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.

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.

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 %

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

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

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

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