# Fader

> A mixer fader for Python — a console cap, FL Studio's style or a flat handle, vertical or as a crossfader, with an optional level meter beside the track.

Source: https://albakore.github.io/pyzed/audio/components/fader/

(Image: Three vertical faders with level meters and a horizontal crossfader moving)

**In plain words:**

A fader is the slider of a mixing desk: one per channel, usually for the volume. Drag the cap,
click anywhere on the track to jump there, or scroll over it.

```python
ui.audio.Fader(value=self.volume, caption="Master", level=engine.level()[1],
               on_change=lambda e: engine.set(out, "volume", e.value))
```

## How it works

- **Drag the cap** to move it; <kbd>Shift</kbd> makes the movement ten times finer.
- **Click on the track** (not on the cap) to jump to that point.
- **Scroll** to nudge it, **double-click** to reset it to `default`.
- `level` (0..1) draws a small meter beside the track: pass the channel's peak every frame and
  the fader doubles as a meter, like on a real console.

## Looks

| `variant` | Looks like |
| --- | --- |
| `"console"` | A grooved metal cap, like an analog mixing desk. |
| `"fl"` | FL Studio's dark cap with a colored line, the track filled up to it in `color`. |
| `"flat"` | A round handle on a filled track, matching the rest of the theme. |

`vertical=False` lays it out horizontally (a crossfader). `ticks` sets how many marks are drawn
along the track (`0` for none) and `length` its size in pixels.

## Properties

| Property | Default | What it does |
| --- | --- | --- |
| `value`, `min`, `max` | `0.75`, `0`, `1` | The value and its range. |
| `default`, `step`, `curve` | `None`, `None`, `"lin"` | As on the [knob](https://albakore.github.io/pyzed/audio/components/knob/). |
| `caption`, `unit`, `decimals` | | Text under it and how the value is written. |
| `length` | `160` | Length of the track in pixels. |
| `vertical` | `True` | `False` for a horizontal fader. |
| `variant` | `"console"` | `"console"`, `"fl"` or `"flat"`. |
| `ticks` | `11` | Marks along the track. |
| `level` | `None` | A 0..1 level drawn as a meter next to the track. |
| `color` | `"accent"` | The fill and the line on the cap. |
| `show_value`, `disabled` | `True`, `False` | |

Event: `on_change` with the new value.

**Tip:**

A mixer channel is a column: a [knob](https://albakore.github.io/pyzed/audio/components/knob/) for pan, two
[LED buttons](https://albakore.github.io/pyzed/audio/components/pads-and-buttons/) for mute and solo and a fader with its `level`.
The [MIDI controller demo](https://albakore.github.io/pyzed/audio/demos/midi-controller/) puts eight of them side by side.