Equalizer

10-band parametric EQ — independent gain, frequency and Q per band.

Rockbox uses a parametric EQ rather than the more common graphic EQ. Each band has independent control of gain, centre frequency and bandwidth (Q), which buys you the same shaping power with fewer bands than a graphic EQ would need.

Using more bands than necessary wastes CPU and adds rounding noise. Disable or zero out bands you aren’t using.

Bands

Band	Filter type	Default centre / cutoff	Q recommendation
0	Low-shelf	32 Hz	0.7 (higher Q adds an unwanted boost near cutoff)
1–8	Peaking (bell)	64 / 125 / 250 / 500 / 1k / 2k / 4k / 8k Hz	Higher Q = narrower band
9	High-shelf	16 000 Hz	0.7

Per band:

• Cutoff / centre frequency — Hz
• Gain — dB; positive boosts, negative cuts
• Q — bandwidth (peak filters); 0.7 for shelves

Top-level settings

Setting	Storage	Type / range	Description
Enable EQ	eq_enabled	bool	Master on/off
Precut	eq_precut	0..24 dB	Negative gain applied before EQ to prevent clipping when boosting

Applied via dsp_set_eq_precut() and dsp_set_eq_coefs() in lib/rbcodec/dsp/eq.h.

TOML

eq_enabled = true
eq_precut  = 3      # 3 dB headroom before EQ

[[eq_band_settings]]   # band 0 (low shelf)
cutoff = 32
q      = 7         # Q × 10 — Rockbox stores fixed-point
gain   = 30        # dB × 10

[[eq_band_settings]]   # band 1
cutoff = 64
q      = 7
gain   = 0

# ... bands 2-9

q and gain are stored as fixed-point (×10) in global_settings. The GraphQL API accepts plain decimals — see Settings TOML reference.

Configuring via the API

GraphQL

mutation EnableEqAndShapeBass {
  saveSettings(input: {
    eqEnabled: true
    eqPrecut: -3
    eqBandSettings: [
      { cutoff: 60,    q: 7, gain:  3 }
      { cutoff: 200,   q: 7, gain:  0 }
      { cutoff: 800,   q: 7, gain:  0 }
      { cutoff: 4000,  q: 7, gain: -2 }
      { cutoff: 12000, q: 7, gain:  1 }
    ]
  }) { eqEnabled }
}