low stuff in the mix. It's not unusual for tones that sound killer in isolation to not sit well in a mix, and in contrast, tones that sound a little lacking in the low stuff to sound great in the mix. It's all about the different instruments leaving space for each other and inter-acting with each other.

Mids: centred around 1KHz - this is what cuts you through the mix. Too much and you'll sound nasal, not enough and you'll vanish in the mix.

High mids: centred around 2.5KHz to 3KHz - this is where you get your definition. Too much and you sound shrill, not enough and the leading edges of your notes will vanish. And it's for this reason that legato centric players [in the Satriani mould] tend to like to roll off this band a little to 'warm up' and 'soften' the tone. Whereas full-on riffers, alt-picking shredders and percussive players [like funk] like this band to be a little stronger to add attack and definition.

Treble: centred around the 5KHz area - this adds all the sparkling highs. Too much becomes piercing and brittle sounding. Too little make your tone sound confined and lifeless. For those of you that create presets in stereo, it's the upper frequency ranges [high-mids, treble and presence] that convey the sense of 'spread'. The general rule is that the higher the frequency, the narrower the beam [from the speaker cone] is and therefore the more directional it becomes.

Presence ['air']: is from 7KHz or 8KHz and up - guitars don't do a great deal up there. Some effects though will generate harmonics up there [especially distortion centric effects]. In the studio you'd tend to use this on the mix overall or on cymbals / synths etc. Depending on the fx you have running in the chain it is worth experimenting with this band to see if it adds or fixes something, but don't be too surprised if you do not perceive a great deal happening. I tend to think that the general tonal impact is not be as strong as with the treble bands."

7 Bad System Dwarves (Axe-Fx II manual)