Another forum post ..... lengthy but hopefully useful for some of you out there .....
---------------------------
Regarding guitar frequencies, the first thing I had to do was find out just what a guitar's frequency capabilities are. For standard tuning (some of these are rounded off for approximations):
Lowest note on a guitar
Open low E string = 82 Hz (approx)
(E octave 3)
(For comparison, the lowest string on 4 string bass = 41 Hz)
Highest note on a 22 fret guitar:
(D octave 7) note = 1175 Hz
let's take it up a whole step for 24 fret guitar or high bends:
(E octave 7) note = 1319 Hz
So you quickly see anything we hear on a guitar above 1200-1300 Hz or so are harmonics. I haven't found much benefit in cutting or boosting anything above 5k. To be honest, I haven't spent much time on anything up as high as 7-10k, as the amount of difference in tone is not significant with the amps/speakers I'm using.
There's also not much available in a guitar speakers' high frequency response. There's not much available above 10k or so, and it's dropping off pretty fast at about 7k. Take a look at a freqency response curve for a Celestion Blue:
So any EQ'ing you do above 7k would seem negligible.
One thing the parametric seems to do though is help you find the sweet spots, letting you fatten them up. You can also notch out some frequencies to get interesting tones you might not ordinarily hear from a guitar.
One last thing I think a parametric might do for you is in a live band or recording situation where you'd want to avoid conflict with vocals (and allow you to keep stage/house volumes lower). Here's a good page with frequency references for band and vocals and what you can be done from the front of house perspective. I'd say you might find modifying the guitar itself to avoid conflict with the frequencies other instruments occupy. Here's some related EQ information (written from the perspective of a mixer) that talks about what frequencies different band instruments occupy (I'm copying into this post because I found it very hard to read on the web page):
http://www.bluesblast.com/frequency.txt
Using the Equalizer Effectively
One of the biggest mistakes to make when using an equalizer is to boost or cut frequencies above or below the dominant energy of the instrument. As mentioned earlier, these ranges extend far past the fundamental frequency of the instrument.
The following paragraphs outline specific equalization applications for various instruments as well as some settings that should be avoided.
Vocals
Low frequency boosts are almost never effective for female vocals, but may be effective on male vocals to a limited extent. Boosting of lower frequencies from 500 Hz to 800 Hz will add body and warmth to the vocal. The most distinct vocal clarity range is from about 3.5 to 6 kHz. This range will enhance breath effects as well as increase the overall intelligibility of singing and speech. This boost does not come without penalty. Excessive boost in this range increases the sibilant [pronounced sib·i·lant (sîb¹e-lent)] effect of the voice. Sibilance occurs when the vocalist pronounces words with the letter "s". If a vocalist naturally has this problem, cutting the 3.5 kHz to 6 kHz range can cure the problem. Beware that this is the presence range of intelligible speech and too much cut will make the vocal sound muddy. Also presence may be added in the 1 kHz to 3 kHz range although, the 3.5 kHz to 6 kHz range is generally suited better for overall clarity.
The other problem with boosts in this range is vocal microphone feedback. Directional cardioid dynamic microphones are almost always used for live vocal performances. The cardioid pickup pattern created by the design of the microphone is quite effective. The overall pattern of the mic and monitor or main speaker tend to be less directional and predictable at the 3.5 kHz to 6 kHz region. It is unfortunate that this vocal clarity range must have the inherent pitfalls of transducer physics. Feedback will inherently occur freely at this range.
Bass "Kick" Drum
It is hardly ever effective to boost frequencies of a kick drum below about 60 Hz. There are applications on some modern dance music where synthesized drum patches will have dominant energy below 50 Hz. These 20 to 40 Hz fundamentals are the type that easily propagates through the closed windows of automobiles and other structures. These low frequency waves encounter little acoustical attenuation in materials and may be heard from great distances. For the generalized kick drum application, the "thump" is usually realized in the 60 Hz to 100 Hz range. The definition or "slap" of the kick drum is very essential for its relationship to the bass guitar. Boosting the kick drum at 60 to 100 Hz for the "thump" and boosting 1.5 kHz to 3 kHz for the "slap" will provide a "spectral saddle" for the bass guitar to reside. Boosting bass drum frequencies from 100 Hz to 2 kHz in excess will often cause the kick drum and bass guitar relationship to be very boomy and muddy. Letting the kick drum initial attack in the 1.5 kHz to 3 kHz region start off the event, and letting the bass guitar fresh string harmonics provide the sustaining clarity, provide a pleasing spectral combination.
Snare Drum
Older audio references will refer to snare drum dominant frequencies being in the 1 kHz to 2 kHz region. If you are mixing sound for modern rock or country music you will find a potpourri of snare drum frequencies. Starting with disco in the 70's and the urban cowboy country craze of the early 80's, snare drum became spectrally similar with a bass drum. Experiment with a multi-octave equalizer on a stereo system with an early to mid 1980's country record, like George Strait. You will find very dominant snare drum spectral content in the 150 to 200 Hz region. Mixes of that era as well as today use caution in not having the snare and the kick drum both being dominant in the mix since it would be difficult to tell the difference between the two drums. This often results in a "double time" effect. There are no general rules to the equalization of the snare drum with one exception. When using a real snare with a microphone, be aware that if the drum is tuned very high like a marching band snare, excessive low frequency boosts will not create a fat snare. Listen to the real drum sound up close and realize that fundamental frequencies that are not available from the drum cannot be created or synthesized by equalization. Excessive boost at low frequencies will cause pickup of other drums undesirably.
Generally, if a trigger snare patch or drum has energy in the 150 Hz range and you desire a fat snare, then use it accordingly. Some crisp quality can be added in the 2 kHz to 5 kHz region. Remember however that excessive boosting of any frequency of a snare drum means you are probably trying to get a sound that is not available from the source and you are likely picking up extraneous sounds from other nearby sources. Snare drum reverb is a diverse topic alone. The reverb usage will greatly affect overall equalization used.
Toms
Depending on the tuning of the toms, most of the effective range is from 150 Hz to 2 kHz. The lows are good for deep percussive effects but definition that cuts through the mix is usually about 1 kHz to 3 kHz. One advantage of toms particularly in a country or contemporary mix is that they are only played occasionally. That means their level and occupancy of spectral space may be loud and wide. They don't need to repetitively compete with other instruments like kick drum and bass guitar. The application of reverb also effects equalization as mentioned in the snare drum topic.
Cymbals
Fortunately, cymbals remain fairly constant and predictable over many types of music. Their dominant energy lies in the 2 kHz to 5 kHz region. Cymbal harmonics extend up to and past the range of human hearing. Boosting of cymbals in the 10 kHz to 12 kHz region results in a very brittle sound. Usually, boosts in the dominant area of 2 kHz to 3 kHz makes the overall mix less "wet" or "noisy" than boosting in the upper region.
Electric Bass
As with the discussion of drums, boosting lower frequencies to try to create more depth than what is available is a common mistake. Most bass guitar energy lies around 100 Hz with definition in the 1 kHz to 2 kHz region. Boosting of very low frequencies will result in a "muddy" clash with the kick drum. Letting the kick drum make the fundamental, and the bass guitar rounding out the low midrange just above the kick drum results in a more clear discernible mix. The kick drum can have high definition attack for the initial hit while the bass guitar string harmonics can provide the sustaining definition for the sound.
Electric Lead or Steel Guitar
The most important rule for equalizing guitars is to realize that harmonic series content not available at the source cannot be generated or synthesized at the mixer. Most guitar and steel guitar energy lie between 80 Hz and 5 kHz. Boosting the 3 to 5 kHz range will add clarity to clean guitars but will sometimes add harsh harmonics to a distorted guitar.
Acoustic Guitar
The same frequency range applies to the acoustic guitar as the lead electric guitar. One common mistake is to listen to the acoustic guitar too much by itself rather that with the entire band. One common mistake with the solo acoustic guitar is to add too much bass. A solo acoustic guitar seems to need more low frequency boost to round out the sound than it does when played with a set of other instruments. If the low frequencies are excessively boosted, this results in a very muddy relationship with the overall mix. Remember that the acoustic rhythm guitar is as much a percussive timing component as a melodic component. Its high frequency spectrum is most essential to the "sizzle" of the program material.
Overall Equalization
Excessive boosts of cuts in the main system EQ will drastically effect the decisions made at the individual channel EQ. One method of enhancing vocal clarity is to make sure that all other instrument individual mixer channel equalizations do not occupy the 3.5 kHz to 4 kHz band so much. The perception of presence of vocals and instruments can also be simulated by restricting other instruments to have dominant energy in that band. One common mistake for a sound engineer to make by listening to each instrument individually is to make each instrument sound very clear and present. It is easy to boost all instruments in this 3 kHz to 4 kHz range. The separation of sounds is more often achieved by spacing their dominant energy in bands not significantly occupied by others.
The most obvious mistake is excessive amounts of equalization. Experimentation with an equalizer in a home stereo system is a valuable tool to recognition of the various frequency bands. In summary, live or recorded mixing is very objectionable, and remember not everyone will have the same opinion.
