EQ types: graphic, shelving, Pultec, dynamic, linear phase, M/S

Overview

The parametric EQ (see the “Equalizer (EQ)” guide) is the basic tool. The other types exist because they solve specific problems: speed (graphic), color (shelving, Pultec), problems that come and go (dynamic), phase (linear), stereo image (M/S). Knowing which type to use is worth more than knowing dozens of plugins.

Graphic EQ

• What it is: fixed-frequency bands with fixed Q, one per slider. ISO standard: 10 bands at 1 octave (31, 63, 125, 250, 500 Hz, 1, 2, 4, 8, 16 kHz) or 31 bands at 1/3 octave (from 20 Hz to 20 kHz).
• How it works: each slider is a constant-Q bell; moving several adjacent sliders produces a curve. The bands overlap, so a slider also affects its neighbors.
• When: live, quick correction of the room or monitors (today dedicated systems are used), broad-stroke color on synths and guitars (graphic pedals). In modern mixing it is used little.
• In FL Studio: Fruity 7 Band EQ (simple graphic), EQUO (EQ with drawable sliders).
• Mistakes: a “smile” (bass and treble up, mids down) on everything: the mix loses presence and vocal.

Shelving

• What it is: raises or lowers all frequencies above (high shelf) or below (low shelf) a corner point. The indicated frequency is usually the half-gain point.
• Parameters: corner frequency, gain, shelf slope or Q. With high Q many EQs create a “resonant” shelf (a small dip before and a bump after the corner point, Neve/Pultec style), with low Q a smooth transition.
• Typical values: air high shelf 10–12 kHz +1/+3 dB; low shelf 80–120 Hz +1/+2 dB for weight; low shelf 200–300 Hz −2 dB to “warm by subtracting” on pads and guitars; high shelf 6–8 kHz −2 dB to darken an aggressive cymbal.
• Baxandall: very wide, soft shelves (hi-fi tone-control type), excellent in mastering: +1 dB at 20 kHz centered around 10 kHz opens up the sound without harshness.
• Tilt EQ: a single control rotates the spectrum around a pivot point (e.g. 800 Hz–1 kHz): +1 dB tilt = treble up and bass down. Excellent for buses and master.

Passive Pultec (EQP-1A and similar)

• What it is: a passive tube EQ from the 1950s; the passive network loses signal and a tube gain stage recovers it, adding color.
• Low section: selectable frequencies 20, 30, 60, 100 Hz; separate Boost and Atten knobs (shelf). The famous Pultec trick: boost and atten together on the same frequency. The two curves don't coincide (the attenuation acts a little higher), so you get a bump in the sub and a dip above it (about 150–300 Hz with 60 or 100 Hz selected): full bass but not muddy. The original manual advised against it; in practice it has become a standard.
• High section: bell boost with frequencies from 3 to 16 kHz (3, 4, 5, 8, 10, 12, 16 kHz in most EQP-1A emulations) and a Bandwidth control (sharp–broad) for the Q; separate shelf attenuation at 5, 10, 20 kHz.
• Starting values: kick 60 Hz Boost 3–4, Atten 2–3; bass 100 Hz Boost 2–3, Atten 2; vocal High boost 10–12 kHz at 2–4 with wide bandwidth, Atten 20 kHz at 1–2 if it gets harsh; master/bus 30 Hz Boost 1–2 and High 16 kHz Boost 1–2. (The scales run from 0 to 10 and are not in dB.)
• Other passive/color EQs: MEQ-5 (mids), Neve 1073 (shelves and mids at fixed frequencies), API 550 (proportional Q), Maag EQ4 (Air Band 2.5–40 kHz), Manley Massive Passive.
• Plugins: UAD Pultec, Waves PuigTec, IK Multimedia, Softube and several free Pultec-style clones. FL Studio has no stock Pultec: approximate it with a low shelf + bell in Fruity Parametric EQ 2.

Dynamic EQ

• What it is: an EQ band whose gain changes according to the level in that band (or of an external signal). It is a cross between an EQ and a multiband compressor, but with the shape of a bell.
• Parameters: frequency, Q, threshold, range (how many dB it cuts or boosts at most), attack/release (often automatic, 1–20 ms / 50–200 ms), below- or above-threshold mode, internal or external sidechain.
• When: resonances that appear only on certain notes (vocal that “rings” at 2.5 kHz on high notes, bass that booms on one note), sibilance (alternative to the de-esser), kick masking the bass only when it plays (external sidechain from the kick onto the bass, 50–80 Hz band, range −3/−6 dB), vocal masking the guitar (vocal → guitar sidechain, 2–4 kHz, range −2/−4 dB).
• Plugins: FabFilter Pro-Q 3/4, TDR Nova (free), Waves F6, Ozone Dynamic EQ. In stock FL Studio the closest thing is Maximus or Fruity Multiband Compressor (multiband, not bell-shaped) or an EQ automated by Fruity Peak Controller.
• Mistakes: threshold too low (the band cuts all the time: it's a slower static EQ), release too short (distortion on low frequencies).

Linear phase EQ

• What it is: an FIR EQ that changes the amplitude without any relative phase rotation between frequencies.
• Price: latency (tens to hundreds of ms) and pre-ringing: with steep cuts or narrow boosts in the bass, an echo appears “before” the transient, which softens the attack of kick and snare.
• When: mastering, EQ on parallel buses or on several correlated tracks (where minimum phase would create differences between the signals), M/S EQ, multiband crossovers. On single tracks it is rarely needed.
• In FL Studio: Fruity Parametric EQ 2 in LIN mode (FFT, with adjustable precision: more precision = steeper slopes but more latency); Fruity Convolver with the “Linear phase EQ (Long/Short compensated)” presets; Frequency Splitter and Fruity Multiband Compressor (FIR) for linear crossovers. FL automatically compensates for the latency the plugin reports.
• Alternatives: Pro-Q (Linear Phase low/medium/high/very high/maximum, Natural Phase), Ozone EQ.

Mid/side EQ

• What it is: the stereo signal is encoded into Mid (M = (L+R)/2, what is the same in both channels: vocal, kick, bass, snare) and Side (S = (L−R)/2, the differences: wide guitars, reverbs, wide pads) and equalized separately.
• Typical uses: HP on the Side at 100–150 Hz (mono bass, more solid mix and vinyl-compatible); high shelf +1/+2 dB on the Side at 8–12 kHz (openness without touching the vocal); −1/−2 dB on the Mid at 250–400 Hz to remove mud from the center; −1 dB at 2–4 kHz on the Side if the wide guitars are harsh.
• Plugins: Pro-Q 3/4 (each band Stereo/Mid/Side/L/R), Ozone EQ, Brainworx bx_digital, TDR Nova (check the mode in your version). Fruity Parametric EQ 2 can monitor Mid, Side, L or R in the analyzer but cannot apply a band to the Mid only or the Side only: for stock M/S you need a setup in Patcher (M/S encoding with Fruity Stereo Shaper, EQ, decoding) or a dedicated plugin.
• Mistakes: strong boosts on the Side (over 3 dB) that make the mix incompatible with mono and fragile; cuts on the Mid that hollow out vocal and kick.

How to choose

Common mistakes

• Using linear phase on kick and snare with steep cuts in the bass: pre-ringing and a smeared transient.
• Pushed Pultec trick (Boost 8–10) on an already full bass: bloat below 60 Hz.
• Dynamic EQ instead of a compressor: if the whole track is dynamically unstable, compress first.
• M/S in the mix on single mono instruments (a mono track has no Side: nothing happens).

How to hear it

• Linear vs minimum: same 100 Hz HP cut at 48 dB/oct on a kick, listen to the attack: with linear a soft “pre-echo” appears.
• Pultec: with 60 Hz Boost 4 and Atten 3, listen to the change in the 150–300 Hz range compared with Boost alone.
• M/S: solo the Side (in Pro-Q or with the Fruity Parametric EQ 2 analyzer set to SIDE) and listen to what is really at the sides.