> ## Documentation Index
> Fetch the complete documentation index at: https://rockboxzig.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# 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  |

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

## 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  |

```toml theme={"theme":{"light":"catppuccin-latte","dark":"min-dark"}}
[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.

```toml theme={"theme":{"light":"catppuccin-latte","dark":"min-dark"}}
dithering_enabled = true
```

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