# Crossover

> Splits audio into 2–4 Linkwitz-Riley bands, output as one band-major bundle whose bands sum back flat.

Source: https://docs.tune.toys/nodes/std.crossover/

A crossover splits a sound into frequency bands, so each can be processed on its own and added back together.

## What it does

Each split divides the signal into a low and a high band with Linkwitz-Riley filters, the kind used in loudspeaker crossovers: at the split frequency both bands are 6 dB down, and added together they give back the original level at every frequency. Lower bands also pass the allpass response of every split above them, so the phase of all bands lines up and the sum of every band is flat. Two bands split once, at Low split; three bands split at Low split and High split; four bands add Mid split between them. Split frequencies are used lowest first, so the bands always run from low to high.

The output is one bundle holding every band, band by band: with a stereo input and three bands it carries six channels, 1–2 the low band, 3–4 the middle and 5–6 the high band. Pick a band with [Select channels](https://docs.tune.toys/nodes/std.select/), process it, and add the bands back with a [Mixer](https://docs.tune.toys/nodes/std.mixer/). Because the number of bands sets how many channels the output carries, Bands is chosen on the node; a control or cable cannot drive it.

Slope sets how steeply each band falls past its split: LR12 is 12 dB per octave, LR24 24 dB and LR48 48 dB. Every slope sums flat. At LR12 each upper band is polarity-inverted, which is what makes that slope sum flat. The node adds no latency.

## When to use it

Use it to compress, distort, widen or delay one frequency range of a sound and leave the rest alone, or to send lows and highs to different places. For the common case of a three-band compressor in one node, use the [Multiband compressor](https://docs.tune.toys/nodes/std.multiband/); to shape tone without splitting, use the [Parametric EQ](https://docs.tune.toys/nodes/std.eq/).

## Ports

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| Port    | Direction | Signal | Lanes                   |
| ------- | --------- | ------ | ----------------------- |
| `audio` | Input     | Audio  | Inferred from the cable |
| `audio` | Output    | Audio  | Inferred from the cable |

<!-- ports:end -->

## Parameters

<!-- parameters:start -->

| Parameter | Label      | Range        | Default | Unit | Scale  | Notes                                                                                                                                    |
| --------- | ---------- | ------------ | ------- | ---- | ------ | ---------------------------------------------------------------------------------------------------------------------------------------- |
| `bands`   | Bands      | 2 to 4       | 3       |      | linear | Sets the output width to bands × input channels, so it is set on the node, never by a control or cable. Choices: 2 Two, 3 Three, 4 Four. |
| `low_hz`  | Low split  | 20 to 2000   | 200     | Hz   | log    | Top of the lowest band; the only split at two bands.                                                                                     |
| `mid_hz`  | Mid split  | 100 to 8000  | 1000    | Hz   | log    | Divides the middle into two bands at four bands. Shown when `bands` is 4.                                                                |
| `high_hz` | High split | 500 to 16000 | 4000    | Hz   | log    | Bottom of the highest band at three and four bands. Shown when `bands` is 3 or 4.                                                        |
| `slope`   | Slope      | 0 to 2       | 1       |      | linear | Linkwitz-Riley order: 12, 24 or 48 dB per octave. Every slope sums flat; LR12 inverts each upper band. Choices: 0 LR12, 1 LR24, 2 LR48.  |

<!-- parameters:end -->

### Bands (`bands`)

Two, three or four bands. The output carries this many copies of the input's channels, so it is set on the node, never by a control or cable.

### Low split (`low_hz`)

The top of the lowest band, from 20 to 2000 Hz. At two bands it is the only split.

### Mid split (`mid_hz`)

Divides the middle into two bands, from 100 to 8000 Hz. Used only at four bands.

### High split (`high_hz`)

The bottom of the highest band, from 500 to 16000 Hz, at three and four bands.

### Slope (`slope`)

The Linkwitz-Riley order: LR12, LR24 or LR48, for 12, 24 or 48 dB per octave.

## Tips

- Keep splits at least an octave apart so each band has room of its own.
- LR24 is the usual choice; LR48 isolates bands more sharply, LR12 overlaps them more gently.
- Leave a band's path empty to hear the other bands without it.

## See also

[Multiband compressor](https://docs.tune.toys/nodes/std.multiband/), [Select channels](https://docs.tune.toys/nodes/std.select/), [Parametric EQ](https://docs.tune.toys/nodes/std.eq/), [Filter](https://docs.tune.toys/nodes/std.svf/).