Live Sound EQ Basics: Equalization for Better Mixes

Live sound EQ basics provide essential knowledge for achieving clear, balanced mixes. Equalization allows shaping the frequency content of individual sources and the overall system response. Understanding how to identify and address frequency problems separates professional-sounding mixes from amateur efforts.

Understanding Frequency Ranges

Audio frequencies span from approximately 20 Hz to 20,000 Hz, representing the range of human hearing. Different instruments and voices produce energy at different points across this spectrum. Effective EQ work requires knowing which frequencies affect which sonic characteristics.

Sub-bass frequencies from 20 to 60 Hz provide physical impact felt more than heard. Kick drums, bass synthesizers, and the lowest bass guitar notes generate energy here. Too much sub-bass creates muddy, boomy sound while consuming amplifier power and speaker headroom.

Bass frequencies from 60 to 250 Hz contain the fundamental tones of kick drum, bass guitar, and floor tom. This range provides warmth and body to the overall mix. Excessive bass sounds bloated; insufficient bass sounds thin and weak.

Low midrange from 250 to 500 Hz holds much of the body of guitars, vocals, and snare drum. This range easily becomes muddy when multiple sources contribute energy. Careful management of low mids prevents mix clarity problems.

Midrange from 500 Hz to 2 kHz carries the primary musical content of most instruments and vocals. Intelligibility and presence live in this range. Too much energy here creates boxy, honky, or nasal qualities depending on the specific frequencies involved.

Upper midrange from 2 to 4 kHz provides presence and attack. Vocal intelligibility, guitar bite, and snare crack depend on this range. Excessive upper mids cause harshness and listening fatigue.

High frequencies from 4 to 10 kHz contain vocal sibilance, cymbal shimmer, and acoustic guitar sparkle. Too much brightness creates harsh, fatiguing sound. Too little sounds dull and muffled.

Air or brilliance from 10 to 20 kHz adds subtle openness and clarity. Many adults have reduced hearing sensitivity in this range. Boosting air frequencies requires care to avoid harshness from harmonics in the upper mids.

Types of EQ Controls

High-pass filters (also called low-cut filters) remove frequencies below a set cutoff point. Nearly every channel benefits from high-pass filtering to remove unwanted low-frequency content like stage rumble, handling noise, and microphone proximity effect. Common cutoff frequencies range from 80 to 120 Hz for most non-bass sources.

Low-pass filters remove frequencies above the cutoff point. These filters see less common use in live sound but can reduce hiss, radio frequency interference, or harsh high-frequency content from certain sources.

Shelving EQ affects all frequencies above (high shelf) or below (low shelf) the selected frequency. Turning up the high shelf brightens the overall sound, while boosting the low shelf adds warmth. Shelving EQ provides broad tonal adjustment.

Parametric EQ offers the most precise control with three adjustable parameters: frequency, gain, and Q (bandwidth). Selecting the center frequency, boosting or cutting at that frequency, and adjusting how wide the affected range spans allows surgical correction of specific problems.

Channel EQ Techniques

Start with high-pass filtering on every channel except kick drum and bass. This immediately reduces low-frequency buildup and clears up the mix foundation.

Listen for problems before reaching for EQ knobs. Identify what specifically sounds wrong—muddy, harsh, boomy, thin, nasal, boxy—then target the frequency range associated with that quality.

Use subtractive EQ as the first approach. Rather than boosting frequencies that sound weak, try cutting frequencies that mask the desired content. A vocal lacking presence may need 350 Hz cut rather than 3 kHz boost.

Narrow Q settings address specific problems without affecting adjacent frequencies. A resonant frequency in a snare drum benefits from narrow-band reduction. Wide Q settings make broader tonal changes appropriate for overall character adjustment.

Solo the channel to identify problems, but verify EQ decisions in the full mix context. A change that sounds good in solo may not translate when other instruments play simultaneously.

System EQ and Room Correction

Graphic equalizers on main outputs address room acoustics and system response anomalies. Room modes create frequency peaks and nulls that consistent EQ settings help manage. System EQ differs from channel EQ in purpose—it corrects the playback environment rather than shaping source content.

Pink noise testing reveals room response characteristics. Playing pink noise through the PA while measuring response with an analysis system shows where frequency anomalies occur. Visual representation helps identify problems the ear might miss.

Modest corrections work better than drastic changes. Cutting problem frequencies by 3-6 dB typically suffices. More aggressive cuts may indicate speaker placement or room treatment issues that EQ alone cannot solve.

Avoid boosting with system EQ. Adding gain at specific frequencies requires more amplifier power and speaker output capability. If certain frequencies seem lacking, cutting adjacent frequencies often achieves the perceived effect without increased power demands.

Common EQ Mistakes

Over-EQing individual channels creates phase issues and unnatural tones. Every EQ adjustment introduces some phase shift. Excessive processing accumulates these artifacts, degrading overall sound quality.

Boosting instead of cutting requires more gain throughout the system. A mix with many EQ boosts needs higher overall level, potentially causing amplifier clipping or speaker distress.

Neglecting context leads to poor decisions. A guitar sound EQ’d in isolation may conflict with keyboards occupying similar frequency space. All EQ choices should consider how sources fit together in the complete mix.

Copying EQ settings between sources ignores their unique characteristics. Every microphone, instrument, and performer differs. Settings that work for one vocal microphone may not suit another.

Forgetting to bypass and compare prevents evaluating whether EQ changes actually improve the sound. Temporarily disabling EQ reveals whether the changes help or simply add different coloration.