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→Pre vs. Post EQ
== Pre vs. Post EQ ==
The way filters impact the audible tone of the guitar signal depend on their location in the signal chain, particularly in relation to distortion stages. Because most signal chains only feature one (or at least one ''main'') distortion stage, EQ is often refered to as ''pre-EQ'' if it processes the signal before that distortion stage or ''post-EQ'' if after.
Distortion typically works by boosting a signal level past a threshold that the circuitry or algorithm can reliably process. The part of the signal that exceeds the threshold is clipped off. This reduces overall dynamics, serving to compress the signal. Frequencies that were barely audible before distortion may be boosted near the threshold, becoming just as audible as those that were attempted to be boosted past the threshold. By clipping the signal, distortion makes the waveform more similar to a square wave, adding lots of high-order harmonics above the clipped frequencies.
=== Pre-EQ ===
Pre-EQ can alter which frequencies get pushed into distortion vs. which ones are simply boosted up towards the threshold and thus become more audible. I classify distortion into one of three types:
{|
! Distortion Type !! Characteristic Sound !! Created by Pre-EQ
|-
| Fuzz || Loose, flubby low-end and raucous, buzzy tone; intervals and chords sound like each note is fighting for prominence || Prominent bass and either scooped or flat mids
|-
| Crunch || Crisp rhythms and creamy leads; neither loose nor tight || Flat or prominent mids, low to medium bass
|-
| Metal/Lead || Very tight, thick bass response and searing high-end with lots of high-frequency harmonics || Prominent upper midrange and treble with low bass
|}
These roughly correspond to dark, neutral, and bright tones. Of course, the distortion stage used also has a large impact on what kind of tone you will get. Don't expect to get a metal tone from a fuzz stompbox simply by pre-EQ'ing.
Here's a guide what to expect tonally based on whether the tone is pre-EQ'ed to make certain frequencies prominent or deficient:
{|
! Freq. Range !! Prominent !! Deficient
|-
| 0 - 150 || Muddy || Thin
|-
| 150 - 250 || Fuzzy || Thin
|-
| 250 - 500 || Creamy || Cold
|-
| 500 - 800 || Flat || Tinny
|-
| 800 - 1,500 || Djenty || Buzzy
|-
| 1,500 - 3,000 || Crispy || Sterile
|-
| 3,000 - 7,000 || Searing || Honky
|-
| 7,000+ || Gritty || Smooth
|}
== Common EQ Techniques ==