Equalization by Frequency and Instrument: A Practical Mixing Guide.

Mastering equalization requires understanding how the audible spectrum ($20\text{ Hz}\text{ to }20\text{ kHz}$) is distributed between musical instruments and immediately recognising problem areas where undesirable resonances accumulate. This guide details key frequencies by instrument and precise solutions for the most common timbral mixing defects.

---

1. The Frequency Spectrum and Key Instruments

[ SPECTRAL MAP BY INSTRUMENT AND FREQUENCY RANGE ]

20 Hz      60 Hz      250 Hz      500 Hz      2 kHz      6 kHz      10 kHz     20 kHz
+----------+----------+-----------+-----------+----------+----------+----------+
|  SUB     |  BASS /  | MUD /     | BOXINESS /| PRESENCE / HARSHNESS| AIR /    |
| INFRA    | KICK     | BODY      | BOX       | CLARITY  | SIBILANCE| BRIGHT   |
+----------+----------+-----------+-----------+----------+----------+----------+
  [Kick Sub]            [Snare/Clap]            [Guitars / Synths]
             [Bass Synth]           [Piano/Strings]       [Vocals (Presence / Air)]
                                                          [Hi-Hats / Cymbals]

1.1 Kick and Sub-Bass

• Sub-Bass ($20\text{ Hz} - 60\text{ Hz}$): A physical pressure sensation. Requires pure sine-wave notes and rigorous envelope control. Ultra-steep high-pass filters at $20-25\text{ Hz}$ prevent subwoofer overload.
• Kick ($50\text{ Hz} - 100\text{ Hz}$ fundamental, $2.5\text{ kHz} - 5\text{ kHz}$ beater click): Cutting between $300\text{ Hz}$ and $500\text{ Hz}$ frees space for bass without losing punch or initial attack.

1.2 Bass

• Body and weight ($60\text{ Hz} - 150\text{ Hz}$): Defines presence on medium-sized systems.
• Note definition and harmonics ($700\text{ Hz} - 1.5\text{ kHz}$): Makes basslines audible on phone or laptop speakers without distorting the sub region.

1.3 Snare and Clap

• Body ($150\text{ Hz} - 250\text{ Hz}$): Provides solidity and fundamental impact.
• Attack and snare wires ($2\text{ kHz} - 5\text{ kHz}$): Adds projection and cut within a dense rhythmic context.

1.4 Hi-Hats and Secondary Percussion

• Body / Thickness ($300\text{ Hz} - 600\text{ Hz}$): Typically filtered with an HPF on electronic-music hi-hats to avoid interference.
• Brightness and definition ($7\text{ kHz} - 14\text{ kHz}$): Adds rhythmic openness and spatial width.

1.5 Pianos, Guitars and Synthesizers

• Piano and Strings ($100\text{ Hz} - 400\text{ Hz}$ body, $1\text{ kHz} - 3\text{ kHz}$ presence): Require low-mid attenuation to avoid clouding the mix’s centre.
• Synthesizers (Leads / Plucks / Pads): Presence lies between $1.5\text{ kHz}$ and $4\text{ kHz}$. Filtering at the extremes (HPF at $100\text{ Hz}$, gentle LPF at $16\text{ kHz}$) helps position them neatly.

1.6 Male and Female Vocals

• Male Vocals: Fundamental at $80\text{ Hz} - 200\text{ Hz}$. Warmth at $200\text{ Hz} - 400\text{ Hz}$, clarity at $2.5\text{ kHz} - 4\text{ kHz}$.
• Female Vocals: Fundamental at $160\text{ Hz} - 350\text{ Hz}$. Key presence at $3\text{ kHz} - 6\text{ kHz}$, articulation and air above $9\text{ kHz}$.

---

2. Diagnosing and Treating Frequency Defects

When mixing, associate the studio’s descriptive terms with their exact corrective-EQ frequencies:

2.1 Mud / Muddiness ($200\text{ Hz} - 500\text{ Hz}$)

• Cause: Excessive accumulation of lower harmonics from multiple instruments competing in the low-mid region.
• Solution: Gentle cuts with moderate Q ($-1.5\text{ to }-3\text{ dB}$) on secondary tracks (pianos, pads, guitars and reverbs).

2.2 Boxiness ($300\text{ Hz} - 600\text{ Hz}$)

• Cause: Resonances in small enclosures or hollow kick, snare and vocal timbres resembling speech inside a cardboard box.
• Solution: Apply a notch or narrow parametric EQ cut at $350-500\text{ Hz}$.

2.3 Nasality ($800\text{ Hz} - 1.5\text{ kHz}$)

• Cause: Excess energy concentrated strictly in the midrange, common in direct vocal recordings or closely placed dynamic microphones.
• Solution: Selective attenuation between $900\text{ Hz}$ and $1.2\text{ kHz}$.

2.4 Presence ($2\text{ kHz} - 5\text{ kHz}$)

• Function: The region of greatest human-ear sensitivity (Fletcher-Munson curve). Controls perceived intimacy and proximity of vocals and leads.
• Risk: An excess causes immediate listening fatigue.

2.5 Harshness ($3\text{ kHz} - 6\text{ kHz}$)

• Cause: Aggressive frequency accumulation in digitally saturated synthesizers, electric guitars or cymbals.
• Solution: Dynamic equalization or resonance suppressors (such as Soothe2 or broadband de-essers) to reduce harsh peaks only when they occur.

2.6 Hiss / Sibilance ($5\text{ kHz} - 9\text{ kHz}$)

• Cause: Peaks caused by vocal fricative consonants (“S”, “T”, “Z”) or overprocessed treble.
• Solution: A De-Esser focused on the exact hiss frequency, or notch cuts using multiband compression.

2.7 Air ($10\text{ kHz} - 20\text{ kHz}$)

• Function: A sense of three-dimensionality, openness and professional studio finish.
• Solution: Gentle boosting through a High-Pass / High Shelf filter above $12\text{ kHz}$ with minimum-phase or passive EQ.