DSP effects

Crossfeed, Haas surround, PBE, AFR, compressor and dithering.

The rbcodec DSP pipeline runs between the codec output and the active sink. All of these are bypassable; turn anything off by zeroing its enable flag.

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Crossfeed

Mixes a delayed and filtered portion of one channel into the other to simulate the spatial cues you’d get from loudspeakers. Particularly useful on headphones with hard-panned mixes (older rock/jazz).

Setting	Storage	Range	Default
Type	crossfeed	off / meier / custom	off
Direct gain	crossfeed_direct_gain	−60..0 dB (step 5)	−15 dB
Cross gain	crossfeed_cross_gain	−120..−30 dB	−60 dB
HF attenuation	crossfeed_hf_attenuation	−240..−60 dB	−160 dB
HF cutoff	crossfeed_hf_cutoff	500..2000 Hz	700 Hz

Crossfeed can cause output distortion if its settings result in a combined level that is too high.

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Haas surround

Adds an adjustable delay between channels to widen the stereo image. Four auxiliary controls move the perceived stage back toward the centre.

Setting	Storage	Range	Default
Enable	surround_enabled	0 / 5 / 8 / 10 / 15 / 30 ms	0 (off)
Balance	surround_balance	0..99 %	35 %
f(x1) HF cut	surround_fx1	600..8000 Hz (step 200)	3400 Hz
f(x2) LF cut	surround_fx2	40..400 Hz (step 40)	320 Hz
Side only	surround_method2	bool	false
Dry/wet mix	surround_mix	0..100 %	50 %

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Perceptual Bass Enhancement (PBE)

Group-delay correction plus a biophonic EQ to boost low-end perception.

Setting	Storage	Range	Default
Strength	pbe	0..100 % (step 25)	0 % (off)
Precut	pbe_precut	−4.5..0 dB (step 0.1)	−2.5 dB

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Auditory Fatigue Reduction (AFR)

Reduces energy in frequency bands the human ear is most sensitive to — helpful for long listening sessions.

Setting	Values	Default
AFR enable	off / weak / moderate / strong	off

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Compressor

Reduces dynamic range so quiet passages stay audible without loud passages clipping.

Setting	Storage	Values / range	Default
Threshold	.threshold	off / −3 / −6 / −9 / −12 / −15 / −18 / −21 / −24 dB	off
Makeup gain	.makeup_gain	off / auto	auto
Ratio	.ratio	2:1 / 4:1 / 6:1 / 10:1 / limit	2:1
Knee	.knee	hard / soft	soft
Attack time	.attack_time	0..30 ms (step 5)	5 ms
Release time	.release_time	100..1000 ms (step 100)	500 ms

[compressor_settings]
threshold    = -24
makeup_gain  = 0
ratio        = 4
knee         = 1
release_time = 300
attack_time  = 5

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Dithering

Most decoders work at higher than 16-bit precision; dithering adds a small shaped noise signal before truncation so the residual is uniform rather than signal-correlated. Most useful with classical music and other high-dynamic-range material.

dithering_enabled = true

• Algorithm: high-pass triangular distribution (HPTPDF)
• Noise shaper: third order, biased above ~10 kHz