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Chapter 13 / 21

EQ and filters

EQ changes the frequency balance rather than turning a fundamental note into another note.

EQ changes the frequency balance rather than turning a fundamental note into another note. A bell filter has Frequency, Gain, and Q. Positive Gain raises that region; negative Gain reduces it. High Q is narrower; low Q is wider. Width may work in the opposite direction to Q.

Graphic EQ has fixed band centers. Parametric EQ lets you choose frequency, gain, and Q; semi-parametric EQ exposes only some of them. A shelf changes the low or high region and then levels off. Low cut means high-pass; high cut means low-pass. A cut has a transition and slope, rather than a wall that removes every frequency beyond the cutoff. A notch makes a narrow, deep reduction; Tilt rotates the balance around a Pivot.

Prism offers Graphic 6, Studio Parametric, and Tilt. Tone Assist/Parametric EQ has ten bands and detailed controls. Its local guitar recommendations are not an AI model that reconstructs a pickup or reference sound. Suggestions do not automatically make music good. Static EQ differs from dynamic EQ, which changes a band's gain according to the signal.

Focus is a low-pass filter with resonance near its cutoff. Vowel/Wah sweeps a filter manually or follows the envelope in Auto Wah. Resonance can raise peaks even while the high end is cut. Wah changes frequency color rather than playing a new pitch.

To find a problem, use a moderate bell and move its center while playing the same phrase, then choose Q/Gain as needed. Narrow cuts are not the default for every band. Raising treble for brightness can also reveal hiss or fizz. EQ before drive affects distortion formation; EQ afterward shapes the resulting spectrum. A flat EQ curve does not require a flat guitar spectrum.

EQ response shapes · Concept illustration, not an engine measurement.

Concept references

Try the concept

EQ curve and spectrum

Why can an EQ boost raise Peak?

1,000 Hz
3.0 dB
1.00
Bell-filter response — gain dB versus frequency-12012201001k10k20kFrequency (Hz)
Bell-filter response — gain dB versus frequency
EQ response
Amplitude of five synthetic sines — not native band Peak-60-300201001k10k20kFrequency (Hz)
Amplitude of five synthetic sines — not native band Peak
InputOutput
Gain at the center frequency
3.00 dB
Input waveform Peak
-7.93 dBFS
Output waveform Peak
-6.92 dBFS

Boost increases sines near the center frequency. Their combined amplitude and phase change waveform Peak; an EQ gain value is not the overall Peak.

An RBJ peaking bell filter at 48 kHz, not native pedal voicing. The spectrum shows five synthetic sine waves; a sine or bin amplitude is not the filtered-band Peak in a Rigs meter.

Further reading

FabFilter — EQ band controlsFabFilter — EQ manual

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